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PR

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April, 1937 NEWNES PRACTICAL MECHANICS 363

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Said a pal,"Welll never,Now isn't that clever.But 'who put you on to

Fluxite?"

See that FLUXITE is always by you-In the house-garage-workshop-wherever speedy soldering isneeded. Used for 30 years in government works and byleading engineers and manufacturers. Of Ironmongers-in tins, 4d., ad., 1 / 4 and 2/8. Ask to see the FLUX-ITE SMALL -SPACE SOLDERING SET-compact butsubstantial-complete with full instructions, 7/6.

Write for Free Boot on the ART OF " SOFT" SOLDERINGand ask for Leaflet on CASE -HARDENING STEEL andTEMPERING TOOLS with FLUXITE.

TO GYOLISTS I Your wheels will NOT keepround and tree unless the spokes are tied withflue wire at the crossings AND SOLDERED.This makes a much stronger wheel. WIsimple - with FLUXITE - but IMPORTANT.

THE FLUXITE GUNis always ready to putFluxite on the soldering lobinstantly. A little pressureplaces the right quantity onthe right spot and one charg-ing lasts for ages. Price 1/6.

ALL MECHANICS WILL HAVE\

FLUXITETT SIMPLIFIES ALL SOLDERINGFLUXITE Ltd.. Dept. P.M., Dragon Works, Bermondsey St.,

FOR BOYS YOUNG AND.OLD OUR

B 99 TELESCOPEis one of our well-known stand or hand -tele-scopes for look -out and astronomical use. A25x erecting day eyepiece and a 50x astroeyepiece with Sun -cap are provided, alsotripod stand with ball-and-socket joint.

Price £3 10 0Delivery free.

Send for lists of new and secondhand ;.Tele-scopes, Microscopes and Binoculars.

BROADHURSTCLARKSON & CO.

Telescope House, 63 Farringdon Rd., London, E.C.I.

BALDNESS BARS PROMOTION

A MODERN MIRACLEMEDICAL Science has at last discovered a simple

method whereby the dormant hair follicles can be re-stored to VIGOROUS LIFE, enabling them to producenew and naturally coloured hair.

One delighted Client of 89} who was bald -for over 3oyears reported that the "C.L.L." treatment produced aFINE GROWTH OF NEW HAIR. The ages of otherequally grateful Clients range from 22 to 81. MEDICALLYRECOMMENDED, £1,000 for denial.

Write to -day for a copy o our Illustrated Book entitled"HOW TO ACQUIRE PERFECT, HAIR GROWTH."Post free privately from:-

THE LABORATORIES (P.M.),37 New Bond Street, London, W.1.

The ONLY cure in the world for Baldness endorsedby the Press and the MEDICAL PROFESSION.

AMAZING CYCLE OFFER

/4t,a,., ri -.. ill

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ALL BRITISHJAGROSE ROADSTER. Built bya firm with 60 years' cycle experience.Est. 1876. Beats all agents and stores.Dunlop Rims, British Goodrich Tyres, PerryChain, Dunlop Saddle, British Hubs and Pedals,Ball -bearing Freewheel. Frame coslettised to preventrust, four coats Best Enamel, lined Red. Bright Parts Heavily Plated. FullyGuaranteed. Worth 0.15.0. Don't Delay. Take advantage now of thiswonderful offer.

FILL YOUR NAME IN NOW! FOR FREEIllustrated List of Roadsters, Racers and Tandems from 47/6

NAME

ADDRESS M.3.

JAMES GROSE LTD., 379 EUSTON RD., N.W.I



THIS IMPORTANT HANDBOOKON

SUCCESSFUL ENGINEERING CAREERS

FREE ON RE UESTAfter months of intensive effort and research, we arepleased to announce that the 1937 edition of our Hand-book, "ENGINEERING OPPORTUNITIES," is nowout of the publishers' hands and ready for free distribution.Containing 268 pages of practical guidance, this book is,beyond argument, the finest and most complete hand-book on Successful Engineering Careers ever compiled.It is a book that should be on the bookshelf of everyperson interested in engineering, whatever his age,position or experience.

The Handbook contains, among other intensely in-teresting matter, details of B.Sc., A.M.I.C.E.,A.M.I.Mech.E., A.M.I.E.E., A.M.I.A.E., A.M.I.W.T.,A.M.I.R.E., CIVIL SERVICE, and other importantEngineering Examinations : outlines courses in allbranches of CIVIL, MECHANICAL, ELECTRICAL,AUTOMOBILE, RADIO, TELEVISION and AERO-NAUTICAL ENGINEERING, BUILDING, GOVERN.MENT EMPLOYMENT, etc., and explains the uniqueadvantages of our Employment Department.

WE DEFINITELY GUARANTEE

"NO PASS NO FEE"If you are earning less than £.10 per week you cannot afford

to miss reading "ENGINEERINGOPPORTUNITIES." In your own in-

terests, we advise you to send for your copyof this enlightening guide to well -paid posts

by filling in and posting the coupon NOW.There is no cost or obligation of any kind.

BRITISH INSTITUTE OFENGINEERING TECHNOLOGY

410, SHAKESPEARE HOUSE,

17, 18, & 19, STRATFORD PLACE, LONDON, W.1

EP R

POSTTHIS

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BRITISH INSTITUTE OFENGINEERING TECHNOLOGY,

410, Shakespeare House,17-19, Stratford Place, W.I.

Please forward, Free of cost or obligation of anykind, your 268 page Handbook.

NAME

ADDRESS



PRACTICAL \rINMECHA\ ICS

EDITED BY F. J. CAMM

Testing Metal by Sound WavesA DEFECTOSCOPE for the testing of"metal up to 1 metre in thickness hasbeen invented by the Soviet scientist,Professor S. Y. Sokolov. With the aid ofthe instrument it will be possible to deter-mine the quality of metal with absoluteprecision before it has been put to use.The appliance is based on the ability ofsound to pass through metal.

Lloyd's Register ScholarshipsA SCHOLARSHIP, value £100 a year fOr"three years, and intended to assistmarine engineering students to take anadvanced course of instruction in engineer-ing subjects, is being offered by the generalcommittee of Lloyd's Register of Shipping.It will be awarded on results of the Student-ship Examination of the Institute in June.The age limit is 18 to 23 years.

Stamps Available

THEPostmaster -General announces that

King Edward VIII 21-cl. postage stampsare generally available at every Post Officein the kingdom, and will be supplied to anypurchaser who asks for them. If the stockat any office is temporarily exhausted, itwill be replenished without delay. KingGeorge V 214. stamps will continue to besupplied to purchasers who express nospecial preference.

Decimal CoinageMANY prominent leaders in industry

and public life throughout GreatBritain are co-operating in an effort tosecure the adoption of decimal coinage.

Electric Insulating MaterialsTHE building of a plant for the pro-

duction of electric insulating materialhas been commenced in the vicinity ofKhotkovo Station, near Moscow. Theplant is designed for an annual output ofgoods to the value of 100 million roubles.The first two shops will be put into opera-tion next year.

First Aerial BeaconTHE first aerial beacon to be erected in

New Zealand is being installed atHamilton. It will be of 3,000,000 candle-power, and will be visible in clear weatherat a distance of 25 miles.

Aviation in Southern RhodesiaTHE Prime Minister of Southern Rhodesia

I is setting up a committee to decide howbest to expend the gift of £3,500 by Sir AbeBailey for the assistance of civil aviationin the colony.

VOL IV. No. 43

APRIL

I 9 3 7

NOTES, NEWS,AND VIEWS

The Periscope HatAHAT fitted with mirrors, and known asthe periscope hat, has been designed for

use at race meetings, etc.

Glass Discs for Records(:". LASS dies are used in an ingenious

manner by a Weston -super -Mare manto make his own gramophone records.After much experimenting, he found apreparation with which to coat the surfaceof glass, and it is in this that the sound trackis made.

ENTER OUR GREAT NATIONALCONTEST FOR PETROL -DRIVEN

MODEL AIRCRAFT NOW !Turn to page 366

New French LinerTHE liner now being built to replace the

Atlantique, which was burnt in theChannel in 1933, is to be named Pasteur.

A New- Radio StationTHE Czechoslovak Telegraph Adminis-

tration has placed a contract withMarconi's Wireless Telegraph Co., Ltd.,for a high -power broadcasting station to beinstalled near Brno.

Synthetic SilkI N Hungary, chemists have succeeded inmaking synthetic silk from the bark of

mulberry trees.

Soviet Turbine of 100,000 kwt.I T is reported in a recent issue of a Sovietpaper that the Stalin metallurgical works

in Leningrad is making a powerful turbineof 100,000 kwt. with 3,000 revolutions perminute. Mr. M. 0. Grinberg, the directorof the plant, has stated that there is no

SUBSCRIPTION RATES

Inland and Abroad, 7s. 6d. per annumCanada - - is. per annumEditorial and Advertisement Offices " Practical

Mechanics," George Newnes Ltd.Tower House, Southampton Street, Strand, W.C.2.

'Phone: Temple Bar 4363.Telegrams : Newnes, Rand, London.

Registered at the G.P.O. for transmission byCanadian Magazine Post

turbine of equal capacity in Europe. Thenew turbine is expected to be ready inJuly next.A New Type of Seat

RAILWAY cars that are being builtunder the London Passenger Transport

Board's £40,0000,000 scheme, are to befitted with a new type of seat with a curveto suit the passenger's back.A Pedalless BicycleAT the recent B.I.F. in London was"shown a cycle known as the " GeeByke." It is a pedalless machine propelledby upward and downward motion of thesaddle.

The " Bicycle -Canoe "

AACOMBINED bicycle and canoe has

made its appearance in France. Thebicycle, which has very small wheels, drawsa trailer containing the canoe. The canoe,which is in three sections, can be taken topieces for carriage. The bicycle may alsobe taken to pieces to carry in the canoe.A Ship -to -Shore Telephone

ARADIO telephone has now been in-stalled to link up the Hull and Humber

ports with ships operating off the coast.A ship -to -shore telephone service is thusavailable at all times for trawlers, coastingcraft, and other vessels within a range of200 miles of the coast.Our £20 CarA READER, Mr. F. A. Halsey, has"completed the chassis of the £20 car,including engine, gearbox, back wheel, etc.He has taken the car out and it is quitesuccessful, although the body is not yetcompleted. Circumstances have arisenwhich will prevent him from doing so.He says that it would cost about £2 tocomplete it. He will accept £7 for it, thecar going to the first remittance received.Letters will be forwarded, and unsuccessfulapplications will be returned.Air Mail Between CitiesSIR Archdale Parkhill, Minister of Defence,

announced in Australia recently thatletter mails will, by the middle of next year,be carried by air between capital cities inAustralia at ordinary rates without anyform of surcharge. A surcharge would, itwas explained, be maintained temporarilyfor other services.Photographs

WILL readers please note that whensending photographs for publication

they should write their full name and addresson the back of each photograph, as well asa description of the model.



GREAT NATIONAL MODEL AIRCRAFT CONTEST!

1st PRIZE : £50Many other Valuable PRIZESNO ENTRANCE FEE !

START BUILDING THE "PETREL" NOW!Full Constructional Details of this Fine Petrol -drivenModel, and Rules of this Important Contest.

PRACTICAL MECHANICS takesgreat pleasure in announcing animportant National Model Air-

craft Contest, entrance to which isfree to every regular reader, and forwhich a first prize of £50 will beawarded, as well as the numerousother prizes to be announced later.

The Competition is for petrol -drivenmodels constructed from the planspublished here ; but in order that everyreader may be given a fair chance thedesign will be modified to suit mostof the small petrol engines rangingfrom 2 c.c. to 9 c.c. which are available.

Model Aircraft is making enormousstrides, particularly in America, Can-ada, Australia, and Germany, andwhilst interest in this country hasbeen rapidly developing during thepast two years, we are in some respectsstill far behind those countries. Thisis an unsatisfactory state of affairswhen we remember the pioneer workof early English experimenters suchas Stringfellow and others who madethe early work of the Wright Brotherspossible.

gr,wNGTHE/V/HOSTRINGERS OFg6'N'f%6"5PRacEArNOSE ONLY

CEZ:LL/L0/0WINDOWS

DETACHABLEELEHrRoni--"'-/VOSEP/ECEWITH 2.5o.c.,EN6/NE

The Advance of Miniature PetrolEngines

Our Competition, with its large andvaluable prize list, is specially plannedto give this fascinating scientifichobby the fillip which it deserves.There are hundreds of model air-craft clubs in this country, and thenumbers grow week by week. Thehobby is progressing from the rubber -driven model originally introduced bythe Frenchman Penaud as far backas 1871, to models propelled by minia-ture engines driven by compressed air,steam, and petrol. The two formertypes of engine have not been foundvery satisfactory, but there is a largenumber of entirely satisfactory mini-ature petrol engines on the marketwhich develop sufficient power to flymodels weighing up to 12 lbs., al-though the engines themselves weighonly from 6 oz. to 16 oz.Models which Fly for

over One Hour !It is a somewhat sur-

prising fact that the ori-

BALSA BLOCK To PREVENT /AILUNIT COMING FORWARD

CLOCK HEREBALSA PLATFORMSET AT CORRECTANGLE OF INCIDENCE

DETACHABLE UNDER-CARRIAGE MADE FROM/4 Sivo PIANO AV/RE &FA/RED WT../ SILXCOVERED Li.u.s.a. Perspective sketch of the fuselage and chassis of the "Petrel"

CO/L INSIDEHERE

DETACHABLE74iL WHEEL

iv/REHooirsTO RETAIN7A/L UNITBY ELASTICBANDS

kV/REA/00KB PROTRUDING FROMFUSELAGE (ATTACHED To SPEC/AL.5 PLY FORMERS) To TAKE ELASTICRETA/N/NG BANOS WINCH HOLDWING & ENG/NE AlocHyriNa ;

IN Po5/77oN .

3oz. 3 VOLT FLASH -LAMP BATTERY ISLIPPED BETWEEN FUSELAGE ANDBANDS WHICH .4/04.0 REAR SPRING LEGSOF UNDERCARRIAGE TOGETHER.

AMER/CAN LiaArrive/aArr WHEELS

ginal record for petrol -driven modelsof 51 secs. created by D. Stangermany years before the War held untilrecently, when Captain Bowden brokeit with a flight of 12 mins. 48 secs.out of sight. Actually the length offlight of a petrol -driven model is limitedonly by the amount of petrol carried,for these little engines will run for in-definite periods at speeds of about6,000 revolutions per minute. Theyare extremely reliable, and cheap.They thus make possible the con-struction of a realistic model, and onewhich simulates to a remarkable de-gree of fidelity the proportions, theappearance, and the performance of afull-size machine. It is one of the mostfascinating experiences to watch oneof these tiny models take off like a realaeroplane, and ascend to an enormousheight, with a crackle from the exhaustalmost as loud as that which issuesfrom the full-size machine.

COMPONENTS and MATERIALS REQUIREDENGINE MOUNT.-Elektron, as described.UNDERCARRIAGE. -8 ft. 14 S.W.G. wire and 2 reels of florist's

wire ; 2 pneumatic wheels ; 1 length *-in. sheet balsa for fairing ofundercarriage legs ; strip of silk for binding fairing.

FUSELAGE. -1 large tin of photopaste adhesive for silk coveting ;1 pint of clear glider dope (full-strength) ; 1 pint of coloured dope;four 3 -ft. lengths § in. x * in. birch or spruce for longerons ; three3 -ft. lengths * in. x * in. balsa for uprights and crosspieces ;12 in. x 4 in. of *-in. three-ply for special formers ; 4 in. x 4 in. x

in. three-ply for circular nosepiece ; small tube plastic wood forreinforcement ; 12 in. x 3 in. x 1 m.m. three-ply for fuselage floor(forward) ; four sheets of 3 ft. x 6 in. x lit in. balsa sheet for side,top and bottom covering of fuselage ; 12 in. of duralumin or brasstube to take 14 S.W.G. wire for undercarriage anchorage in fuselage ;6 -in. brass tube for tail wheel anchorage, to take 20 S.W.G. wire;1 light tail wheel ; 5 in. aluminium tubing, and cycle tubing to con-nect tank in wing ; 6 in. x 4 in. thin celluloid for cabin windows ;6 in. x 1* in. balsa block to make stops for mainplane and tailplane ;36 in. x 20 in. silk for covering fuselage ; 9 in. x 5 in. green baizeto make anti -slip platform coverings for wing and tail unit ;2 reels binding thread ; 3 ft. 18 S.W.G. wire for hooks.

MAINPLANE.-Four lengths of 3 ft. x in. x * in. spruce forrnainspars ; four lengths 3 ft. x 3 in. x * in. balsa sheet for ribsand riblets ; two pieces *-in. three-ply for central ribs ; 18 S.W.G.piano wire strengtheners at dihedral angle, fin, and undercarriagehooks; four lengths hard balsa 3 ft. x in. x in. for leading andtrailing edges ; 2 ft. round cane * in. diameter for wing tips ; twosolid balsa wing tip inserts, 3 in. x 6 in. x 1 in. ; four pieces ofjap silk 35 in. x 10 in. to cover wing.

TAILPLANE.-One sheet balsa 3 ft. x 6 in. x 4* in., and onesheet 3 ft. x * in. balsa for ribs and riblets ; one length spruce* in. x * in. for mainspars ; two lengths* in. x *in. balsa for leadingand trailing edges ; two pieces of silk 23 in. x 7 in. to cover tail-plane, and two pieces silk 7 in. x 8 in. to cover fin.

ODDMENTS.-Insulating tape ; ignition wire ; rubber bands ;two wireless terminal clips ; valve tubing for petrol connections ;two wireless plugs and sockets ; glasspaper ; cellulose aero glue(six large tubes).

ENGINE.-See text.



r2° oAcser

7,24eusr

I have dealt in my books (PowerDriven Model Aircraft, Is. or ls. 2cl.by post, and the Model Aircraft Book,3s. 6d. or 4s. by post) with most ofthe miniature petrol engines, and withthe principles of design, as well aspublishing in this journal my ownvery successful designs for petrol -driven models, as well as those sosuccessfully demonstrated by CaptainBowden. It is true to say that theefforts of this journal more than anyother have been responsible for thegreat interest now evinced in this newand simple scientific hobby.

A Fascinating HobbyThis is a scientific age and

more and more will aircraft playits part in the commercial andcivil life of the country. Theaircraft industry is full of op-portunities for those who knowthe principles of flight. Thereis no more certain way of acquir-ing this knowledge than bymeans of the building and flyingof model aeroplanes. In thisand other journals of which Iam the Editor I have regularlyfor more than twenty yearsdealt with model aircraft. Ihave scoured the world for

80

CLOCK

63""

3,4"234

I

3.

/0

2"1-*- -I 4"

OLIVEORAL ANGLE -/0 °

news, and published the latest designs.It is fitting, therefore, that this journalshould take the lead in promoting thisgreat National Contest which will notonly provide the great interest of in-door constructional work, but willcombine with it the great interest of

friendly rivalry which acontest alone invokes. It

/-W will also draw the atten-tion of the youth of this

6%2" country to a hobby inwhich even the non -tech-nical can partake andwith little cost.22"

-PETROL TANK-

CLOCKc.n

2

DOUBLE Li/yes DENOTE .3Pey FORMERSRE41.4/NDER - (.19 "x f/8 dAL.5.4 L/PRiair

CROSSP/ECES

Plan and side elevation of the" Petrel."

1. Only models built according to the designs andspecifications here given are eligible.

2. Notification of intention to compete must be senton a postcard, so that a register of competitors can becompiled. Address postcards to The Editor, PracticalMechanics, George Newnes, Ltd., Tower House,Southampton St., Strand, London, W.C.2, to reach usnot later than April 30th, 1937.

3. The Editor reserves the right to refuse an entrywithout assigning a reason.

4. Professional model -makers, those engaged in themaking of models for profit, or as a livelihood, areexcluded from this competition.

RULES(Competition Rules to be given next month)

5. Models must be the unaided work of the competitor,but they are allowed to purchase the usual finished parts-airscrew, ribs, wheels, engine, etc.

6. The competition is open only to regular readers,and competitors must, at a later date, send us thequery coupons, as evidence of purchase, cut from theApril, May and June issues of this journal.

7. The Editor of this journal, in conjunction withthe S.M.A.E., will frame the competition rules (to beannounced in the next issue) and will act as judges.Their decision is final and legally binding.

8. Each competitor may enter only one model.9. Any variation in the design may entail dis-

qualification, within the discretion of the judges.10. Those competitors who will be unable to attend

to fly the models themselves may appoint a delegate,approved by the judges, to do so.

11. The competition will be for time -controlledflight, marks being awarded for take -off, stability,duration of flight, and landing. The model with aquick take off may thus score points.

12. Other prizes will be awarded for workmanshipand finish.

13. The (Lev of the competition, which will takeplace at one of the large aerodromes, will be announcedlater.

Full -Size Blueprints Available See Page 368


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Rear view of the model.

The S.M.A.E. to AssistThe governing body of model

aeronautics in this country is theSociety of Model Aeronautical Engin-eers, who have kindly consented toact with us in framing the rules andjudging the competition.

The Contest will be held in July atone of the great Aerodromes of thiscountry, so that every reader hasample time to build his model and toperfect it. Arrangements will be madeso that those readers who cannotattend to fly the models themselvesmay appoint a delegate approved bythe S.M.A.E. to do so. Thus, everyreader will 'be given an equal op-portunity and distance will not confera disadvantage. The competition willnot be for duration. It is quite easyfor anyone to make a petrol -drivenmodel which will fly for an hour ormore. There are many instances ofmodels which have flown and landedover 60 miles away, having ascendedto an altitude of over 3,000 feet.Details of the Competition

Quite obviously a competition forduration would be difficult, if notalmost impossible to judge, for underthe rules of the S.M.A.E. the time-keepers are not allowed to follow themodel and the time is taken until themodel disappears from the sight ofthe timekeeper. If the competitionwere for duration there would be an en-ormous number of lost models, a largenumber of ties, and the competitorswould be penalised according to thelight at the time the flight was made.

So it is proposed to make the com-petition for time -controlled flight :the model will be required to take offand land within a specified time. Thisis possible by means of the simpletime -control switches, constructionaldetails of which are given. Markswill be awarded for a good take -offand a good landing, as well as for thestability of the model in flight ; butthe time of flight will also be takeninto consideration.

View of the engine mounting.

Other prizes will be awarded forworkmanship in a concours d'elegance.We shall award hundreds of consola-tion prizes. In order that we maymake the necessary arrangements itis important that every reader whowishes to enter the competition shouldwrite a postcard addressed to theEditor, "Practical Mechanics," GeorgeNewnes, Ltd., Tower House, South-ampton Street, Strand, W.C.2, statingthat fact.

The " Petrel "A suitable design for the competi-

tion is the " Petrel " illustrated here.This has been specially designed formodels up to 3 c.c., but we shallpublish details of the modifications

(very minor) necessary to convert themodel for 6 c.c. and 9 c.c. engines.The model must be constructed ac-cording to the specifications heregiven, so that all competitors areoperating under similar conditions.We cannot permit to be entered inthe competition models of the com-petitor's own design. This would beunfair to those competitors who havenot yet constructed a petrol -drivenmodel, for many model -makers alreadypossess petrol -driven models ; andunder no circumstances can we permitvariations of design, or specifications.

The model here shown has formedthe subject of articles in the twoprevious issues of PRACTICAL ME-CHANICS, but the drawings are repro -

This photograph shows the " Pet-rel" in flight. It is a fine flier.



The diagrams to the left show thetiming mechanism which presets thelength of flight. Below is shownthe electrical circuit for ignition.

duced here again for the benefit ofintending competitors ; they should,however, consult those two issues.

All of the materials are obtainablefrom advertisers in this journal, and

71N Daum To FirRouNo BUT NorTo TL,Licw)EScAPE-AfENT WHEEL JrFaVA LIOVERNOR

PART. .570,0LEVER

We can also supply a set of blue-prints, showing important parts full-size, for 58. Read the Rules carefully,and study the designs carefully beforecommencing construction.

Three-quarter front view of the model.

it is particularly important to orderthe engines first. Each supplier willthen have ample time to tune up theengines for competitors, and savethem a lot of work. Make up yourmind now to enter this great nationalcontest for petrol -driven models.

STREAML/NEO SOLO BALSA

TRA/L/N0 LOOPBALSA

MAIN SPARS..SPRUCE

ROUNDCANE

HOLLOWED OUTr'"'" UNDERNEATH FOR

LEAD/NO EDGE - Z/aHmessBALSA

STOP -START LEVER

............

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Daum WITH 60VERNOR INS/DE

3PLY PANEL

NAIL Acr5As POINTER

A MOVEABLECavrAcr

AXED CONTACT

ELECTRICALLEADS

%Tourers FOR 6RouNDBATTERY LEADS

angular form in order that it shall besimple to construct for the newcomerto model work. The top and bottomlongerons are of fin. by fin. square" medium " balsa wood. These lon-

The mainplane completed and ready for covering.

The FuselageThis is almost entirely made from

balsa wood, but, due to its construc-tion, is very strong. It is of rect-

Left : wing -tip con-struction and, right :centre section details.

gerons are laid along the longeronlines on the drawing and are kept inplace by means of small pins on eitherside. Two longerons are placed in

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D/INSION WITHOUT DOWELS ELASTIC BANDS BETWEENOR TONGUE HOOKS MARKED "X "HOLD

MVO NALIIES Of WINGLEFT frY/N6 HALF TOGETHER

NORMAL HooArsliozo BOTTOMOF SPLIT WINGTo PLATFORM

WING PLATFORM

position top and bottom, one abovethe other, so that both sides of thefuselage are made simultaneously.

Now Fin. by Fin. balsa uprights areglued in position everywhere exceptat No. 1, 3, 7, and 13 formers (see dia-gram). At these special positions three-

LAREEsr R/.6 FOR

2Y2"

"r.SLIGHT ONOERCAMBER

9"

HT WING I/ALF

Split -type wing centre section.

PIAAO WIRE HOOKSADDED AFTER CASTING.ELASTIC BANDS RETAINENG/NE MOUNTING ToFUSELAGE.ENO/NE LossBOLT ON HERE

FRONT VIEW.

sions can be drawn out from the sideelevation and the plan view of thefull-sized drawings. No. 1 former ismade from On. thick three-ply as it is

NA/NPLANE

-,4fe BALSA

BAMBOOFOR ELASTICBAND

No.8 RIB

4s'2"

-I 1-

74/4 Rid .

Rib forms for wing and tail.

ply wood formers are placed becausethese are the points where wire fittingsand strains occur. These three-ply for-mers, except No. 1, are all cut fromilff in. thick three-ply and well frettedout in the centre for lightness. They areof rectangular shape and their dimen-

MA/NSPARS

41';v leBALSA SPAR

RouNDCANE

the nosepieceextra strain.

Before fitting these three-ply for-

3

74"DEEP BOX TO FirINTO SQL/ARE ear INFRONT FUSELAGE

FORMER

REAR VIEW,

The detachable engine mounting.

mers, all the uprights must be gluedin and the glue set hard. To keep thebottom set of uprights from stickingto the top through any excess of glue,

2ND. LANsimarioN.46 "BALSA

6Loe

.3//c" BALSA OUTLINE

SILKCOVER/Na_

DOPED MTH ONECa4rOFCLEAN etioE/1.DOPE (FaLLSTRENGT/1)'1

WIRE NOOK FOR REAR ELASTICBA/V/MA I. BALSA SHEET ONLY

"x /8 BALSA SAAR

No %8"NOCK BALSA SHEET lifm/HAr/ON.

No 2. BALSA SHEET LAM/NATION

No 3. BALSA SNEETZAMINATioisi

LANI/NAT/oNS GLUED TosETHER a SrPEAML/NED.

The tail unit. This weighs complete Zit ozs.

L. E .

and has to withstand

4

7' C

e 92 3

7bP5PARL E .

IU

BOTTOMSPAR /

//2"DEER.y1 /"DEEp

2 3 4 6 7

little slips of greaseproof paper arepushed between the bottom and toplongerons where the uprights meetthe longerons after the bottom set ofuprights are glued into position.

(To be continued)

WING.

49 ° DIHEDRAL ANGLE

These diagrams show the method of laying out thewings, and (above) the wooden jig for building in the

dihedral angle.



air0/11/7101

What is a Unit of Value ?WHEN you compare the price of ,

an article with the amount ofmaterial and workmanship involvedin making it you form a conclusion asto whether the article is worth theprice asked. You say that the articleis cheap or dear, that it is worth theprice asked, or that it is not. If youwere asked to explain why youthought the article was good value orbad, you would find it difficult to sub-stantiate your opinion. When youbuy a pint of milk or a gallon of petrol,you have as a unit of value the im-perial pint measure, and the imperialgallon measure which are checked byGovernment officials. When com-paring one lathe with another or onewatch with another watch, one carwith another car, one make of wirelessset with another, you can only form anopinion as to relative value. There isno unit of value by which to measurevalues, and so it is customary to con-sider some previous purchase whichyou have made and mentally com-pare it with the purchase in prospect.The critical buyer takes everythinginto consideration-that indefinablesomething known as style, the qualityof the material, the quantity of thematerial, the amount of work neces-sary to make it, the probable demandfor the article, as well as making acomparison with the general appear-ance against the competitive products.

ComparisonSOME purchasers take as their unit

of value some item purchased at acheap store. Others take as theirunit a medium class article, whilst forthe cognoscenti only the best can beused for comparative purposes. Athing remains good or best only whilstthere is nothing as good or better withwhich to compare it. No one has yetdevised a formula for value. On oneside you may have a greedy manu-facturer who seeks to make an un-conscionable profit on an articlewhich is greatly in demand. Anothermanufacturer seeks to improve hissales by cutting his profits. Here a

direct comparison can be made, forobviously the latter will be givingbetter value per unit of money spent.

However badly, or well, an articleis made the demand for it will affectthe selling price, for the cost of thetools and the cost of marketing andadvertising must necessarily be cov-ered on the entire output and eachitem will bear a correspondingly largeor small chunk of it. Once the toolsare made that cost stands, irre-spective of the quantities run off, withperhaps a small allowance for the up-keep of the tools.

CamouflageNOWADAYS the art of camouflage

-of making a thing appeal to theeye only-has somewhat destroyedour sense of relative values. Takewatches ; you can purchase twowatches which look absolutely identi-cal, and yet they are of differentquality. The dials are probably madeby the same firm and so are the cases,but not the movements. The public,however, to -day picks a watch ac-cording to the appearance of its dial ;if the dial does not appeal the jewellerappeals in vain on the high quality ofthe movement. With cameras, it ismuch the same, and it certainly is withmotor cars which to -day are purchasedbecause of the preference of a parti-cular colour scheme, or a particularshape of body, on the part of the fairpassenger who will accompany thedriver.

It is so with periodicals. You can-not measure the value. If you are a

regular reader you spend 6s. per yearin buying PRACTICAL MECHANICS. Ifthe periodical is of use to you onlyonce in that period the subscription hasbeen worth it. Compare the valueof a technical journal and its costlyproduction, costly illustrations, costlyblocks, costly articles, costly distri-bution, and costly advertising, withthe cost of similar technical advice inother fields.

Technical AdviceYOU have a pain, and a doctor will

charge you anything from 5s. to7s. 6d. to tell you that it is a muscularpain. He does not cure it, however.No ! He invites you to take a pre-scription to the chemist and spendanother 28. 6d. in medicine. If youhave an aching tooth, a dentist willcharge you at least 5s. to extract it.If you consult a lawyer, it will cost youanything from £1 ls. upwards. In atechnical periodical you obtain for afew coppers a month the technicalservices of highly skilled people invarious technical and scientific fields ;experts whose education and trainingand experience have cost far morethan that of a doctor, or lawyer, ordentist. This point cannot be toostrongly stressed. Just think of thevariety of subjects which this journalalone deals with in the course of ayear. Reflect upon the remarkableFree Service we give in answeringreaders' queries on almost every sub-ject under the sun. Although wepublish only a tithe of them you willgauge the extent of this valuable

(Continued on vaae 422 )www.americanradiohistory.com


URGLARSI

AND HOW TO FOIL THEM

ADEQUATE protection against bur-glary usually necessitates quite a con-siderable expenditure on the part of

the householder, and even an insurancepolicy does not make allowances for thesentimental aspect of various losses, thus itis that the writer has effected a series ofinteresting designs and fitments which aresimple to follow, economical, and possess adegree of efficiency which should meet theaverage demands.

The house offers many points of easyaccess to the burglar. In considering Fig.1 it will be apparent that full precau-

tions would presumably require a system,whereby the entry by force or by easilyopened doors or windows, etc., would causethe alarm to operate over independent cir-cuits, and here then arises the question ofeconomy and security, since obviously theemployment of individual alarm circuits ateach vulnerable point of entry would meana large outlay in money to cover extensivewiring. The theoretical circuit Fig. 2shows one method of minimising the num-ber of wires in the circuit, and yet maintain-ing a consistency throughout. Now fromthis circuit it will be seen that a breach ofcontinuity at any point will cause a cessa-tion of current to the relay, which willrelease the armature, and the two back con-tacts will engage and complete an alarmcircuit. One suitable release system isshown theoretically in Fig. 3, and in utilis-ing this method, the relay shown in theanode circuit of the power valve must be sodesigned, as to give definite operation to thearmature which should remain held thewhole time the anode current is flowing.There are a number of anode circuit relays on

MAJOR CIRCUIT. (EXTERNAL)(b)

BACK GAR: DOOR FR: WINDOWS

GARAGE 1__ ROOM I

GARAGE 0 R --?"__To BUZZERIN BEDROOM

CI4VCONTACTS 'MAKE!'WHEN DOORS AREOPENED.

H

ITT

5 POLE SWITCH E40NA,&RELAY

/ FUSE. I FUSE.

RESISTANCE MAINS.LAME

LOUNGE

FR: WINDOWS

04

WINDOW

HALL

04

KITCHEN

ROOM 2

WINDOWS

CONTACT POINTS -04-.

Figs. 1 and 2.-A plan of a houseshowing the numerous places of entry bya burglar and (left) a theoretical circuitfor an alarm using a minimum number

of wires.

the market, and the employment of one inpreference to a home made relay, would bewell worth while, if the efficiency of the wholesystem is definitely to be assured. How-ever, a serviceable relay may be constructedwith the bobbins from old headphones, or

RADIATIONSUPPRESSORCONDENSER

EARTH

OLD POWERVALVE.

VOL: DROP RES,

SWITCH52

BIAS RES'.

- HOUSE CIRCUIT. -t -

S ERbtrilBY ONE aesiSWITCH.

SUPPLY Fig. 3.-A circuit for a(BA

mTius)T: or suitable release system.

cone speaker, but as the adjustment of thistype of relay is so critical, it is not to berecommended.

Another MethodAnother method which may be em-

ployed, is that using the D.C. mains in con -

CIRCUITFOR ALARM.

--- TOMAINS

--COPPER STRIPTOPREVENT ARMATUREBEING HELD BY

" RESIDUAL MAGNETISM

Fig. 4.-Details of a simple relay.

junction with an old " energised type "moving coil speaker, and Fig. 4 shows howthis may be accomplished. The wiringemployed, however, must be capable ofcarrying the mains voltage, and if extern-ally erected, should be lead covered orthreaded through conduit, the covering ineither case being earthed at more than onepoint.

Now owing to, the numerous types ofwindows and door designs, the measure-ments are left to the constructor ; however,the principal details are outlined in order



CONTACT WIRE SOLDEREDTO LEADED LIGHTS Having neatly wired the most important

fitments in the above manner, one mustnext pay attention to doors, and Figs. 7 and8 show " invisible " fitments which can berelied upon to give very satisfactory opera-tion. Here, again the metal used is brasssince this is soft and easily " worked."French Windows

Fig. 5. -Asystem where-by a windowcan be leftpartly openyet be wellprotectedagainst entryby a burglar.

that they may be of assistance, and a happy,medium is taken with regard to the designof the premises.

A Partly Open WindowIn certain cases a system is necessary

which permits a window to be left partlyopen, and Fig. 5 shows one method of main-taining continuity throughout the wholealarm circuit, at the same time guardingagainst entry by this window in like mannerto those which are closed.

Yet one or two difficulties arise whichmakes this secondary inclusion lacking inguaranteed efficiency ; for example, thewindow being open, the contact points areliable to be impaired by rust and deteriora-tion through being exposed to the weather.Again, unless a low -voltage circuit is to beemployed, the house personnel will beliable to shocks whilst handling the fittings,but its inclusion in this article is deemedquite useful since a step-down transformermay be used in conjunction with the mains,and a supply of the low order of 6 to 12volts employed, together with bell typebobbins acting as relay and cut : the (bat-tery) principle of which is shown in Fig. 4.Vaseline applied to the contact points isadvisable for protection against corrosion,etc.

Fig. 6 shows a simple window fitment con-structed of brass, and necessitating littleskill in assembly ; the more accurate thework is carried out, the more lasting andensured security ; by this is meant the neatconcealment of the wiring, etc., since a" snip " with wire cutters will render thewhole alarm system useless.

Another important feature of establishingan efficient system ,is that which arisesfrom the question of French windows, andFig. 9 shows a precautionary fitmentagainst the unbolting of these types ofdoors by breaking the glass and insertingthe hand.

Consider now another system which doesnot necessitate the wiring of all the win-dows and doors, but necessitates floor con-tacts. Here one has a neat system which is

Fig. 6.-A simplewindow fitment.

W &Z PIECES ARECONTACTED BYBALL CATCH"C°

OPENING OP DOORBREAKS CONTACTSAND OPERATES ALARMCIRCUIT.

and so the armature is attached, the twocontacts x and y are closed. Now the tipof this armature engages with a groove inthe armature of the unoperated electro-magnet Co and is held in place until thearmature of Co is attracted. This happenswhen Co is energised through the comple-tion of a circuit via the carpet operated con-tacts " P ." Leads are taken from thecontacts " x " and " y " and so anotherpoint is included in the alarm circuitthrough the house.

For a garage it would be a wise plan toadopt a method whereby two contactsoperate immediately the door is opened anda buzzer sounds in the house.

If by chance the property to be pro-tected is only accessible by a gate or door, asimilar circuit could be employed singularlyin this instance, and unless the trespasser

employed to quite a great extent, the onlydrawback being that the contact pointsmight be missed by the burglar when hehas made his entry. Thus it would seemthat very large surface plates, or a number offloor buttons would have to be fitted to copewith this eventually, and in these circum-stances it would preferable to compromisebetween the two systems, namely, " win-dow catch " and the " floor operated "type, and Fig. 10 shows a simple methodemploying a mechanically held relay.

The alarm is set first of all, by the opera-tion of the push button, and a circuit isimmediately completed for the relay " R,"

Fig. 10.-Asimple methodemploying amechanic allyheld relay.

LEADS FOR CIRCUIT PUSH BUTTON PORCONTINUITY. SETTING ALARM.

MAKEANDBREAK SPRICONTACTS

Figs. 7 and 8.-Two " invisible "

fitments for a door.

LEADS TO ALARMCIRCUIT.

TONGUE GUIDESHOWN CUTAWAY.

TONGUE OPLOCONCKTACTSOPERMES

scaled a wall or entered by any way otherthan by the gate, this system would proveitself of value.

BRASSCRP

,

FASHIONEDPREVENT BINDIBY BOLT HEAD

li

h,A. ,

Fig. 9.-A precautionaryfitment for French window.

ANTI -GAS AND AIR RAIDEQUIPMENT.

FILTERS for eliminating poison gas inhouses and shelters are shortly to bemanufactured in this country on a large

scale.Hitherto equipment of this type has been

very costly, but from a British firm whichhas been making extensive experiments,we understand that the price will be onlyan eighth of the cost of continental filtersand which are at present the chief source ofsupply. Production has already beencommenced in the factory of Andre (Com-ponents) Ltd., of Putney.

This new filter, which removes all tracesof poison gas from the atmosphere, involvesentirely new principles and at is operated

by an electric motor or by turning a smallhandle.

A further device, which has been de-veloped secretly, is to atomise a liquidantidote so that rooms already filled withpoison gas are rendered innocuous. Thephantomyste, as it is called, so finelyreduces the liquid antidote, that it stayssuspended in the air for several hours andhas proved effective in disinfecting gasmasks.

AERO ENGINEERING.

THE production of aeroplanes andaero engines requires a highly -specialised type of craftmanship.

The present rapid expansion of the industryhowever, is drawing into its ranks many

men who hitherto have been employed inother branches of engineering or associatedtrades. It is for such men that a newweekly part publication Aero Engineeringhas been produced. It is published byGeorge Newnes Ltd., and will be completedin about thirty-two parts: the price is 18. acopy. The first appeared on March 10th.

One of the primary objects of this workis to provide a comprehensive work ofreference on aircraft construction, pro-duction, maintenance and overhaul. Theinformation is contributed by men closelyassociated with production work in some ofthe largest aeroplane and engine factoriesin this country.

This work is very well illustrated bydrawings and photographs, whilst an inter-esting feature is the data sheets coveringthe most important types of 'plane.


April, 1937

A modern cinematograph projector for silentmade by Ross, Ltd.

NEWNES PRACTICAL MECHANICS

THE lot of the pioneer and inventor istraditionally a hard one. Many, in-deed, have been the inventors who, in

the pursuit of anticipated success, have beenreduced to hardship and sometimes to thedirest poverty. No inventor, however, hassuffered a harder fate than did Augustin LePrince, artist, engineer, mechanical genius,and one of the early pioneers of the cine-matograph and the moving -picture camera.Le Prince at the very height of his powerswas, by some mysterious agency, whippedsuddenly into an oblivion from which henever returned. The disappearance of LePrince has never been accounted for. Tothis day it remains, as it seems likely alwaysto remain, one of the strangest occurrencesin the annals of invention.

More than one inventor has been creditedwith the origination of the cinematograph,but there is no doubt of the fact thatAugustin Le Prince was the cinematograph'sreal creator, for he was the first to takemoving pictures from life with a single-lenscamera and to project them on to a screenby means of an arc light.

Born in FranceLouis Aim6 Augustin Le Prince, to give

the inventor his full name, was born atMetz, in France, on August 28th, 1842.His father was a French army officer, and itis rather significant to note that Le Prince*re was a personal friend of the great LouisJ. M. Daguerre, one of the originators ofphotography and the inventor of the verysuccessful daguerreotype process. It is onrecord that Daguerre gave young Le Princesome lessons in the photographic art andthat he aroused in the growing lad an en-thusiasm for photography and its applica-tions which, later on in his life, enabled himto devote his energies to the creation of thefirst successful cinema camera and projector.

375

MASTERS OFMECHANICS

N®o 2o.-An Inventor who Disappeared

The Strange Story of Augustin Le Prince, a Pioneerof the Cinematograph

Le Prince received a goodgeneral and technical edu-cation. He even went sofar as to do research workin chemistry at the Univer-sity of Leipzig. But besidesbeing a trained scientist,Le Prince happened to havebeen born an artist, andultimately, after a period ofindecision, he determined todevote his career to thepractical application of Art.

After a period of artistic training in Paris,Le Prince started as a painter of portraitsand also as a maker of art pottery.J. R. Whitley

It was during these early days that LePrince met the man who was destined toinfluence his entire career. This individualwas John R. Whitley, son of a brassfounderand engineer, of Leeds. Whitley had asister studying painting at Paris, and thislady, too, exerted a great influence upon thefuture career of Le Prince, for, ultimately,she became his wife and assisted him greatlyin his creative and inventive work.

The father of Le Prince's wife was JosephWhitley, founder of the firm of WhitleyPartners, brassfounders, of Leeds. ThisJoseph Whitley was quite an inventive in-dividual in his way, and, among otherthings, he devised the first commercial pro-cess of " spinning " molten metal for theproduction of what are termed " spun cast-ings." Le Prince, in 1866 visited Leedsand, owing to his friendship with John R.Whitley, was given a position on the staffof Whitley Partners, in which firm hebecame a designer. Le Prince married MissWhitley in 1869, and during the Franco-Prussian war of 1870 he served as anofficer in the French army, going throughthe siege of Paris unharmed.

On the cessation of hostilities Le Princereturned to Leeds, where, with his wife, hefounded a " School of Applied Art." Inaddition to running this school, Le Princespecialised in the production of art potteryand coloured photographs in enamel. Theventure was a successful one. Le Princeand his wife worked together in the closestharmony and they received commissionsfrom members of the Royal Family. Por-traits of Queen Victoria and of the

A series of motion photographs of a galloping horse obtained by Eadweard Muybridge. They constitute- someof the first motion photographs ever obtained.



renowned Mr. Gladstone executed by the LePrinces were placed, it is said, in the founda-tion stone of Cleopatra's Needle on theThames Embankment, along with othercontemporary records of the period.

" Living Pictures "Le Prince's attention was first turned to

the possibility of creating " living pictures "by the work of a certain Eadweard Muy-bridge, a native of Kingston -on -Thames,who was then engaged in photographic sur-vey work in California. Muybridge hadmanaged to take a series of instantaneousphotographs of a running horse and also ofother moving objects by means of a batteryof two dozen cameras, the shutters of whichwere released automatically by the consecu-tive movements of the animal. Subse-quently printing his series of photographs,Muybridge succeeded in reproducing theoriginal movements of the objects by meansof a simple viewing device.

There is no doubt that Eadweard Muy-bridge is entitled to be called the " firstfather " of the cinematograph, for it washe who first photographed movement andthen, in some manner, reproduced it. Muy-bridge, however, stuck in one groove allthrough his life, and as his particular groovehappened to be the wrong one he did notget very far with his work, despite the factthat he appears to have made a comfortableincome out of his moving images.

Le Prince became fascinated by the ideaof reproducing movement by means ofphotography. He made a few preliminaryexperiments on the subject in his Leedsstudio, but, at this juncture, he becameassociated with a new commercial decora-tive process which had been devised by hisbrother-in-law, and he went over to Americato assist in the introduction of the processin that country. Afterwards, on the sale ofthe American rights of the process, he actedas the manager of a concern in New Yorkwhich produced large stage panoramas andsimilar canvases. His wife, at this time,had obtained a post as a teacher of AppliedArt at an institute for the deaf in NewYork.

He Resumes his StudiesBeing friendly with the principal of this

institution, Le Prince was given permissionto use certain mechanical workshops be-longing to the institution, and he continuedhere the work on the photography of motionwhich he had begun at Leeds. As a result,he developed a crude form of motion -picturecamera and also a projector with a numberof lenses. It was in the workshops of thisDeaf Institution that Le Prince first pro-jected moving shadows upon a screen.Later, in 1886, Le Prince took out his firstAmerican patent covering the invention ofa moving -picture camera and a projector,or " deliverer," as he termed it.

Not long afterwards, Le Prince returnedto Leeds and, establishing a workshop inthat town, he gave himself up in earnest tothe construction of a moving -picturecamera and projector.

Le Prince's first cameras were of themulti -lens type. Within them, two bandsof sensitive paper or gelatine film werestretched side by side. The shutter -releasesof the lenses were actuated by electro-magnets, the latter being connected up to abattery and a rotary switch, which wasturned by a handle. As the latter wasmoved, the bands of film were exposed inconsecutive parts. The paper or film nega-tives thus produced were printed as glasspositives and these were fixed upon a band -like structure and passed through the pro-jector.

A Single-lens Camera and ProjectorHaving arrived at Leeds again, Le Prince

commenced the construction of a single-lens camera and projector. Within a yearhe had made two machines, in which thesensitive film was exposed at the rate of 12to 16 pictures per second. Reproductionsof two of the earliest of Le Prince's films ofthis period have survived. The first, takenin October 1888, shows some of Le Prince'srelatives in a garden at Leeds. The othershows a portion of the traffic of the periodpassing over Leeds bridge, being taken froma window overlooking the bridge.

Le Prince's great trouble at this time wasthe unsuitable nature of the sensitivematerial which he had to use, for celluloidas a film base came later. For the takingof the above -mentioned pictures Le Princeemployed sensitised paper bands. He alsoexperimented with gelatine films, glassstrips, and with other materials, but it wasonly after he had been able to procure sensi-tised celluloid sheets of reasonably trans-parent properties that the crowning successcame to his work. At first, the sensitive

An early cinematograph constructed by Le Prince.It employed a roll of sensitised paper.

celluloid used by Le Prince was only obtain-able in sheets of considerable size, which hadto be cut up into strips laboriously by handand subsequently joined together. Even-tually, however, sensitised celluloid in rolls-the progenitor of our modern roll films-came along and aided Le Prince enormouslyin this development of the cinema cameraand projector.

Le Prince's cinematograph projector gavehim far more trouble in its design and con-struction than did his early cameras. Theinventor found it necessary to modify thedesign of his projector continually, addingimprovement after improvement, gradually,thereby arriving at his desired result.

Commercialising his InventionAt last the inventor managed to con-

struct a projector which satisfied him forthe time being. The coming of celluloid asa base for sensitive film had removed themajor part of his photographic difficulties,and Le Prince now felt that the time was ripe

for the commercialisation of his invention.Accordingly, in the spring of 1890, 111

decided to return to New York and to takehis improved camera and projector withhim. He ordered special cases to be madefor the safe transport of his instruments,and arranged to sail for America in theautumn of the same year.

Before embarking for New York, LePrince took it into his head to make ahurried visit to France for the purpose ofattending to some patent affairs in thatcountry. Alas, however, a more ill-fateddecision could hardly ever have been made.Le Prince duly arrived in France and paida brief visit to his brother, an engineer andarchitect, of Dijon. Le Prince appears tohave been in high spirits at the time, and onSeptember 16th, 1890, he was seen off atthe railway station at Dijon by his brotherin a train bound for Paris.

His DisappearanceLe Prince, in stepping into that Paris -

bound train at Dijon, strode, virtually, outof human ken. He was never seen again.Whether he ever reached Paris or not is amatter for conjecture, as is also the modeof his lamentably tragic and altogether un-canny disappearance. Despite the factthat Le Prince had with him on the train aconsiderable amount of personal luggage andimportant papers connected with his inven-tions, these, too, disappeared as completelyas the man himself, and were never re-covered.

The case of Le Prince's disappearance wastaken up by the French authorities and anintensive search was carried out all over thecountry. Nothing ever came of it, how-ever, and, to this day, the extraordinarycircumstances of Le Prince's disappearanceremain a quite unsolved and, apparently,an ever insoluble mystery.

Mrs. Le Prince and others with her haveaverred that the inventor met a tragic fatein secret at the instigation of some indi-viduals interested in the commercialpossibilities of the cinematograph whowished to remove the master -inventor fromthe sphere of operations. By English law,Mrs. Le Prince had to wait for the elapseof the statutory seven years before herhusband could be " presumed dead " andbefore she could secure control of hispatents. By this time, however, otherworkers had entered the field of cine-matography. Hence, so far as any finan-cial results were concerned, the whole ofLe Prince's pioneer work in the creation ofthe cinematograph was lost to his family.

In July 1930, owing to the activities ofMr. E. Kilburn Scott, consulting engineer,of London, who, in 1889, had assisted LePrince with the electrical equipment of hiscinematograph projectors, a bronze tabletwas placed upon the front of the Leedsbuilding -150 Woodhouse Lane-wherethe ill-fated inventor had his workshop.The commemorative tablet was unveiled bythe Lord Mayor of Leeds in the presence ofthe wife of Le Prince, who had comespecially from New York for the occasion,and in that of a number of distinguishedengineers, scientists, and other interestedindividuals.

Recognition as a PioneerLouis Aime Augustin Le Prince thereby,

if somewhat belatedly, obtained recognitionas a pioneer of cinematography. Other in-ventors there were who improved upon andcommercialised his work. These, indeed,for the most part, reaped the benefits ofsuccess. Yet, without a doubt, much ofthe primary honour for the creation of thecinema is Le Prince's.



A W (el tchA Scientific Tool WhichEliminates Guessworkand Enables the RepairMan to accurately Setthe Rate of a Watch

THE Recorder consists of two units :the Recorder, which gives the writtenrecord of watch performance ; and the

frequency generator, which produces astandard frequency precise to one part in100,000, or a continuous accuracy of lessthan one second per day deviation.How the Recorder Works

The standard frequency output of thegenerator drives a synchronous motor whichrotates the drum of the Recorder at auniform rate of one revolution per beat of acorrect five -beat watch. The watch tobe tested is clamped in a spring mountingwhich can be rotated to give readings of thewatch in various positions. The mechanicalvibration in the case, due to the escapementimpact, is transmitted through a specialpick-up and amplifier, and the amplifiedtick of the watch operates a recording stylus.This stylus is mounted under the drum, andtravels the length of the drum actuated bya lead screw.

Chart paper is wrapped around thedrum, fed from a roll inside the drum,and the markings are made on thepaper by the stylus through a carbonribbon. If a watch is exactly correct,its tick will, repeat once every revolu-tion of the drum, and as the stylustraverses the width ofthe record, a line ofdots will be drawnwhich is parallel to themarkings on the chartpaper.

The top cover removed showingthe vacuum tube amplifier whichcontrols the recording stylus.

If the watch is fast, each tickwill come slightly in advance ofthe one before it, since the drum is rotatingat exactly the standard rate, and the resultwill be an upward -sloping line of dots. Ifthe watch is slow, the line slopes downward.The paper is so calibrated that the slope ofthe record can be read in seconds per day.

The operation of making a measurementis very simple.The watch isclamped in theholder, set in thedesired position,and the machineis started by asingle motion of

ecorderA front view of the Western Electric Watch Rate Recorder

showing the rotary drum which producesthe graphic record of watch performance.

the handle on thefront of the Re-corder. The ma-chine stops auto-

matically when the recordis completed.

Reading the RateThe time of the measure-

ment is determined by the speed ofthe lead screw. Two speeds areavailable through a selective gear

shift. Either a five -second or a thirty-second measurement may be made. Thefive -second record, for rough timing, gives areadable accuracy of fifteen seconds per day.The thirty-second record, being six timesas long, shows a greater cumulative errorin the watch, hence it is readable to twoseconds per day.

The machine makes an extremely flexibletool in the repair shop. Its major task isanalysis of watch perfoimance. Only shortexperience is required to become proficientin the simple procedure. Position error,isochronous error, and general average ratecan be determined by the machine. Inaddition, such faults as banking, low -motioneffect, loose pallet jewels, escape wheeleccentricity or tooth roughness, and otherescapement troubles, draw distinctive re-cords which immediately identify them.

When the fault is corrected, the machinepermits a quick verification of the repair, andcomplete regulation within a few minutes.

Although the machine is designed pri-marily for five -beat watches, it will alsomeasure the rate of any beat train, faster orslower than 18,000 beats per hour. Therating of a 21,600 or 19,800 -beat move-ment is as simple as an 18,000 movement.

Besides rating watches, the Recorder willtime alarm clocks, automobile clocks, timerecorders and meters, and other quicktrain movements which are too large tomount on the holder. This is done bysimply clipping a wire from the object tobe tested to the watch holder of the machine;the sensitivity is such that the vibrationtransmitted through the wire will operatethe machine. Hairsprings may also bevibrated by means of the Recorder. Anotherfeature is a headphone jack which enablesthe jeweller to hear the amplified tick of thewatch. This often proves a valuableaid in locating trouble.


Coal -cleaningRobotI N preparing large coal for the market thecoal has to be picked free from lumps of

shale and shaly coal. At present this isdone by hand picking from a travelling belt.A robot, electrically operated picker hasbeen devised to perform this tedious opera-tion. The coal is spread on to a table andjigged under wires which stroke the coal onthe top and sides. The wires carry a smallelectric current which passes through thelumps of coal or shale under the wires andthrough to the table. The electrical resist-ance of the shale is, however, less than that ofthe coal. The differences of electrical resist-ance can be magnified through valve relays.The currents thus set flowing by the wiresthen actuate gates in the path of the coal.If the wires feel that it is coal, the gate is leftopen and the coal jumps off the table on toa shoot. But if the current corresponds toa lump of shale, a bar rises in its path and itis tripped over so that it falls through a gapat the edge of the table. Very completeseparation of coal from dross is in this waysecured to a finer degree of selection than ispossible on the old hand-picking belt. Thisis one of the many examples of the finertechnique now being used for the prepara-tion of clean coal for the market.

THE LARGEST MOBILEDREDGE INTHE

WORLD.

The Illourghan Drag Line dredge, said to be the largest mobile dredge in the world.It is shown at work on the 11,000,000 dollar Ballona Channel Control Governmentproject, to carry off rain water from the motion picture city, Culver City, California.


THIS MONTH IN THESCIENCE AND

Detecting FishShoalsTHE automatic sounding machine which

has become a standard navigational aidaboard big ships finds a new use as a de-tector of fish shoals. The principle is tosend an electrically -timed sound wave downfrom the bottom of the ship. When itreaches the sea bed it is reflected back andits sound is caught again by apparatus onthe ship's hull which transmits it electricallyto a recording chart on the navigationbridge. The time interval between sendingout the sound and receiving back its echogives a measure of the distance of the seabed below the ship's bottom. In using thisapparatus to chart out fishing grounds aghost echo was sometimes recorded.Observation showed that this ghost eman-ated from the presence of shoals of herringsand other fish swimming below the surface.The vast numbers of fish in these shoalsacted as a dispersed reflector for the soundwave. It is now proposed to apply thisdiscovery to the detection of shoals forfleets of trawlers operating in conjunctionwith a leader equipped with sounding gear.

Five Mil-lion Volt

GeneratorA5,000,000 volt electro-static generator and

accumulator is being in-stalled by the Westing-house Electric Companyin America. The accumu-lator consists of a largehigh-pressure steel globe,50 ft. high and 30 ft. indiameter, mounted on theroof of the specially builtlaboratory and generatorhouse. Inside the vesselis a 15 -ft. diameter spheri-cal electrode mounted oninsulated columns. Theelectrode is insulated from

the globe and thedialectric mediumbetween the two ishigh-pressure air at120 lb. pressure.These high voltagesare generated by thefriction of rubberbelts over metal rodsusing exactly thesame principle, onlyon a magnified scale,as that used for gen-erating electrostaticcharges in the fami-liar Whimshurstmachine. The plantis meant for thestudy of the disin-tegration of the in-

nermost nuclear core of atoms. The highvoltages available will enable very highvelocity atomic particles to be shot intoatomic nuclei in the hope of producing newand more fundamental disintegrations thanthose which are already known.

Diamond ToothCutting Wheels

ASTEEL wheel studded with diamonds anddiamond dust is the latest contribution of

the inventor to the science of toolmaking.The wheel is primarily intended for use inmining gold -bearing quartz, which is so hardthat it is at present won by drilling and blast-ing. But other uses suggest themselves, suchas granite quarrying and glass cutting.Even tungsten carbide, which is the materialused for manufacture of the hardest ofknown steel cutting tools, can be shaped andmachined with a diamond wheel to thecleanest of cutting edges.

The wheels are made by pressingground -up diamond dust into a steel matrixalready turned up into the shape of a thin -edged wheel. Low-grade diamonds anddiamond dust which are useless as preciousstones are far cheaper and more readilyobtainable than is commonly known. Asthe diamond is the hardest of all knownsubstances, its efficacy as a cutter can read-ily be believed.

Boom in LightAlloysTHE national policy of air rearmament is

producing a boom in the manufacture ofthe light magnesium and aluminium alloysused in aeroplane manufacture and aero-en-gine construction. These alloys contain highpercentages of magnesium, which is the light-est metal known to science. The alloy ismade up with smaller amounts of alumin-ium, zinc, and manganese. Electron is oneof the best-known examples. Bulk forbulk, it is half the weight of aluminium, andonly a third the weight of steel, which itapproaches in strength. Factories are be-ing opened for extensive production atRainham, in Essex, at Manchester and atAvonmouth. The production of the Avon-mouth factory is said to be 150 tons a month.

" Grilled " HayTHE application of artificial drying of

grass is now being practised on anextensive experimental scale. The grass isdried in trays by gases from a coke firecooled down to about 150° Fahrenheit withair. A fan draws these hot gases over thegrass and dries a charge in a few hours.The plant is meant for operation over longperiods and is to be fed from fields on whichthe grass is cropped intensively through thesummer months, and cut at frequentintervals. The young dried grass obtainedin this way is said to form a better cattlefood than ordinary hay.



WORLD OFINVENTIONWorld's HighestFire Escape

AFIRE -ESCAPE ladder which hasrecently been constructed is capable of

reaching 180 ft. vertically into the air. Ithas been designed by the Leyland MotorCompany for the City of Hull Fire Brigade.The ladder is in six lengths, telescopinginto and folding on one another. Full ex-tension can be obtained within half a minuteby means of powerful winch gear. Canti-lever luffing gear and a rotary turntableenable it to be guided on to its mark bypointer controls from the operating tablebeneath. The lorry which acts as theanchor base has to be of very heavy con-struction. With the ladder it weighstwelve tons. Yet by means of specialbalancing gears this huge machine withheavy top load of ladder is enabled tocorner at full speed. The crow's nest at the

The 180 ft. Leyland fire escape, which is the highestin the world.

top, in which the fireman is fastened beforethe ladder is shot on its mark, has hose -directing gear and a small hoist for loweringrescued persons to the ground. Anescape of such dimensions is necessitated bythe rise in height line of modern buildings.

Use for a Death RayFLIES and insects at least can be de-stroyed by a real death ray. This de-

vice has already been explained in thescientific paragraphs of PRACTICAL ME-CHANICS. Two Danes discovered that ultra -short wireless waves at a short distancefrom the transmitter would actually killwasps, flies, and other insects. They passedultra -short waves between two rods, one on

either side of an open win-dow. Insects were temptedinto the death-trap by asaucer of honey. They in-variably dropped dead asthey passed through thewindow. An American,reading of this discovery,applied it to the bars ofspecial screens round theanimal cages of CaliforniaZoo. The animals insidethe cages were protectedthenceforward from allannoyance by flies. If onlythis sort of thing could bedone on a large scale themenace of air attack woulddisappear, that is untilscientists found an anti -death ray.

Dewavingthe Sea

RUSSIAN inventor haspatented a method of

smoothing out sea wavesfor the purpose of makingharbours usable for sea-planes in all weathers. The inventionconsists of a series of parallel pipes carryinga supply of compressed air thirty feet or sobelow the surface of the water. The steadyrelease of air from innumerable small holesin these pipes is said to damp out the swellof waves. Waves of four feet in heightfrom crest to hollow have been smoothedout on a small scale at a site in the Black Sea,and it is claimed that a more ambitious in-stallation would smooth out rollers of aconsiderably bigger size.

The invention may be of use in some of thesea-dromes which are being planned for theAtlantic and Pacific transits. These con-sist of large horsehoe-shaped steel pontoonsmoored to copper spheres sunk down intothe calmer depths of the ocean. These sea-dromes are to maintain their position by theforce of aerial screws.

A close upof the neonsignallingbeacon.

A Neon SignallingLamp

MR. R. C. WATKINS, of Merton Park,London, S.W., proprietor of the Super

Power Co., Clapham Common, has recentlyperfected an invention concerning a newkind of neon signalling lamp and beaconwhich is especially designed for aerodromesin isolated parts of the Empire. Alreadya dozen of these beacons have been sentto aerodromes in India and proved success-ful. The glass case with the neon tubingis fixed on to a metal box which containsthe main and battery-an easily charged12 -volt battery. The beacon has numerouscapabilities, including : It can be used forsending messages from an aerodrome to a'plane by using morse. A beacon can beplaced in each corner of the flying field and

used as boundary lights (red neon lightingcan be seen 5 or 6 miles away) ; it is fittedwith automatic morse which enables themachine to flash a message continuously.

World's DeepestMine

ANEW depth record has been estab-lished by the sinking of the new South

Deep shaft, of the Simmer and Jack's minesin the South African Rand, to 6,600 ft. Atthis depth a new and rich lode of quartzgold -bearing ore has been discovered. Pre-vailing high prices for gold make it profit-able to work at this great depth. So fardown in the earth the temperature rises toalmost 100° Fahrenheit, a temperaturewhich is too great for human beings to endurein comfort. To make the workings bearableto the miners, a refrigerating plant coolsthe ventilating air down to a more reason-able temperature. The depth attainedcompares with the depth records attained inoil borings which run down to the 10,000 -ft.mark or slightly over in some of theAmerican fields.

Gas MasksTHIRTY million gas masks are being

made ready by the Government forcivilian distribution in the event of nationalemergency. They consist of a simplerubber visor fitted with transparent cellu-lose acetate aperture for the eyes. Thebreathing filters are attached to the visorand contain wool packing to arrest noxiousdusts and smokes followed by an absorbentpacking of active carbon which gives com-plete protection from all gaseous poisons.


380 NEWNES PRACTICAL MECHANICS

Development of the St. Gotthard line, near Hassen.

April, 1937

By courtesy of the Swiss Federal Railways.

THE GREAT ALPINE TUNNELSTUNNELLING is an exceedingly ancientart, and the methods used continuedunchanged through the centuries until

quite modern times. There was a wonder-ful brick -lined subway under the EuphratesRiver, 12 ft. high and 15 ft. wide, which wasbuilt centuries before Christ, and Pliny-the old Roman historian-tells us of anotherwhich was made to drain Lake Fucino,which was an amazing work. It was 3+miles long, 10 ft. high, 6 ft. wide, andpassed under Monte Salviano. The worktook thirty thousand men eleven years toaccomplish.

It was not until the coming of the rail-ways that tunnelling began in real earnest.There are now more than four thousandrailway tunnels in the world, but thelongest subway is a conduit for water -supply. It is in Greene County, in theState of New York, and is more than 18miles in length.

The most remarkable tunnels in the worldare unquestionably the great Alpine bor-ings, all of which have been constructed in alittle more than half a century.

The Mont Cenis TunnelThe first of these was the Mont Cenis

Tunnel, begun in 1857. The rock was sohard, that hand power drilling was ex-ceedingly toilsome and tedious, the distancebored in twenty-four hours being less than

By G. Long, F. G S

There are now more thanfour thousand RailwayTunnels in the world, butthe most remarkable arethe Great Alpine Borings

eight feet. In 1861 machine drilling began,which increased the speed five -fold, andthe tunnel was opened for traffic in 1871.It is a fraction less than eight miles long,and cost £75 per linear foot.

As we study the history of Alpine tun-nelling, we shall see what tremendous im-provements were made by mechanising muchof the work, with the use of electricity,compressed air, etc., so that the cost oftunnelling has been reduced and the speedof the work increased. The Ancients boredtheir tunnels by hand labour, and movedstraight through from one side to the other.The rate of progress has been doubled bymodern engineers, by the simple idea ofboring the tunnel from both ends at thesame time, and meeting in the middle-andin nearly every case the two ends have metexactly-correct to a fraction of an inch.

There is something dramatic in this idea

of blasting forwards through the darkness,and the calculations to effect a successfulresult are intricate and difficult. There hasonly been one case in the history of railwaytunnels where the two ends have failed tomeet. This was due to no fault of theengineers, but to the criminal act of a dis-charged workman, who-for revenge-moved the pegs used for calculations duringthe night, and so falsified the result.

Courage and BraveryAs against this single act of baseness, we

can find many examples of courage andbravery, while few great engineering workshave ever been completed without the lossof many brave lives.

The boring of the St. Gotthard Tunnelwas the most difficult of the earlier worksof this kind. The task was undertaken byMons. L. Favre, who promised to completethe job in eight years for the sum of twomillions sterling. The terms of the con-tract were very harsh, for every DAY overthe ninth year Mons. Favre was to forfeit thesum of £200, and after six months the pen-alty was doubled.

No engineer had ever undertaken a taskof such magnitude. All workmen, tools,and materials had to be conveyed by asingle difficult mountain road to the twostarting places, Goschenen in the north, andAirolo on the south, the first about 3,640 ft.



above sea level, and the other 3,755, that ishigher than the top of the highest mountainin England. The way was impassible inwinter, and difficult at all seasons of theyear. The actual work was unhealthy andhard, the stifling confined atmosphere toldseverely on the workmen, who became paleand stooping, and tottered rather thanwalked, as they returned from their toil atthe end of the shift. More than threehundred of them were killed by accident,and nearly a thousand injured before thework was completed. Some were sweptaway by hidden torrents which suddenlyburst from the rock, many were killed byfalls of stone. Last of all the gallant Mons.Favre perished. He had been harassed bydifficulties of all kinds, financial and politi-cal as well as engineering, and though hestruggled gamely, the strain was too muchfor a system enfeebled by hardships, and hedied in a fit.

Magnificent SceneryThe tunnel to -day, and the railway to it,

form a favourite venue for tourists, owingto the magnificent scenery, as the iron roadclimbs through the pass, twisting and turn-ing like a serpent at the verge of terrificprecipices, and at one point doubling onitself through a spiral tunnel like a figure ofeight, so that the bewildered traveller whohas noticed a church on entering a darktunnel, sees it again in a different positionafter he has passed through. The St.Gotthard Tunnel is 9'3 miles long, and cost£48 a foot, it was begun in 1872 and com-pleted in 1881. The line was electrifiedthroughout in 1914-24.

The greatest of all mountain tunnels isthe mighty Simplon, which is 12.3 miles inlength, and took from 1898 to 1905 to build.The maximum depth below surface of thistremendous boring is '7,005 ft., and as aresult the heat was tremendous in theworkings, and formed a great barrier tosuccess, as the workmen were in danger ofbeing stifled. So a new and novel idea wasadopted. Instead of a single tunnel, twogalleries were pierced, 56 ft. apart, andconnected by lateral borings every 660 ft.,which enabled a satisfactory degree of ven-tilation to be obtained. When the workwas completed one of these galleries becamethe actual tunnel 191 ft. high and 161 ft.wide, the other was left as it was until theperiod of the Great War, when it was en -

Showing the remarkable spirals on the Gotthard.By courtesy of the Swiss

Federal Railways.

Kerstelenbach Viaduct, St. Gotthard. By courtesy of the SwissFederal Rathc,ys.

By courtesy of Me SwissThe Simplon line at Brigue, southern end of tunnel. Federal Railways.

larged and made into a second trackway,which was opened for traffic in 1922. Thetunnel is ventilated by electric fans, andthe trains are drawn through by electriclocomotives in 25 minutes.

The Simplon Tunnel.- Probably no other tunnel has been boredin face of such natural obstacles, but owingto the advance in mechanical and engineer-ing skill, all were overcome. The hero of theSimplon was Alfred Brandt, inventor, of therock -drill which bears his name. The toolis operated by water -pressure working atabout 15,000 lbs. per sq. in. It ploughs itsway through the hard rock by a rotarymovement, like a carpenter's augur throughwood. The wastage of drills is tremendous,however, so they are quickly scrapped andreplaced. The boring began at Iselle, andafter progressing about 21 miles, the" Great Spring " of cold water was en-countered. It burst from the rock in araging torrent with a pressure of 600 lbs.to the square inch, and an average volumeof more than ten thousand gallons perminute, which amount was almost doubledat times. Great rocks were hurled asidelike chips of wood, and the workmen fled



for their lives. Ultimately the water wascontrolled by conduits, but the next troublewas a hot spring. It burst from the rockscalding hot, at tremendous pressure, andwith a flow of 4,330 gallons per minute. Thetemperature was 113° F. This also held upwork for some time, but was ultimatelytamed. The brave Brandt did not live tosee the completion of the work, as he waskilled by a fall of rocks in the tunnel, whilesuperintending his workmen. The cost ofthe Simplon was £49 7s. per foot. The lineis now electrified, using locomotives of1,800 h.p. for passenger trains and 2,400 h.p.for goods trains.

A Recent TunnelThe Loetschberg Tunnel affords a strik-

ing example of the unknown and unpre-dictable risks which the engineer has to face.It is one of the most recent of all greatmountain borings, having been constructedbetween 1906 and 1911. The original planwas for a double track tunnel 8} miles inlength, but after they had penetrated thefirst two miles into the heart of the moun-

tain a frightful catastrophe occurred. Theshift were busy working on the rock facewith a battery of power drills when therewas a roar like thunder, and the whole" solid " cliff face caved in, as a mass ofmore than eight thousand cubic yards ofwater, sand, and boulders swept into thetunnel burying machines and workmen forever. Twenty-five brave men lost their lives,and none of the tools could be recovered.Anxious research by the engineers dis-closed the alarming fact that the mountainwas not solid as had been supposed, butthe very centre of it was cut through by thegorge of a prehistoric river, which hadfilled up with sand, boulders, and rocks,and so was invisible at the surface andcould not have been discovered by the sur-veyors. To drill through it was impossible,but its exact course was ascertained, andthe fault in the tunnel was blocked by hugebulkheads.

Then a new boring was made below thefault, and the line was bent to avoid it,thus adding more than half a mile to theexpected length.

A Striking Example

Perhaps the most striking example of thevalue of mechanised rock drills is that ofthe Arlberg Tunnel, six and a half miles inlength, which was bored in three years.This is only one mile less than the length ofthe Mont Cenis Tunnel, which took thirteenyears to complete. The Arlberg tunnel is26 ft. by 25 ft., and is situated in one of themost scenic sections of the Austrian Tyrolrailway.

Having myself travelled through all thesetunnels, I would mention that we are notonly impressed by the skill and daring ofthe engineers in boring the tunnels, but alsoby the amazing skill with which they havecarried the railway lines to these dizzyheights. The line clings to the side oflofty cliffs, crosses innumerable bridges ata great height, and twists and bends amonggigantic crags which almost make one dizzyto see.

No tourist who has the opportunityshould miss the chance of traversing one ofthese magnificent routes.

OUR 1111) USY INVENTORSThe following information is specially supplied to "Practical Mechanics," by Messrs. Hughes & Young(Est. 1829), Patent Agents, of 9 Warwick Court, High Holborn, London, W.C.1., who will be pleased to sendreaders, mentioning this paper, a copy of their handbook, "How to Patent an Invention," free of charge.

Ferric -FurnitureA CRITIC of the design of male dress"once complained that it consistedprincipally of tubes ; man wore tubes onhis arms, tubes on his legs, and a tube onhis head-the top hat. He might now addthat some of our furniture is composed ofmetal tubes. An inventor has recentlydevoted his energies to the improvement ofthis tubular furniture. Impressed withthe fact that an iron chair is not a lightweight, he has devised one in which the wallof the tube is not of uniform thickness.He places lengths of tube inside the frameto strengthen it at the points subject to thegreatest strain. Part of the frame is madeof tubing of greater diameter than the re-maining portion, and the ends of the latterare inserted into the former, providingdouble thickness. The inventor contendsthat an additional advantage of this con-trivance is that when, in the course of con-struction, the tubes are bent, the innertube does not shift.

This equipment for the home may betermed re-inforced ferric furniture.

Door and Raft

NUMEROUSdevices have been in-

vented for the benefit of those " inperil on the sea." Many of these appli-ances are on the lines of that improvised bythe Swiss Family Robinson. One of thelatest is a door which is convertible into araft. The special feature of this floatabledoor is that it has a flange and a groove,providing a gripping means for the ship-wrecked person, who, like the door, isunhinged.

A Hidden AdvertisementNVISIBLE writing which reveals itself

I when heated has been in existence formany years. The principle of this kind ofwriting has now been applied to the match.We are all familiar with the behaviour ofthe ordinary match. It begins life straight.Upon being burnt, it sometimes writhes likea martyr at the stake, after which it looksvery black, or should do so, as I under-stand that a neon -like incandescence which

does not die away quickly, is regarded, in amatch, as an imperfection.

An American has taken the tiny woodensplint which eventually becomes a match,and has prepared it in such a way as tominimise distortion, discoloration and re-duction to a fragile ash. On this slip ofwood there is printed a word or words, whichappear only after the match has been burnt.

This device should afford scope to theadvertiser. There is hardly room for aslogan, but the name of a proprietaryarticle might become visible. I can seemore than one possibility in connection withthis device. Apart from its use as a meansof publicity, it could be employed as anovelty or a game. A variety of hiddenwords might be included in a box of matches,giving an opportunity for guessing com-petitions.

A Spectacle Shield

THE spectacle case is at times somewhatelusive. When one wishes to put away

one's glasses, the case is occasionally missing.Consequently, the spectacles have to beplaced in the pobket without protection,which imperils the lenses.

In spectacles, as usually made, the side -pieces both fold down across the back of thelenses-the side nearer the eyes when theglasses are being worn. An improvedframe has now been invented, in which oneof the side -pieces is so connected to theframe that it can be folded down across thefront of the lenses. As a result, the glassesare shielded back and front, and thoughthis does not afford a guard equal to thecase, it reduces the possibility of damage.

Good News for Cinema PatronsI N cinemas, considerable inconvenience iscaused to patrons already seated by late-

comers, who, in order to reach the seatsallotted to them by the courteous usherettes,have to pass in front of the people in thesame row. As the space between the rowsis limited, it is usually necessary for theseated folk to stand to allow the late-comers to pass. This, in turn, obscures theview of persons in seats behind.

To obviate this inconvenience, there hasbeen devised a cinema chair which is soconstructed that it allows the sitter to pushthe seat portion of the chair backward,without rising. The movement is effectedby the person seated exerting pressure bymeans of the feet.

DYNAMO.

1 CATALOGUES RECEIVED

Multi -Models Ltd.IN a well -illustrated catalogue issued byMulti -Models Ltd., of 48 Beak Street,

Regent Street, London, W.1, several ex-amples of high-class model -making arelisted. These range from perfect replicasof various locos and coaches in all gaugesfrom the miniature 00 (or HO) to the large7i in. gauges. A particular feature of theproducts of this firm is the very high stan-dard of finish, due to the inclusion of aconsiderable amount of hand manufacture.To assist those who make their own rollingstock various spare parts are obtainable,including some very fine miniature nameand number plates for locos. These areperfect replicas and may be obtained in allgauges from 00 upwards. A very fine rangeof brick papers are also available, printedby a special colour process, and cost only2d. per sheet, 18 in. by 12 in. For signal,point, and line control a novel sectionalswitch assembly is obtainable and this hasalmost universal application. It is madein various sizes from 00 upwards, and maybe assembled to any desired combination.The catalogue costs 4d. by post.

A Free Leaflet of New Designs

EVERYONEwho makes things in wood

will be interested to have a new leafletoffered free by the makers of " Casco," thenew cold -water glue.

This leaflet is part of a new service-called the " Casco ' Project Plan-startedby the makers to meet the demand for newdesigns by homeworkers and schools. Themakers advertisement on page 362 in thisissue tells you where to send for the leaflet.

Lathe Work for AmateursHome Mechanics


9


THE MODERN MOTORENGINEER

This book places within the reach of themotor engineer and mechanic a completecourse of technical instruction on everydetail of work in the maintenance, repair,overhaul and tuning of every kind of motor -propelled vehicle. The new and revisededition will be a real boon to the motorengineer, as it deals with all the most recentdevelopments, such as the Diesel Com-mercial Engine, the Pre -selective and Syn-chromesh Gear Boxes, the Fluid Flywheel,Fuel Pumps, Hydraulic and Vacuum Brakes,etc.

HANDLING BREAKDOWNS ONTHE ROAD

A feature of special value is the sectiondealing with breakdowns on the road ; herewill be found first-class instruction andadvice as to how repairs in these circum-stances can be most quickly and effectivelycarried out. General repairs are treated inthe widest sense, and instruction is given insoldering, welding, brazing, sheet metalwork, machining and grinding. Repairs toradiators, bonnets, lamps and body -workare also dealt with.

THE SCOPE OF THE WORKAmong the other subjects dealt with are :

The Dismantling, Tuning and Repair ofEngines, Clutches, Carburettors, Gear Boxes,Axles, Brakes, Accumulators, Batteries,Magnetos, etc.-Armature Winding-Gar-age Tools and Mechanical Equipment-Petrol and Oil Pumps-How to cost GarageJobs-The Law's Requirements, etc., etc.Fault-finding Charts and electrical circuitdiagrams are also included.

THE ILLUSTRATIONS" The Modern Motor Engineer " is

excellently illustrated, all the illustrationshaving been chosen for their practical valueto the reader in following the text. Thereare 24 full -page plates and over ',too photo-graphs and diagrams in the text.

THE MOTOR ENGINEER'SCHART

Supplied free with the new edition of" The Modern Motor Engineer " is aspecially prepared Chart which shows bymeans of diagrams and tables all the inform-ation regarding measurements, etc., whichthe engineer or mechanic is likely to requirein his day-to-day work.

A FREE BOOKLETTo the Caxton Publishing Co., Ltd.,

119, Clun House, Surrey Street,London, W.C.2.

Please send me, free of charge, Book-let, describing " The Modern MotorEngineer."

NameSend this form in unsealed envelope

(id. stamp).

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MODERN ELECTRIC

WIRINGThe New and Revised Edition of " Modern

Electric Wiring " is a practical guide to thewiring of Private Dwellings, BusinessPremises, Factories, and Public Buildings,for Lighting, Heating and Power, withchapters on Wireless Practice, ElectricMotors; Talking Picture Equipment, andNeon Illumination.

The author has had a wide and variedexperience in the practice of wiring, and istherefore able to describe in detail how everyphase of the work should be carried out.

THE SCOPE OF THE WORKGeneral Principles of Electrical Con-

ductivity - Materials -Wire Gauges - In-sulators, Insulation, and Resistances-Systems of Wiring-Safety Fuses-Illumin-ation, Heaters, Cookers, Small Motors,Appliances -Wiring Layouts - Lighting,Heating, and Cooking-Temporary Wiring-Measuring Instruments, Meters, andMains-Bells and Signals-Domestic Tele-phones-Testing-Wiring for Wireless In-stallations-Power Amplifiers, Public Speechand Talking Picture Equipment-The Work-shop-Electric Motors and Generators-Principle of Neon Illumination-Specifica-tions, etc.

THE WORKSHOPTo the ambitious wireman, anxious

to commence business, the chapter on theworkshop will be full of interest because,apart from equipment and routine (withspecimens of time and material sheets), thebusiness side is also discussed and usefulhints given as to carrying out work, stock-taking, calculating profits, etc.

THE ILLUSTRATIONS" Modern Electric Wiring " contains over

27o illustrations, the majority of which arewiring diagrams, special designed todemonstrate practical working, and many ofthem suitable for use in actual practice.

AN OPINIONMr. G. B. BENNETT, Tudor Road,

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Wiring.' It treats a big subject in a mannerremarkably easy to understand. It is thebest book on Electric Wiring I have seen."


19, Clun House, Surrey Street,London, W.C.2.

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ENGINEERING

WORKSHOP PRACTICEThis entirely new book provides a com

plete practical course of instruction in everyimportant branch of engineering workshopmethods, materials, and equipment. Itdeals with the underlying principles, crafts-manship, machines, tools, measuring processes and machining methods of to -day, andit will prove indispensable to the engineer,draughtsman, mechanic, apprentice, andengineering student. Its scope extends fromsimple hand tools to the latest elaboratemachines employed for mass -productionpurposes.

DATA AND RECIPESApart from the mass of practical instruc-

tional and descriptive information given,there is a wealth of data, formula, workshoprecipes, hints and tips which render thisbook a valuable reference work for allconnected with engineering.

SOME OF THE SUBJECTSHand Tools, Measuring Methods, Ver-

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April, 1937 NEWNES PRACTICAL MECHANICS

Overhauling a

Renewing the gilding on the front of the piano.

THE chief troubles affecting mostpianos are dampness, disuse, and mis-use; the former, however, is more pre-

dominant. In a great measure this is dueto the construction of the modern piano, inwhich metal enters into the constructionmuch more than formerly. People insiston an iron frame, but in the majority ofcases, they do not realise that this is apt toencourage dampness. The iron frame ofthe piano being extremely cold, admissionof a warm air will cause condensation onthe metal and rust results. A piano doesnot improve by being left unused for aconsiderable time. It should be in constantuse and then, contrary to popular opinion,tuning is less frequently required. On theother hand misuse, caused by children beingallowed to bang on the keys is, of course,to be avoided. A piano is generally mostused during holiday seasons, when, possibly,it may receive rougher treatment thanat any other time of the year. Conse-quently, the following weeks are a goodtime to give it an overhaul and thoroughcleaning.

Removing DustThe first thing to do after opening the

front is to remove all dust which may haveaccumulated inside. It may be discoveredthen that some rust has made its appear-ance on parts of the ironwork and steel,even when nickel or chromium plated.The best way to treat this is not to removeit altogether, as this may do more harmthan good, especially in the case of thewires. The most satisfactory treatment isto take a piece of coarse cloth, such as feltor tweed from an old coat, dip it in somelinseed oil and rub as much of the rustaway as possible, at the same time investingthe iron with a protective film of the oil toprevent further rusting.

On no account should oil or grease beallowed to get upon the wooden mechanismof the piano as it may interfere with theaction by causing swelling of the wood. Toassist the smooth working of wooden partsthere is nothing better than dusting a littleof the finest mica powder between thejoints, or any bearings. Black lead wasused formerly for this purpose but micapowder, or fine French chalk, is better.Only the bare minimum required should beused-too much only tends to clog andimpede action.

Hardened FeltsSometimes the tone of a piano has de-

teriorated through the hardening of the

Although theHandyman Can.not Hope toOverhaul a Pianoas Efficiently as aPiano Repairer,he can at Least

enefit by theUseful Hints

given belowfelt on the hammers, more particularly onthose in the centre where the most constantwear occurs. An improvement can beeffected in this direction by taking a strongneedle and pricking the felt pads as thislightens them and lets in the air. This is amatter of patience and the piano repaireruses a special tool for this job, but as it is

If the tone of the piano deteriorates through thehardening of the felts of the hammers an improve-ment can be affected by pricking the felts with

a needle.

not usually available for the amateur, hemay not accomplish the task so speedily,yet with perseverance he may be successfulin greatly improving the tone.

If, on opening the interior of the piano a

Cleaning the notes of the piano.

385

Piano

Renovating sconces with lacquer.

wire is found to be broken, or other seriousdamage has arisen it is not advised herethat the reader should attempt to rectify itunless possessed of the expert knowledgerequisite for a successful result. Piano re-pairing is highly specialised work but allthe hints and advice given here can becarried out by a man of average intelligence,leaving that which may involve more harmthan good for the trained workman tocarry out.

Cleaning the KeysA job that the ordinary reader can ac-

complish successfully is the cleaning of thekeys and the case. Unless the keys arevery badly stained and worn it will not benecessary to remove them to effect animprovement. Raise the key from thefront, and, holding it firmly with the lefthand, use the other hand to briskly rub overthe key with a piece of felt dipped inmethylated spirit. Each key is taken inturn and served in the same manner whenthe colour will be greatly improved. If astrong scent of camphor is noticed whenthe methylated spirit is applied, it indicatesthat the keys are not covered with ivorybut with celluloid.

Renewing GildingIn cleaning the outside it may be re-

quired to renew the gilding, or some of it.If the surface of this has worn uneven itwill be necessary to smooth down levelwith fine glasspaper. After dusting offapply with a camel hair brush a coating ofgold size, or white of egg beaten into aliquid state. When this gets tacky applythe gold leaf, pressing in with a velvet pad.When quite dry, the superfluous gold canbe removed with a brush. Only the bestgold leaf is used on pianos and this isadvised here for regilding, especially whereonly a little is required.

The cleaning of the case is quite simpleand usually satisfactory if the propermethods are employed. Some people con-sider that the application of equal parts ofturpentine and sweet oil gives best results,but the writer prefers to use only boiledlinseed oil which assists the polish and workseasier. Partially soaked in the oil, but notmade so oily that there is any drip from it,a piece of felt is briskly rubbed over thesurface and a surprisingly rapid improve-ment takes place. Dirt is quickly removedand the grain of the wood shows up asnew.

The only snag that may be found in thisprocess is in cleaning off the oil. To be a


la


success it is imperative that this be thor-oughly done. One, or two soft dustersmust be briskly applied, preferably warm,until the case is free from smears. It iswise not to be sparing in the number ofclean dusters, as the finishing off can scarce-ly be overdone.

SconcesIf there are sconces it will be necessary to

renovate them. To do this the old lacqueron them must be removed, and the bestway of doing this is to soak them in petrolfor roughly an hour, away from artificiallight and bright sunshine. The lacquerwill then brush off, and, after drying, thesconces can be polished with a soft leather.

If carefully done they will be found toregain their lustre and can then be lac-quered.

When polishing, no grease must be usedand even finger marks must be avoided, orthe lacquer, when dry, will peel off. Toavoid this, handle them carefully. Beforeapplying the lacquer, the sconces must beheated. The correct heat should be toohot to hold with the fingers but not enoughto make the lacquer sizzle on the metal.Lacquer being sometimes difficult to obtainin some parts of the country, it is worthremembering that clear white spirit varnishmay answer the purpose, but the metalmust be only warmed for this, and then ittakes some time to dry.

Jingling NoisesDo not decorate the top of the piano with

vases of flowers with water in them. Onlycall in the tuner when imperatively neces-sary ; many pianos are spoilt by too fre-quent tuning. Jingling noises heard in apiano when played may be due to infre-quent use. When not due to this they will,generally, be found to be caused by someloose article on the top of the instrument ornear enough to it to set up a vibration whenstriking one or two particular notes.

During the summer when the piano israrely used, damage may be done to thefelts by moths. This can be prevented bydropping a carbon ball down clear of themechanism at each end inside the piano.

L©W TEMFFIRATLEF-SUMIEFILE -MU CUNSIIIDEIRATEDXS

y F. W. Britton, D.Sc.

Absolute Zero-So Near Yet So Far.SCIENTISTS have now reached to with-in three thousandths of a degree ofabsolute zero, with the aid of liquid

helium and magnetic fields. It would besuperfluous to refer again to the wonderfulthings that can be done through the mediumof liquid air, for this has already been fullydealt with by the recent well -illustratedarticle appearing in this journal (February).But I want to speak about the peculiarfeatures of these excessively low tempera-tures, because the attention of the publichas been drawn to them in the Exhibitionheld last March at South Kensington.

Difficulties in Low Temperature ResearchAbsolute zero means, of course, that

there is at this point a complete absence ofheat altogether ; and really, this degreedoes not seem particularly low-only- 273° C. below the freezing point ofwater. It is easy to reach a thousand ortwo degrees ABOVE the freezing point, sowhy shouldn't we be able to get BELOW ita paltry few hundred degrees ? Now justremember how long it took physicists toattain such low temperatures-the problemhas been wrestled with for over a hundredyears at least. One of the most difficultfactors which confronted experimenterswas that of suitable means for obtaininghigh pressures. This came with the adventof modern mechanical inventions, thusmaking it possible to compress air to thepoint of liquefaction, then, using this toliquefy hydrogen, which, in turn, can liquefyhelium, so that, since this represents thelimit of physical liquefaction, we arrive at adegree above the Absolute zero. Ulti-mately, it is possible to reach to withinthree -thousandths of a degree of absolutecold as we shall see.

Enormous Pressure NecessaryA good conception of the enormous

pressures needed for gas liquefaction isgiven from that of common carbon dioxidewhich requires 4,500 lb. per square inchbefore it condenses to a liquid. On releas-ing the pressure on liquid CO, the gasrushee out and freezes to a white snow, thetemperature being - 80° C. As far as theproperties of liquid air are concerned, wecannot do better than refer to the article

interesting point was not raised although Ilooked carefully for it.

If a length of copper wire is cooled inliquid air, or better, to several degreeslower, its conductivity increases enor-mously-as a matter of fact, if you do thisat a temperature one or two degrees aboveabsolute zero, the conductivity of the metalitself becomes absolute-in other words itsresistance is nil. Thus, an electric currentonce passed along such a conductor wouldcirculate for ever.

The question is naturally, how to obtaina current of electricity in. a closed loop ofcopper wire ; obviously the method is byinduction. Consequently, an inductivelyexcited copper conductor would retain itsinduced charge for an infinite period, pro-vided it was at, or near, the absolute zero.Whether it will ever be possible to makesuch a conductor, we cannot say, but thereis no reason why an alloy may not be pro-duced in the future which will be far andaway more conducting at normal tempera-tures and pressures than those in everydayuse.

You can just visualise the great possibil-ities of a perfect conductor, where thetransmission of electric power is concerned.It would be quite unnecessary to resort tohigh tension in order to overcome resistance,while applied to dynamos and motors, justimagine the increased efficiency. Howeverit is a subject upon which it is premature tospeculate-there are possibilities, we know,but before they can be realised, untolddifficulties must be surmounted. Mentionof difficulties should bring to our memorythe stupendous job which confronted thepioneer workers in the isolation of raregases .and their liquefaction, and I thinkwe shall do well to consider their task incontrast with the novel method employedin the recent approach to absolute zero.

From Liquid Air to Absolute ZeroOn some past occasion, I referred to the

preparation of the rare gases, (PRACTICALMECHANICS, September, 1935) and themanufacture of helium was there shown tobe due to the extremely low temperature ofliquid air. Now helium was first liquefiedby a Dutch chemist, Kammerlingh Onnes,some years ago, after the gas was discovered

flask fame, did much research on the raregases, but was unsuccessful in his attemptsat isolating helium.

Hydrogen was liquefied more thanthirty years ago, and this was the last stepin the process of the liquefaction of helium,being only 15 degrees above the absolute.But 15 degrees is 15 degrees and so it hastaken some thirty years to come to thestage of helium liquefaction-a wonderfulachievement. That stage then, brought- usto within 1 degree of the absolute zero andthe overcoming of this 1 degree is a terrificand laborious job which may never beachieved, but what has been done is this.The magnetisation of certain crystal struc-tures causes a very slight increase in tem-perature, conversely, demagnetisationcauses a drop in temperature. Hence, if acrystal of this sort (a chrome -alum variety)is subjected to an intense magnetic fieldand cooled with liquid helium until thetemperature is at a minimum, while, atthis point the magnetic field is suddenlyremoved, a temperature three -thousandthsof a degree above absolute zero is attained.

Uses of Low TemperaturePerhaps the commonest use of low tem-

peratures is in the preservation of food-solid carbon dioxide being the most usualgas-fruit treated to such cold conditionsmay be preserved indefinitely, apples es-pecially benefiting. it is the object of theLow Temperature Research Station atCambridge to produce " new laid " eggs asa commercial proposition with the aid ofcold, but only moderately low temperaturesare necessary for food storage purposes,around - 40° C. Another important useis that of nitrogen manufacture from theair, a factor so vital in agriculture in thepreparation of fertilisers. Many otherchemical processes will benefit too.

A more recent use has been put to liquidoxygen. Those elusive particles whichaccompany the disintegration of atoms dueto beta -ray bombardment, the neutrons,are found to acquire far greater activitywhen cooled with liquid oxygen. Furtherresearch will no doubt show whether theseneutrons can be profitably used in radiationtechnique. Liquid air has been used inMedicine for the cure of insect bites, whilea very recent therapeutic use to whichsolid carbon dioxide has been put, is in thecure of leprosy, a report of which comesfrom Dorpat. The action of these lowtemperatures on the skin is similar to thatof intense heat-fulguration taking place,and it is too, rather difficult to localise anytreatment. In the case of leprosy, how-ever, the gas not only destroys the diseasealong with the surrounding tissues, butenables the essential bodies which counter

aire,aay IllentlelleCI, W111(41 was mu us anabout them. But unfortunately, one very

m la.Z1V11E ono in Idle rarer mmerma.Dewar, the English chemist of vacuum-

tne umease m Lne muou-anmoomee-I0be separated so that they can do their work.



A Handbook ofModern ElectricalPractice for the

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ACCUMULATORS AND BATTERIES.APPLICATIONS OF ELECTRICITY.-Industrial,domestic, medical, scientific, etc., as, for instance,Agriculture, Cinema Plant Refrigeration, Ultra -Violet Ray apparatus, Welding, etc.DEFINITIONS.-An essential group with hun-dreds of items.GENERATORS AND MOTORS. A.C. AND D.C.-Including large and small machines, from the32,000 kVA. alternator to the tiny fractionalh.p. motor with all accessory machines andapparatus.HEATING AND COOKING.-Every form ofmodern apparatus described with maintenanceand repair notes.INSTRUMENTS AND TESTING.-Meters of everyvariety now in use, faults and fault locationin cables, wiring, generators and motors, thebest methods of test, and testing instruments.LAW AND REGULATIONS.-Amply coveredand explained.LAMPS AND LIGHTING METHODS ANDFITTINGS.-Modern methods, such as LayLighting, Cornice Lighting, Tubular Lighting,Flood -lighting, and new apparatus, as HotCathode Lamps, fully dealt with.

MISCELLANEOUS: MATERIALS AND SPECIALDEPARTMENTS.-Every classification has itsmiscellany. Here are included the material.used in electro-technology ; specialist sectionssuch as electro-chemistry, electro-metallurgy,and other matters.SUPPLY AND TRANSMISSION.-The apparatus,principles, and methods employed between thepower station and the consumers' terminals.SWITCHGEAR AND SWITCHBOARD.-Theimmense variety of apparatus used for con-trolling electric power is covered in principaland detail.THEORY OF ELECTRICAL PRACTICE.-Putclearly and simply without incursion into highermathematics.TRANSFORMERS AND RECTIFIERS.-Includesevery variety of transformer, as well as MetalRectifiers, Mercury Arc Rectifiers, etc.WIRELESS OR RADIO WORK.-Discussionsof theoretical principles and their applicationin modern radio practice. Instruction is givenon repair and maintenance.WIRING: METHODS, MATERIALS, AND IN-STALLATION.-Including cables of all kinds,mid all the best apparatus and fittings.

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ROLL -FILM DEVELOPMENTMADE EASYBy G. L. Wakefield

An enlargement made from theminiature print in the left-hand

corner.

T0 the amateur photographer whodevelops a roll film only occasionally, adeveloping tank is an unnecessary ex-

pense. The job can be carried out quitesuccessfully in a small pudding basin, asshown in the photograph, and the resultsare as good as those obtained by morecomplicated methods.

Fast " chrome " or panchromatic filmsare best desensitised before development,when all the operations can be carried outin the light of a candle, or a bright yellowsafelight. The desensitising is done bysoaking the film for a minute in a dilutesolution of a special aniline dye, which hasthe property of making the emulsion muchless sensitive to light without affecting thelatent image.

There are several of such dyes obtain-able, and they can be bought, either intablet form, or in liquid, from any photo-graphic dealer. The use of such a dyeremoves one of the major difficulties fromdevelopment ; that of seeing when the filmhas attained sufficient contrast and density.

DevelopmentFor development you will need : a dish

containing the diluted desensitiser ; asmall pudding basin containing 6 or 8ounces of developer ; a bowl of cleanwater ; a dish with acid hypo bath.

Here is a suitable developer for all makesof roll film :

Metol . . . . 20 grainsHydroquinone . . 60 grainsSodium Sulphite (crystals). 14 ouncesSodium Carbonate (crystals) 14 ouncesPotassium Bromide . . 16 grainsWater to . . . 20 ounces

For use, dilute one part of developer withone part of water. If you have no facilitiesfor making up your own solutions, a chemistwill make up the required quantity for abouta shilling. The stock solution will keep formonths in a tightly corked bottle.

The acid fixing bath is :

Hypo . .

Warm water .

. 4 ounces20 ounces

When the hypo is dissolved, and thesolution cool, add 1 ounce of potassiummetabisulphite, and shake until dissolved.

Instructions for dissolving or diluting thedesensitiser will be found on the bottle orcarton. When all the solutions are in theirrespective dishes, unroll the spool of ex-posed film in complete darkness. Removethe backing paper, and run the film throughthe desensitiser, taking care to cover thewhole of it. If the film is held by one end

(Above) A finepiece of photo-graphic workand (Right)After beingdesensitised,the film can behandled in thelight of a can-dle, making iteasy to see howdevelopment is

progressing.

only, and raised and lowered in the dish, thefree end will wind up and unroll by itsnatural springiness. After a minute ormore in the desensitiser (according to themaker's instructions) transfer the film to thedeveloper in the basin, continuing the upand down movement's. The film should notbe rinsed between desensitising and develop-ment.

PrintingAfter two or three minutes' develoment,

the light can be turned on, either a candle ora yellow safelight, such as is normally usedfor bromide paper. Although the emulsionis now much less sensitive to light, it shouldbe treated with respect, and not placednearer than two feet to the light untildevelopment is nearly complete.

The density of the film can easily bejudged at this distance. From four to fiveminutes at a temperature of 65 degreesFahrenheit is sufficient for most films, butsome of the ultra fast panchromatic varietiesneed from five to six minutes at thistemperature.

When development is complete, rinse thefilm for a moment in clean water, and trans-fer to the fixing bath. Fix for fifteenminutes, keeping the film on the move.

Wash for a least half an hour after fixing.This is best done in a shallow hand bowl ;clip the film in a loop with a paper clip, theemulsion side outwards, and let the tap runslowly until washing is finished. As thehypo from the film sinks to the bottom iSfthe bowl, empty the water away every fiveminutes.

Before hanging the film to dry, wipe thefront and back with a piece of soft, wetchamois leather to remove any scum thathas collected from the washing water.



Models Ancient andModern

A side view of the finished model of the fire engine ready for the road.

MODELS, ancient and modern, were onview at this popular trade fair inFebruary, and drew much admiration

and discussion from the interested visitorsto Olympia.

There were three models of particularnote made by the well-known model -makingfirm of Bassett-Lowke Ltd., and exhibitedon their stand, which showed most clearlythe trend in modern craftsmanship.

The first, an li in. to the foot model of theRocket, was made for the Royal ScottishMuseum and standing alongside it was a

A view of the finished model showing the suction andoutlets of the motor pump.

working model of the L.M.S. express engineRoyal Scot. Both are to be same scale andthus represent an interesting comparisonin a century of railway progress.

The Rocket, finished in yellow and blackwith white chimney, is as originally con-structed by George Stephenson in 1829.It is in section and mounted on a piece oftrack, part of which is a replica of the

earlier type with stone sleepers, the re-mainder showing the later pattern withwooden sleepers.

Amazing DetailThe overall length of the model is 2 ft.

9 in., and it shows the amazing amount ofdetail of this pioneer model very clearly andattracted much attention at the Fair.

The work of making this museum typemodel occupied four skilled men over aperiod of three months. Most of the workwas metal work, except the tender, waterbarrel and boiler lagging, which was madein the wood -working shop. The unusuallyshaped tender wheels, engine trailingwheels, cylinders and wheel hubs were allmade from special patterns, and the frontwheels were built up in the metal hub, withwooden spokes and felloes, and a tyre ofmild steel.

A Difficult JobThe tender, body and barrel were made

from fine grain oak, the wheels of cast iron,and the fire box from copper. This wasbuilt by hand and has no less than 8510 B.A. steel stays in it, a very slow anddifficult job as these were all hand -made.The boiler barrel is made from sheet iron,the tubes of copper, and the correct numberof copper rivets are in all barrel joints.

byW. J. Bassett-Lowke,

M.I.Loco.E.

Some InterestingModels that were onView at the 1937 BritishIndustries Fair held at

Olympia

A model of the Dennis Dual Purpose fire engine, inthe course of construction, showing the escape nearlyfinished an some of the small parts of the motor in

the near foreground.

A 11 -in. scale working steam model o the Royal Scot exhibited at the British Industries Fair.



The smoke box is of copper, beaten by hand,the chimney hand -made in three slightlyconical sections, each fitting into each other,and the rods are made by hand from steel.Another very difficult but fascinating jobwas the making of the left hand cylinder,which was in cast iron, with the ports cast in.

The reversing gear is correctly modelled,

be used either as a stationary engine or as atraction engine.

Model Fire EngineLastly and 'probably most interesting of

all comes the exhibition model shown onBassett-Lowke's stand of an inch to thefoot Dennis Dual Purpose Fire Engine,

A view of the partly finished to the foot scale model of the Rocket and parts, in the course oconstruction.

giving forward and backward movementwith two eccentrics.

All bolts and set screws and nuts on thismodel are square, and the sectional part ofthe model shows half the number of firetubes, the tie rods to straighten the boilerends, the steam pipe and dome, and alsothe ferrules in the fire tubes.

An Interesting FeatureAn interesting feature on the front of the

model is the mercurial pressure gauge usedon early railway engines. The corona atthe top of the chimney was made in astraight strip from sheet metal, and thenrolled and bent into the correct shape.Two safety valves are fitted, one dead-weight and one spring loaded, as' specifiedfor the Rainhill Trials in 1829, for whichthis famous little engine was built.

The second model of the 4-6-0 RoyalScot, which became so well known fromits trip across America, is about 8 ft. long,fitted with steam brakes, and capable ofhauling anything between 10 to 15 pas-sengers on a 7} in. gauge Garden Railway.

A Traction EngineStanding in a special place of honour on

Bassett-Lowke's stand was a model of theBurrell Traction Engine that has alreadybeen described in these pages by Mr. F. J.Camm. This has already become a verypopular stock line and is complete withevery detail, embodying a regulator forspeed control, reverse lever for reversingthe model, pressure gauge, water gauge,steering wheel, and has a very fine water -tube boiler capable of maintaining a press-ure of 80 lb. to the square inch whenworking. This is definitely an improve-ment on any other Traction Engine on themarket, either at the price or even moreexpensive. A novel feature is that it can

finished in the vivid red of the L.C.C.London Fire Brigade, and the latest FireEngine in public service, and the Bassett-Lowke craftsmen were able to show theirversatile capabilities in modelling a fireengine.

The chassis was wrought in metal, mostlybrass, and the escapes and body constructedin selected wood with all the fitments,either in metal or wood carefully made inthe respective departments. The unpaintedmodel was completely assembled for theapproval of Messrs. Dennis Bros., and thentaken apart again, for plating and painting.The wheels are hand -made in metal withspecial rubber tyres, and the seats are up-holstered with leather spring cushions.The windscreen is of glass, and everythingfrom the tiny detail of the intricate pumpsat the rear to the large erecting wheels is intruth " realism in miniature."

Model Railway Exhibition

THE Model Railway Club, which twoyears ago celebrated its Jubilee, willshortly be holding its Annual Exhibi-

tion at the Central Hall, Westminster.Easter falling early this year, the Exhibi-tion opens on Tuesday, March 30th, andcloses Saturday evening, April 3rd.

All the four Groups of the British Rail-ways will be represented, each Group havinga large section to itself. Another largesection will be devoted to free-lancemodels, i.e. while not representing the rolling -stock of any British Group, still conformstrictly to Railway practice. There will beworking lay -outs in various scales andgauges where trains may be seen in motion,controlled from a central point, and allfaithfully carrying out real practice inminiature.

There will also be a section composed ofModels of historical railway interest, andanother of antiques of railway interest onloan to the Club. Altogether this Exhibi-tion should not be missed, and no one pay-ing the Club a visit will for a moment regretdoing so, on the contrary, he will probably

A photograph of the finished model of the Rocket showing the side of the engine fully modelled.

Workers in both wood and metal wereemployed over eight weeks in constructingthis model, which contains every detailalthough it does not actually work.

be greatly impressed by what can be ac-complished by the amateur, and possiblyjoin the ranks, constantly growing, of themodel railway maker and builder.



The G.E.C. television receiver,showing the internal construction.

N the television section of the G.E.C.research laboratories at Wembley,Middlesex, is a room that is probably

the most dust -proof in the world.In this room is conducted one of the

most delicate operations in the manufactureof a television set. It is the spraying offluorescent powder on to the almost flatend of a glass tube which is to form thescreen on which the picture is produced.

It is this tube, known as a cathode-raytube, which is at once the most costly andthe most important part of a television set.

The tube is about 28 in. in length ; it iscylindrical in shape at the lower end, afterwhich it widens out into a pear shape, thebase (which in the finished set is the screen)having a slightly convex surface, althoughthis fact is not obvious to the viewer when

In the Cathode -Ray Tube the following funda-mental operations take place (see diagram) ;I. EMISSION OF ELECTRONS

This is obtained from an Indirectly HeatedCathode (C), similar in principle to that commonwith A.C. mains valves.2. FOCUSING OF BEAM

This is effected by means of an electric field (F)of such shape that it causes the divergent beamof electrons coming from the Cathode to be changedinto a convergent beam, in the same way as a beamof light passing through a convex lens. The focusingelectrode design has required long research intothe subject now known as " electron optics " andhas resulted in an exceedingly accurately focusedand bright spot.3. ACCELERATING THE BEAM

An electrode of high positive potential, called" accelerator " (or sometimes " anode ") (A.), isso placed as to give the beam of electrons anexceedingly high velocity (70 million miles perhour). The electrons thus acquire considerableenergy, which they give up to the fluorescentscreen when they impinge on it, thus producinga bright spot of light (S).4. DEFLECTION OF THE BEAM

The focused beam of electrons is made to traversethe fluorescent screen in both a horizontal andvertical direction by means of electrodes known as"electric deflectors" (X,%., Y1lT2). The focusedelectron image is displaced horizontally in therange of 6,000 to 10,000 repetitions per second(line frequency), and also vertically in the rangeof 25 to 50 repetitions per second (image frequency).

How a TelevisionScreen is Made

By F. GoddardAn Explanation of One of the MostDelicate Operations in the Manu-

facture of a Television Setwatching a trans-mission.

At the narrowend of the tube is acathode, fromwhich a stream ofelectrons is directedon to the screen,which, being coatedwith fluorescentpowder, lights upand thus gives apicture.

FluorescenceZinc sulphide is

the chemical mostcommonly used tosecure the fluores-cence, but there are

other compounds mixed with it. The pro-portions of these must be accurate withinone -thousandth of one per cent.

Actually, different mixtures give slightlydifferent tones of colour to the picture.The G.E.C. were experimenting on thispoint for a considerable time before tele-vision transmission became regular. Agreat many different mixtures were triedout before the exact proportions at presentused were decided upon.

The spraying of the fluorescent powderon to the surface of the tube is quite as" finicky " a job as mixing it, for the layermust be absolutely even. It is for thisreason that the spraying is conducted ina dust -proof room. The slightest irregu-larity-even a particle of dust-woulddistort the picture.The Dust -proof Room

The dust -proof room in which thespraying is conducted has to be free, notonly of the kind of dust that the house -wifesweeps up in the morning, but of dust sominute that only the most powerfulscientific instruments can detect it.

MODULATOR

CATHODHEATER ACCELERATOR

FOCUSSING ELECTRODES

CONVERCINFIELD

The fluorescent powder is made to adhereto the tube by the use of waterglass.

The speed at which the screen is bom-barded with electrons is 70,000,000 milesan hour. The cathode-ray tube, beingcompletely evacuated, has to be able tostand terrific strain. In order to combatthis strain the shape of the tube is mathema-tically worked out and each tube is sub-jected to a water pressure of over two tonsbefore being passed as perfect.

Between the cathode and the screen areseveral complex electrical devices, includingfocusing electrodes which act as a lens, anddeflectors where the tube widens.

These devices serve to deflect the raysfrom the cathode in such a way that theywill cover the whole screen.

Unlike a newspaper picture, which iscomposed of a large number of minute dots,a television picture is composed of hori-zontal lines. These lines are either 240or 405 in number, according to the systemof transmission used, and they are tracedat the colossal speed of 7,500 miles an hour.There is some danger of the picture beingdistorted by electrons re -bounding from thescreen after bombarding it. This dangeris eliminated by coating the sides of thetube with graphite.3,980 Parts

The cathode-ray tube is by no meansthe only costly item in a television set.To give an idea how true this is, the stan-dard 23 -valve G.E.C. set contains no fewerthan 3,980 parts ; the set which incor-porates an all -wave radio receiver containsan additional 2,000 parts.

The cathode-ray tube is, however, a veryexpensive item indeed to manufactureunder present conditions, although, forsome time before the B.B.C. began givingregular transmissions, the G.E.C. weremanufacturing sets on a regular produc-tion basis in the same way as the famousG.E.C. wireless sets are made.

EVACUATED GLASS BULB

ELECTRON SEAM FLUORESCENT

DEFLECTORS,FINAL VERT, NORZN,

ACC LERATOR

Cli M A, 3 Y3 Y, X,

Details of the cathode-ray tube.


392 NEWNES PRACTICAL MECHANICS April, 1937 April, 1937 NEWNES PRACTICAL MECHANICS 393

Fig. 1.-An exposed view, showing the secret V-shaped compartment.When the compartment is swung inside the box, the back of it becomes

the panel on the back of the box.

PEOPLE frequently talk about " thebox trick " as if there were only onetrick that could be done with a box.

Actually, boxes of one kind or anotherform one of the most valuable sectionsof a conjurer's stock in trade. By the useof ingeniously contrived false bottoms,flaps, secret linings, and other devicesboxes may be constructed to make articlesdisappear, change into other articles,multiply, appear, change colour, in fact doalmost anything that looks as if it couldn'tbe done.

For Producing ArticlesFig. 1 shows a view, which the audience

naturally are not allowed to see, of a boxdesigned primarily for producing variousarticles after the spectators have seenthat it is empty. Some conjurers use abox of this kind to introduce magicallythe various things required for theirtricks, casually showing the box emptynow and again, but always finding in it theparticular thing they want for the nexttrick, such as a handkerchief, ball, pack ofcards, and so on.

The box has a let -down front and ahinged lid. The back of the box, when itis shown empty, is actually the front of aV shaped compartment which in the

m ys TERIOW BOXES

illustration can be seen tiltedthrough the back of the box.When the box is closed, thiscompartment is tipped insideand the back of the com-partment then becomes thepanel on the back of the box,as shown in Figs. 8 and 9.The box may now be turnedround to show all sides andwhen the lid is again liftedthe articles concealed in the

secret compartment are produced.By reversing the process anything that

can be tucked into the compartmentwhile it is within the box can, of course, bemade to disappear by tilting the compart-ment to the back. It should be notedthat the compartment is not the full widthof the box, a small marginbeing allowed at each side toprevent the audience seeinground the box and catchinga glimpse of the secret re-ceptacle. When performingwith an audience very muchat the sides, the conjurerholds the box with one handat each side so that his armshelp to mask the presence ofthe V-shaped compartment.

A Drawer in a CaseAnother very simple but

effective box is illustrated inFig. 2. This is simply a drawer in a case.The drawer is pulled out and shown to beempty, closed and opened again, and it isinstantly filled with toys, flowers, or any-thing the conjurer likes to put there.

In this case the secret is just an innerlining to the drawer. The drawer properhas no back and by means of a hole in the

Fig. 6.-End section of box,showing operation of flap.

Fig. 2.-The lining of the drawer containing the article to be produced,is here shown half -way out. Actually the front of the lining would Fig. 7.-Box with hole inbe close against the front of the drawer. Note the turned over edges removable base which controls the

of the drawer which hide the edges of the lining. opening and closing of the flap.

ing operationcage have been

__Sy Norman Hunter(The Wet/ -known Conjurer of Maskelynefs Mysteries Fame)

Clever ideas that Enable Conjurers

bottom of the casing, the lining may eitherbe held within the casing or be pulled outwith the drawer.

The box may be constructed of eitherwood or cardboard. Fig. 10shows the general principle. By r -inserting a finger of the handholding the case through thehole, the inner lining, into whichhave been packed the things tobe produced, is held back andthe outer drawer alone comesout. The front of the liningappears to be the back of thedrawer. To make all secure theinsides of the case, lining and

Fig. 3.-Diagram show -of sliding bottom. The wires of the

omitted for the sake of clearness.

drawer, are painted dead blackalso the outside of the lining.The drawer having been closed, it is onlynecessary to remove the retaining finger andpull out the drawer when the lining willcome with it, thus filling the drawer. Inthe illustration the lining is shown half-way out.

The LiningThe outer casing has a small strip of

Fig. 8.-(Above) The backof the compartment formsthe back panel of the box.

4

t

to clo the 4pparently Impossible

wood or cardboard along the inside of thebottom edge at the front, to butt againsta similar strip fastened to the under partof the back of the outer drawer. These

strips prevent the drawer beingaccidentally pulled right out.

Such a box will easily produceor vanish anything placed intothe lining. All that it is neces-sary to do is to hold back thelining at the proper time. Smallscraps of paper dropped into the

Fig. 4.-The cage being removed from the trick box.Note the sliding bottom which has here been held atthe top to show the position it occupies while the cageis in the box. It drops down as the cage is lifted out.

f

,,:ies4.,- -it5 4.-;-----7-,:. --r-"---- 7 - '

-.:.> --_i_

SLIDING BOTTOM6i;:-'2'(TO CAGE

Cf7GE

- -

Fig. 5.-An end section,showing inner lining and cage in position.

outer drawer can be changed to paperlanterns or dolls, or each scrap of paper maybe made to fill itself with a sweet. To dothis, fill the lining with wrapped sweets, showthe drawer empty as described, drop into theouter case a few wrappings taken fromsimilar sweets. Close the drawer, open itagain and there are your mysterious sweets.Needless to say, nothing bulky must be

Fig. 9.-(Below) An end section ofthe box, showing how the V-shaped

compartment swings in or out.

CCRET

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BOXCLOSED

BOX OPEN eAPPARENTLY

N. EMPTY PS111,, Y/E14/ED PPON1

PPONT

IIIPCUMPWRTMENTSECRET/ 5'14///155 TO

THE SPCA -

TAB EAW5L//VG L/AW5 TO BEFIELD L7PPPV5/7 /5I.C/Ll_ELP OL/7-

_ I

LORD I )

placed in the outer drawer orthe apparatus cannot beclosed or operated properly.

A clever method of in-creasing the effect producedby this box is to wrap somearticle, say a gollywog, in apatterned silk handkerchiefand conceal it in the lining.Show the drawer empty andplace a similar handkerchiefinto the outer drawer. When

the box is closed the empty handker-chief is crushed between the front of thedrawer and the lining and the gollywog,appearing in the drawer wrapped, ap-parently in the same handkerchief aswas just put into the box, makes avery puzzling problem indeed.

It should be noted that the top edgesof the outer drawer are turned inwardsto mask the edges of the lining (seeFig. 11).

Of Different ConstructionOf totally different construction is the

box shown in Figs. 12 and 13. There isno lid and the bottom is removable.The audience are allowed to look throughthe box, which seems to offer no pos-sibility of concealing anything, yet,when the box is placed on its base, which,by the way, may be of glass set in anarrow wooden frame, an incrediblequantity of silk handkerchiefs, flags,and similar articles may be producedfrom it.

Fig. 13 reveals the secret which is furtherexplained by Fig. 6. One side of the boxis hollow and is closed by a metal flap,hinged at the bottom inside the box andheld in position by a small turn button.The space thus provided in the thicknessof the box accommodatesthe load and, surprising as itmay seem, about twenty

Fig. 12.-A box with a removable glass bottom. The fingers ofthe hand holding the box are on the catch, ready to push it up and

release the secret flap.

handkerchiefs each eighteen inches square,if they are of fine silk, may be packedconveniently into the hollow side of a boxmeasuring about nine inches by six, thesides being half an inch thick.

In operation the box is held in one handand the base in the other. The fingers ofthe hand holding the box slide the turnbutton up so that when the box is placedupon its base the flap, forced by the loadbehind it, drops inwards and renders thearticles get -at -able.

The FlapsThe idea is often carried a step further

by providing the box with flaps to each ofits long sides so that a double load may beproduced. Another development is theuse of a wooden removable base having ahole in it. A finger of the hand holdingthe box may be introduced through thishole and close the flap from below asrequired (Fig. 7.) The box may thenbe used for a series of bewildering littleillusions ; a handkerchief is producedfrom the apparently empty box, vanishedand found in the conjurer's pocket (actuallya duplicate previously placed there).It is dropped back into the box and changescolour (the original handkerchief beingleft behind and one already in the secret

Figs. 10 and 11.-(Above) The lining left in the case and the drawer Fig. 13.-The box fitted to its removable transparent base and the flappulled out empty. (Below) The lining part of the way out, as shown in Fig. 2. released, showing the load ready to be produced.


392 NEWNES PRACTICAL MECHANICS April, 1937 April, 1937 NEWNES PRACTICAL MECHANICS 393

Fig. 1.-An exposed view, showing the secret V-shaped compartment.When the compartment is swung inside the box, the back of it becomes

the panel on the back of the box.

PEOPLE frequently talk about " thebox trick " as if there were only onetrick that could be done with a box.

Actually, boxes of one kind or anotherform one of the most valuable sectionsof a conjurer's stock in trade. By the useof ingeniously contrived false bottoms,flaps, secret linings, and other devicesboxes may be constructed to make articlesdisappear, change into other articles,multiply, appear, change colour, in fact doalmost anything that looks as if it couldn'tbe done.

For Producing ArticlesFig. 1 shows a view, which the audience

naturally are not allowed to see, of a boxdesigned primarily for producing variousarticles after the spectators have seenthat it is empty. Some conjurers use abox of this kind to introduce magicallythe various things required for theirtricks, casually showing the box emptynow and again, but always finding in it theparticular thing they want for the nexttrick, such as a handkerchief, ball, pack ofcards, and so on.

The box has a let -down front and ahinged lid. The back of the box, when itis shown empty, is actually the front of aV shaped compartment which in the

m ys TERIOW BOXES

illustration can be seen tiltedthrough the back of the box.When the box is closed, thiscompartment is tipped insideand the back of the com-partment then becomes thepanel on the back of the box,as shown in Figs. 8 and 9.The box may now be turnedround to show all sides andwhen the lid is again liftedthe articles concealed in the

secret compartment are produced.By reversing the process anything that

can be tucked into the compartmentwhile it is within the box can, of course, bemade to disappear by tilting the compart-ment to the back. It should be notedthat the compartment is not the full widthof the box, a small marginbeing allowed at each side toprevent the audience seeinground the box and catchinga glimpse of the secret re-ceptacle. When performingwith an audience very muchat the sides, the conjurerholds the box with one handat each side so that his armshelp to mask the presence ofthe V-shaped compartment.

A Drawer in a CaseAnother very simple but

effective box is illustrated inFig. 2. This is simply a drawer in a case.The drawer is pulled out and shown to beempty, closed and opened again, and it isinstantly filled with toys, flowers, or any-thing the conjurer likes to put there.

In this case the secret is just an innerlining to the drawer. The drawer properhas no back and by means of a hole in the

Fig. 6.-End section of box,showing operation of flap.

Fig. 2.-The lining of the drawer containing the article to be produced,is here shown half -way out. Actually the front of the lining would Fig. 7.-Box with hole inbe close against the front of the drawer. Note the turned over edges removable base which controls the

of the drawer which hide the edges of the lining. opening and closing of the flap.

ing operationcage have been

__Sy Norman Hunter(The Wet/ -known Conjurer of Maskelynefs Mysteries Fame)

Clever ideas that Enable Conjurers

bottom of the casing, the lining may eitherbe held within the casing or be pulled outwith the drawer.

The box may be constructed of eitherwood or cardboard. Fig. 10shows the general principle. By r -inserting a finger of the handholding the case through thehole, the inner lining, into whichhave been packed the things tobe produced, is held back andthe outer drawer alone comesout. The front of the liningappears to be the back of thedrawer. To make all secure theinsides of the case, lining and

Fig. 3.-Diagram show -of sliding bottom. The wires of the

omitted for the sake of clearness.

drawer, are painted dead blackalso the outside of the lining.The drawer having been closed, it is onlynecessary to remove the retaining finger andpull out the drawer when the lining willcome with it, thus filling the drawer. Inthe illustration the lining is shown half-way out.

The LiningThe outer casing has a small strip of

Fig. 8.-(Above) The backof the compartment formsthe back panel of the box.

4

t

to clo the 4pparently Impossible

wood or cardboard along the inside of thebottom edge at the front, to butt againsta similar strip fastened to the under partof the back of the outer drawer. These

strips prevent the drawer beingaccidentally pulled right out.

Such a box will easily produceor vanish anything placed intothe lining. All that it is neces-sary to do is to hold back thelining at the proper time. Smallscraps of paper dropped into the

Fig. 4.-The cage being removed from the trick box.Note the sliding bottom which has here been held atthe top to show the position it occupies while the cageis in the box. It drops down as the cage is lifted out.

f

,,:ies4.,- -it5 4.-;-----7-,:. --r-"---- 7 - '

-.:.> --_i_

SLIDING BOTTOM6i;:-'2'(TO CAGE

Cf7GE

- -

Fig. 5.-An end section,showing inner lining and cage in position.

outer drawer can be changed to paperlanterns or dolls, or each scrap of paper maybe made to fill itself with a sweet. To dothis, fill the lining with wrapped sweets, showthe drawer empty as described, drop into theouter case a few wrappings taken fromsimilar sweets. Close the drawer, open itagain and there are your mysterious sweets.Needless to say, nothing bulky must be

Fig. 9.-(Below) An end section ofthe box, showing how the V-shaped

compartment swings in or out.

CCRET

OM111.1147-44EW7-C'::7-5W//VG5 /NS/DE

BOXCLOSED

BOX OPEN eAPPARENTLY

N. EMPTY PS111,, Y/E14/ED PPON1

PPONT

IIIPCUMPWRTMENTSECRET/ 5'14///155 TO

THE SPCA -

TAB EAW5L//VG L/AW5 TO BEFIELD L7PPPV5/7 /5I.C/Ll_ELP OL/7-

_ I

LORD I )

placed in the outer drawer orthe apparatus cannot beclosed or operated properly.

A clever method of in-creasing the effect producedby this box is to wrap somearticle, say a gollywog, in apatterned silk handkerchiefand conceal it in the lining.Show the drawer empty andplace a similar handkerchiefinto the outer drawer. When

the box is closed the empty handker-chief is crushed between the front of thedrawer and the lining and the gollywog,appearing in the drawer wrapped, ap-parently in the same handkerchief aswas just put into the box, makes avery puzzling problem indeed.

It should be noted that the top edgesof the outer drawer are turned inwardsto mask the edges of the lining (seeFig. 11).

Of Different ConstructionOf totally different construction is the

box shown in Figs. 12 and 13. There isno lid and the bottom is removable.The audience are allowed to look throughthe box, which seems to offer no pos-sibility of concealing anything, yet,when the box is placed on its base, which,by the way, may be of glass set in anarrow wooden frame, an incrediblequantity of silk handkerchiefs, flags,and similar articles may be producedfrom it.

Fig. 13 reveals the secret which is furtherexplained by Fig. 6. One side of the boxis hollow and is closed by a metal flap,hinged at the bottom inside the box andheld in position by a small turn button.The space thus provided in the thicknessof the box accommodatesthe load and, surprising as itmay seem, about twenty

Fig. 12.-A box with a removable glass bottom. The fingers ofthe hand holding the box are on the catch, ready to push it up and

release the secret flap.

handkerchiefs each eighteen inches square,if they are of fine silk, may be packedconveniently into the hollow side of a boxmeasuring about nine inches by six, thesides being half an inch thick.

In operation the box is held in one handand the base in the other. The fingers ofthe hand holding the box slide the turnbutton up so that when the box is placedupon its base the flap, forced by the loadbehind it, drops inwards and renders thearticles get -at -able.

The FlapsThe idea is often carried a step further

by providing the box with flaps to each ofits long sides so that a double load may beproduced. Another development is theuse of a wooden removable base having ahole in it. A finger of the hand holdingthe box may be introduced through thishole and close the flap from below asrequired (Fig. 7.) The box may thenbe used for a series of bewildering littleillusions ; a handkerchief is producedfrom the apparently empty box, vanishedand found in the conjurer's pocket (actuallya duplicate previously placed there).It is dropped back into the box and changescolour (the original handkerchief beingleft behind and one already in the secret

Figs. 10 and 11.-(Above) The lining left in the case and the drawer Fig. 13.-The box fitted to its removable transparent base and the flappulled out empty. (Below) The lining part of the way out, as shown in Fig. 2. released, showing the load ready to be produced.



compartment removed instead). Thehandkerchief can then be multiplied intohalf a dozen which in turn may be changedto a flag, which eventually becomes ashower of flower petals. The changes aresimple, being effected merely by havingthe necessary articles packed into thehollow sides and producing them at theright times, leaving the other things intheir place.

Then there is a large box, about a footor more square, having a flap in each of itsfour sides. Such a box is usually made insections and put together in view of theaudience, after which the flaps are releasedone after the other and the articles behindthem are produced.

Producing a Bird CageIn Fig. 4 can be seen a box constructed

to produce a bird cage with a bird in it.The box is shown empty and articlesmay be placed into it, after which

a magic pass suffices to change thecontents into the bird cage seen in thephotograph.

The box has two lids and is constructedwith an inner lining, as shown in Fig. 5.The cage is bottomless and a separatesliding bottom is fitted which can bepushed up to within an inch or so of thetop, leaving just room for the imitationbird (Fig. 3). The cage fits over the innerlining of the box, the sides of the cagegoing between the outer walls of the boxand the walls of the lining (see Fig. 5).When the corresponding lid is closed, thebox may be shown, from the other end,and appear to be quite empty thoughactually the audience are looking intothe lining. The box having been filledwith whatever it has been decided to use,the lid is closed and the box turned com-pletely over in the act of placing it upon achair. When the box is again opened thenow uppermost lid is lifted and the cage

taken out. As the cage is removed thebottom sinks down into its proper placeand the dummy bird drops down andswings on its perch, being attached to thetop of the cage with string. The cageshould not be hung up, which mightcause the audience to imagine that it wascollapsible, but stood on the box, the lidbeing closed for this purpose. This notonly proves the solidity of the cage, butprevents any member of the audience fromcatching a glimpse of the lining, the closedend of which might now be visible to personsstanding or sitting near the performer.For safety's sake the interior of the boxat both ends should be painted deadblack.

A box like this is frequently used incombination with some other piece ofapparatus, the articles placed into thebox to start with, or rather duplicates ofthem, being reproduced from the othertrick property.

The New Unit Station development in 00 Gauge.

Latest Developments in ModelAT the British Industries Fair, Messrs.

Trix Ltd. were showing on their standa full range of samples of the new

" Many -ways " Station Buildings.These are made on the unit principle and

are very ingeniously built so that theymake up practically any form of station,either terminal, through or wayside. Thegoods depots, warehouses, engine andcarriage shed all have an excellent modernappearance. They have been designed byMr. E. W. Twining on the lines of themodern Southern Railway Stations nowbeing built.

Messrs. Bassett-Lowke Ltd. expect tohave these on sale in October next readyfor the winter season.

This season, a new method of packinghas been introduced. Single trams are now

packed in special Celilynd boxes with aspace provided for the other train whichmay be added later. With this innovation,of course, the great advantage is that youcan make a trial with one set of rollingstock without incurring the expense of twotrains.

We also note that Trix rails are now putup separately in their own boxes in a widevariety of complete formations, enablinganyone to choose with ease the track lay-out he most prefers. A well -illustratedbooklet, entitled " The T.T.R. PermanentWay Manual," is also included in each boxof rails.

Hambling's

Model railway enthusiasts contempla-

ailwaysting the building of a realistic minia-ture railway would do well to consider thepossibilities of the " 00 " gauge layout,with a track gauge of only in. A compre-hensive range of locos, rolling stock, andaccessories for this gauge is given in thelatest list (No. 52/1937) issued by A. W.Hambling & Co., 10, Cecil Court, London,W.C.2. The miniature locos are electricallyoperated, and complete electro-motors arelisted, and also separate parts of the me-chanism. A large number of blue -printsare also listed, giving particulars of variousdesigns of locos, permanent way layouts,and buildings. There is also an interestingrange of lineside and station accessorieswhich just give that finishing touch ofrealism. The list, which runs to 40 pages,is priced at 4d.



MODEL AIRCRAFT SUPPLEMENT

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In the April Issue-Now on Sale !* THE SKYROCKET PETROL PLANE

Third article of a series on constructing a record -holding Petrol plane.Designed by A. E. Brooks, this plane is an all-weather Hying certainty.Back issues obtainable, see back page April issue.

* "THINGS TO COME" FLYING SCALE MODELA large -size flying scale model of the Pterodactyl -type plane which was featuredin the famous film " Things to Come." Full-size plans.

* ALL THE CLUB NEWS * ESSENTIALLYUSEFUL HINTS AND TIPS, for the beginnerand the experienced

On Sale at all newsagents and bookstalls, price 6d., or direct fromthe Publishers, 7d. post free. The Model Aeroplane Constructor

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" THE NEW MODEL AEROPLANE MANUAL ""The most comprehensive book on the subject " 3s. 4d. post paid

The finest Designs, Kits, and Materials, etc., forbuilding successful flyers are described in

"THE PREMIER GUIDE" & FULL PRICE LISTSend at once to 4d. post paid

PREMIER AEROMODEL SUPPLIES2a HORNSEY RISE, LONDON, N.l9 'Phone: ARC 2376

FOR PETROLENTH USIASTS

The New British Baby, 2.3c.c. two-stroke engine, THE" SPITFIRE." A robust andyet midget engine that per-mits really small portablemodels being built. Thrust

lb., runs upright or in-verted. Petrol tank castingbolted on to crankcase, withreversible filler when engineinverted. Complete withcondenser, 1.4 oz. coil, etc.

Price / 4 / 0Carriage I/o.

mountings for Petrol Models.Send for our ART CATALOGUE.

Price 6d., Post Free.

TR "GLOSTER GLADIATOR

KITSBlueprints, cast props, and Gloster Gladiator, 16" span 5/6, carriage 6d. Hawker Fury,15r span 5/-, carriage 6d. Hawker Fury, 22' span 10/6.carriage 9d. Arrow Active Biplane, 24' span Mg, carriage9d. Leopard Moth, 22' sp. 7/6, carriage 9d. Completeand varied range of Kite, see our Catalogue, price 6d.

KANGA AERO MODELS I Colonnade Passage,New St., Birmingham

CALL AND SEE OUR DISPLAY, CENTRE OF TOWN, NEAR THEATRE ROYAL

HEALTHY MANHOODProfessor Caine's Curative Course (Illustrated), entitled "Philosophy of Health," tellsyou how to regain your vigour, how to stop excesses, overcome symptoms eman-ating from bad habits. This Course should be adopted by all who desire to escapefrom the thraldom of undesirable habits and obtain a Restoration of strength andhealth. It gives the Natural Method by which a restoration is obtained. Exercisesfor muscle building are given. Price complete 5/- Post Free. Sent strictlyconfidential:- Established since 1907.

PERCIVAL CARNE(PcHurTluCRAILsT) CRAHRIWDIBFIFNAs,w.

NORTHERN MODELSWish to introduce themselves to readers of " PRACTICALMECHANICS," and solicit enquiries for HO, 00, 0, or r gaugegoods. A large stock is carried and deliveries can be promptlymade. Our 00 EXACT TO SIZE Blue Prints with PLANare now adopted as Standard by the trade. Write for lists,

enclosing stamp to:

17, FRESHFIELD ROAD, HEATON MERSEY, Lancs.



THE NORTHERN MODEL AIRCRAFTESTABLISHED 191

THE OLD FIRMfor NEW LINES

We are not just importers ofAmerican Kits -our experience is asold as the Sport and Science of ModelAeronautics.

Our 1937 CATALOGUE and HAND-BOOK has been held up for theinclusion of lots of new lines. It willbe ready in early April. Nothing toequal this has ever before beenPublished.Sent to youpost free 4d.

37A FOUNTAINSTREET,

MANCHESTER

11 II II IIII

NEW ! Cherry -wood Pro-pellers for Power Models.Specially designed for variousengines. Small engines, 4 c.c., 12"& 122" diam., 3/6, 3/9. BabyCyclone, 6 c.c., 13" diam., 4/-.Brown Junior, 10 c.c., 14" diam.,4/4, all post free.

1937 Model Aeronautics YearBook, by Frank Zaic. 160 pages,83 plans, Petrol, Outdoor, Indoorand Gliders. 4/-, post 4d.

BOND'SGEARS.

\.rtf

Model Aeroplane Suppliesare

The Finest ProcurableAll the latest designs for the Wakefield Cup will requiregears. We make the finest precision involute cut gears onthe market. All will mesh together so that many ratioscan be made up. All gears are machined solid with thelarge boss and fit shafts.Brass wide teeth g" diam. diam. diam.

4d. 5d. 6d.Steel r wide teeth r diam. diam. f" diam.

3d. 3d. 4d.

WHEELS.Celluloid Balloon Type.

Diam. I" It" 1rPrice 6d. pair 8d. pair

Aluminium with Cork Balloon Tyres.Diam. I i" 21"Price 1/8 pair 2/9 pair 3/9 pair

1/- pair

3"

PROPELLERS. Special Lightweight Duration Props.Made of Light Basswood.

Size 6" 8" 10' 12' 14"Price 1/6 1/9 2/3 3/6 4/3

BALSA KNIVES. The perfect knife for cutting all Balsawood, etc.

Price 9d. complete.Spare blades 9d. for three.

BALSA WOOD Best Gradex r x 3 ft. 6d. r x r x3 ft. 8d. x fig" x 3 ft. Id,x x aft. Id. rx 3 ft. lid. r x x aft. lid.

I x 2r X I ft. I/. Other sizes see catalogueJAP TISSUE. Size 20" x 30" Price lid. sheet.BAMBOO TISSUE. Size 24" x 36" Price 4d. sheet.RUBBER. 1' x r Price 9d. doz. yds. 12" x r Price 1/2 doz. yds.DOPES. Clear, 6d. tin. Red, Blue, Silver, 9d. tin.BANANA OIL. Price 6d. tin.

Postage extra in all cases.We advise that wood should be cut into 18" lengths for safety.

Send for Bond's Illustrated 200 -page Catalogue. Price 6d., it will interest you.

BOND'S 0' EUSTON ROAD LTD.254 EUSTON ROAD, LONDON, N.W.I

Phone. EUSton 3780. Established 1887.

COMET KITS for Good Flights

GLOSTER GLADIATOR. Wingspan 18 ins. Length 14 ins. Auto -line-up Fuse-lage. Shock -absorbing Undercarriage. Very large clear plan, with all scale details,showing undercarriage works. The kit is complete :- balsa, shaped flyingprop, cement, silver dope, clear shrinking dope. Complete kit carriage paid

BRISTOL FIGHTER F2B.Wingspan 15 ins. Length 10 ins.Detailed plan makes a really fineflying model. Kit has everythingneeded, balsa, quick -dryingcement, shaped balsa flying prop,printed insignia, Japanese 2/tissue, etc. Carriage paid

HESTON PHOENIX.Wingspan 18 ins Length 10 Ins.Retractable landing gear withlocking control. The plan is veryclear. Comet Auto -line-up fuse-lage. Kit is absolutely 3/6complete. Carriage paiddi Send two Id. stamps for illus-

trated."' catalogue.

SEND YOUR

P.O. NOW10

P. M. SWEETEN Ltd.Bank Hey St., BLACKPOOL

11111111111111111111

M. S . S . VALUE KITSSCIENTIFIC, IMP AND

BUNCH KITSThese are outstanding examples of value: -

HI -FLYER, 20 -in. kits, 23 Models. Each .. 3/3Four new id-VaRtis have been added to the series. These haveMOVABLE CONTROLS, but price remain, the same : namely .. 8/8

New models are Hell -Diver : Monocoupe 90A Waco Fl and Waco Custom Cabin.

Flying Weather is Now Coming!BUNCH CADET, 20 -In. span, al ; 30 -in. open. 9/ -IMP KITS. 16.1n. span, 6 Models, V-.HI -FLYER De Luxe, 4 Modele,26.In. span. Ea.8/6" Mr. Mulligan" SCIENCE KIT, 25 -in. span,movable control., bridge type landing gear. Com-pletest Kit on the market. 9/-. The SplendidMONOCOUPE 90A, 60.in. span 80/-. New 1937'GWYN AERO" fi c.c. Petrol Motor 92/0Many Improvements. Now fitted piston rings,heavy duty points, etc. With special prop., 100/ -MODEL SUPPLY STORES (DeptManchester 3. And at 46

"MIGHTY MIDGET"eet ofparts, SW -prop. extra."MISS AMERICA" 7 ft. Gas Model Plane Kitfor above .. 57/0"RED ZEPHYR" 8 ft. Kit, equally suitable 42/6

All these Kits are complete in every detail.ACCESSORIES OP EVERY DESCRIPTION.Send 2d. for 18 -page Catalogue full of hints and

tips. Scores of Illustrations.Dealers apply for

P.) 4, Stewart Street, Deansgate,Derby Road, Prestwich, Manchester.

ECONOMIC ELECTRIC CO.TWICKENHAM,

SUPER MICROPHONESSensitive Broadcasting Micro-phones, with suspension hooksand rear terminals, 4/6 each.Complete with table stand, 10/6.TRANSVERSE PATTERN, inplated case, suitable for dancehalls. Price 48/- each. BUTTON

MICROPHONES 1/- each.

LONDON, S.W.SELENIUM CELLS

HIGHLY EFFICIENT CELLSfitted in round bakelite case,light surface r. Price 10/6each. Without case, 6/6 each.Square pattern, light surface10 sq., suitable for film or relay

work, 20/- each.

COMPLETE DEAF AID. Our new Aid, fitted with midget receiver,super -sensitive microphone, battery and switch, is equal in everyway to sets selling at £10/0/0. Our price is 42/.. You cannot do better !LIST. -Send for our Illustrated Catalogue containing 70 pages, fully illustrated, of all thatyou are likely to require -Meters. Motor., Telephones, Coils, Fitting., Transformers andparte, Lighting Bete, Tools and Workshop Material. It meta 6d. to print, but we send it

to you for 2d. post free.



PHOTOGRAPHS IN SOOTA Cheap and Effective Printing Process

with which all may ExperimentTHE printing process described in this

article is, perhaps, not quite theeasiest of photographic processes, but

it is certainly one of the cheapest, for, bymeans of it, the image con-stituting the photograph is builtup in ordinary soot or in anyother insoluble pigment whichthe photographer may care tochoose. Moreover, almost anyvariety of paper may be usedfor printing the photograph on,or, in place of paper, wood,and other smooth surfaces maybe employed.

Known as the " gum-bi-chromate process," this methodof photographic printing givesabsolutely permanent results,provided, of course, that thepigment used is itself a per-manent and unfadable one.Soot, which is merely carbon,is an exceedingly permanentand stable material. Hence,gum-bichromate prints madein soot or carbon are as per-manent as the paper or otherbase upon which they areprinted.

The gum-bichromate process is basedupon the fact that when a mixture of gumor glue and potassium bichromate is actedupon by light, the gum becomes insolublein water in proportion to the amount oflight action which it has received. If aninsoluble pigment, such as soot or finelyground carbon, is mixed with the bichro-mated gum, the pigment will remain on thepaper entrapped in the insolubilised gumand will thus form an image.Line Negatives

The gum-bichromate process works bestwith " line negatives," that is to say withnegatives which contain white lines onlyand in which there are no half or intermedi-ate tones. If we print an ordinary view orportrait negative in gum-bichromate, someof the finer detail will be lost. At thesame time, however, such a print willexhibit many striking and artistic featuresand, indeed, many photographic workersprint in gum-bichromate especially for thepurpose of subduing detail and obtainingthe peculiar rounded, soft -focus effectwhich is characteristic of the process when

used for the printing of ordinary negatives.In order to work the gum-bichromate

process we must start with the sizing of thepaper. Any variety of paper may be

Sensitising the paper with bichromate solution. .

selected for printing on, but, for thebeginner, ordinary plain white drawingpaper will be found the best. This issized by rubbing over it with a wad of

(Left) A finished printmade on ordinary draw-ing paper. (Above) Agum-bichromate print inordinary chimney soot.(Right) For developmentthe paper is floated oncold water, face down-

wards.

cotton wool saturated with a solution ofordinary cooking gelatine containing aquarter of an ounce of gelatine dissolved in3 ozs. of hot water. In order to preserve

the gelatine solution for furtheruse, a few drops of carbolicacid should be added to it.

Sensitising the PaperAfter the paper has been

gelatine -sized and. allowed todry, it must be wiped over witha cotton wool wad saturatedwith a solution of formalin ofthe strength oz. of formalinto 10 ozs. of water. Thisformalin treatment will renderthe gelatine on the paperinsoluble. The paper is allowedto dry, after which it maybe stored for subsequentsensitisation.

In order to sensitise thepaper make up a solutioncontaining oz. of potassiumbichromate in 5 oz. of water.Also, prepare a solution ofgum arabic by placing 1 oz. ofthe gum in a bottle containing3 oz. of water. In a few

hours, the gum arabic will have swollenup in the water, after which a gentlewarming of the liquid will suffice todissolve the gum completely. The gumarabic solution should then be filteredthrough muslin into an amber -colouredbottle and stored in the dark. If the gumsolution is to be kept for any length oftime a few drops of carbolic acid should beadded to it, otherwise it will go mouldy.

Having made up the bichromate and gumsolutions, we may now proceed to sensitiseand pigment the paper. These operationsmist be performed in artificial light andnot in daylight.

First of all, we saturate a wad of cottonwool with the biehrornate solution and rubit evenly over the surface of the sized andformalin-treated paper. The paper is nowallowed to dry, after which it is givenanother coating of the bichromate solution.The paper, after having been allowed todry again (it may be held in front of a firefor this purpose) will have a light orangecolour and will be extremely sensitive todaylight, but not to ordinary artificialforms of illumination.

Pigmenting the PaperNext comes the pigmenting of the paper

and this, at first, is apt to prove the only



difficult part of the whole process. Placeat the bottom of an ordinary cup abouttwo teaspoonfuls of the gum arabic solutionprepared as above, and stir into it a smallquantity of " clean " chimney soot. Inplace of soot, we may use lampblack, dropblack, vegetable black or, in fact, anyfinely ground insoluble pigment. We mayalso use for the same purpose the water-colour pigments which are sold in smalltubes for artists' use.

Whatever pigment we use, however, itmust be thoroughly ground into and mixedwith the gum arabic solution and the lattermust not contain too much of the pigment.The right amount to use in the gumsolution may be estimated by drawing a

brush charged with the gum over a portionof a sheet of newspaper. The newsprintmust be read clearly through the layer of thesolution painted over it. If the print isobliterated, however, then the gum containstoo much pigment and more gum arabicsolution must be added in order to lessenthe pigment content of the mixture.

Using the SolutionHaving obtained the right proportion a

flat camel's-hair brush is charged with themixture and is brushed over the bichro-mated surface of the paper, this operation,of course, being done in artificial light.As little as possible of the pigment mixtureshould be used, yet, at the same time, itshould be spread evenly over the paper.It will be found almost impossible to brushthe gum -pigment mixture perfectly evenlyover the paper surface and to avoid alltraces of brush marks. These, however,should be kept down to a minimum, afterwhich the paper should be put away in adark warm place to dry, a process whichwill take four or five hours. Paper sotreated will then be highly sensitive todaylight.

The paper is printed under the negativefor approximately one half of the timewhich it would take to print an ordinaryP.O.P. or self -toning paper under thesame negative.

DevelopmentFinally, comes' the development of the

paper, this being a process which necessi-tates the exercise of patience more thananything else. We require for the develop-ment of the paper a large flat dish of coldwater. The paper, after being removedfrom the printing frame, will be found tohave a slight image on it. It isfloated, face downwards, upon the surface

of the cold water, care being taken to seethat the paper surface makes propercontact with the water and that no air -bubbles are present on the paper. Develop-ment may take place in daylight, for oncethe paper is wetted it becomes insensitive.

The development of the paper will takeanything from one to twenty-four hours,and very little can be done to hasten it.Gradually, the parts of the gum layer onthe paper which have been unaffected bylight will dissolve away in the water,revealing the image which has been printedon the paper. If the paper had not beengiven a preliminary sizing with gelatine,the particles of pigment which now dissolveaway, would have become entangled in the

fibres of the paperand would refuseto come awayproperly, thusmaking it im-possible for a

clean " print to

Pigmenting the paper.Note the flat brush

employed.

be obtained. Here,therefore, we realisethe sole object ofsizing the paperwith gelatine and of

subsequently giving the gelatine layer onthe paper a treatment with formalin inorder to render it insoluble in cold water.

Must Not be TouchedDuring the course of the development, the

surface Of the print must not be touchedwith anything, otherwise the print will be

ruined. Towards the end of development,it may be permissible to stroke the whiteareas of the print (such as the sky) verygently with a very soft camel's-hair brushin order to remove traces of pigment whichobstinately adhere to the paper. Nothingmore than this, however, can be done toassist development. It is a question ofwaiting, until the pigment mixture on thesurface of the paper which has not beeninsolubilised by light action dissolves awayof its own accord.

Finishing the PrintThe print having been developed to the

satisfaction of the worker, should finallybe immersed for ten minutes in a solutionof common alum (containing, say, I oz. ofalum dissolved in 9 or 10 oz. of water) orin a solution of sodium bisulphite of thesame strength. This will remove anytraces of bichromate stain which may stillremain on the print and the alum will, inaddition, slightly harden the gum -pigmentconstituting the image of the print. Theprint is then immersed in two changes ofstill (not running) water and then allowedto dry without heat. The result will be aprint of absolute permanency and onewhich, if the processing has been reasonablycarried out, will present much charm ofappearance.

As previously remarked, the processwill not give very fine half -tone detail, butit will give a " rounded " image which,from an artistic viewpoint, is very effective.Negatives of black -and -white drawings,which are, of course, devoid of half tones,will be reproduced with great fidelity bythe process, provided that the negativeemployed is a vigorous or " plucky " oneand is not " flat " in character.

As an exceedingly flexible means ofobtaining artistic and absolutely permanentphotographic prints on a variety of differentsurfaces and as a very inexpensive mode ofprinting, the gum-bichromate process hasmuch to recommend it to the interestedamateur, particularly if he be of an experi-mental or artistic turn of mind.

NEW MILLION -VOLT X-RAYEQUIPMENT

A NEW X-ray equipment, designed tor-Igive a beam of higher intensity and ofgreater penetrative power than any so faremployed for the treatment of disease, hasjust been installed at St. BartholomewsHospital.

Remarkable in DesignThe X-ray tube itself is of very remark-

able design. It is 30 ft. in length andweighs 10 tons ! It consists essentially of along steel tube in which the filament andtarget are mounted and in which a highvacuum is maintained by continuously'operating oil vapour pumps. Only thecentral 12 ft. of the tube are contained inthe treatment room, the two ends projectinginto the two generator rooms which aresituated on either side of the treatmentroom. To prevent the spreading of theX-ray beam, the central portion of the tubeis surrounded by a protective sheath con-sisting of a 6 -in. layer of closely packedlead shot which is contained in two co-axial steel cylinders. An aperture in thesheath allows the transmission of the X-raybeam in the required direction.

In view of the great weight of the tube,it would not have been practicable to moveit to adjust its position over the patient, so

.11the floor of the treatment room was mademovable instead !

The Working VoltageThe voltage for working the tube is

derived from a step-up transformer whichgives 150,000 volts. By means of a specialcircuit employing columns of continuouslyevacuated rectifying valves and large oil -immersed storage condensers, a rectifiedcurrent of 600,000 volts may be obtained.The generating equipment is duplicated,and by connecting both sides in series, amaximum potential of 1,200,000 volts isavailable. At this voltage, the tube takesa current of 5 milliamperes.

The new equipment has been designedand manufactured by MetropolitanVickers Ltd., of Manchester, and it ishoped that it will prove of value in thefurther conquest of that dreaded disease,cancer.

* * * *

Television in Moscow

AN ultra -short-wave television stationis being built in Moscow. The aerial

is to be nearly 500 ft. in height in orderto ensure satisfactory reception within aradius of 40 miles.



BROWN Junior Aeroplane EngineThe petrol engine that " holds the field."A 10-c.c. engine of outstanding perform-ance. Weight with coil and condenser

1 11, ozs.

£6 I Os. Od.

Propeller 3 ozs.

12/6

The advantageof this metalpropeller is thatit can bestraightened ifdamaged andmade as goodas new.

Ask for Leaflet B.3, which givesfull specification.

Stuart Turner,Ltd.,

HENLEY-ON-THAMES

THE HALLAM " NIPPER " 6-c.c., rBORE,"STROKE. ILLUSTRATIONHALF SIZE. ENGINE COMPLETEWITH COIL, TANK, AND PRO-PELLER. WEIGHT 10 oz. PRICEK4.0.0. SET OF CASTINGS ANDPRINT, 10s. 6d. WE GIVE SERVICEOF SPARE PARTS AND REPAIRSBY RETURN OF POST. BRITISH

AND BEST.

SEND 6d. FOR CATALOGUEDESCRIBING 12 ENGINES AND

CASTINGS FROM 6 to 80 c.c.

J. HALLAM & SONENGINEERS,

POOLE - DORSET

BRITAIN'S BREEZIEST BABY ENGINE

THE SPITFIREWEIGHT ALL -ON 7 ozs., THRUST 4 lb.

£4 4 O.Complete with propeller, coil and tank.Everything for rubber and petrol models.

2d. STAMP FOR LISTS.T H E MODEL AIRCRAFT STORES1276 HANKINSON ROAD, BO URNEMO UT H

399

Budd youn own

IP E IR II1VAIL EMELTE otrumac mom

AMAZINGSUCCESS

BRINGS

HUGEPRICEREDUCTION

NOW ONLY

19'6CASH

Owing to the great successand the improved produc-tion facilities of this mostpopular hobby-we are ina position to pass on thebenefit to the public by re-ducing the price from 25/ -to 19/6. Hundreds of en-thusiasts have already builttheir own Electric Clock-have you made one yet ?Here is a wonderful oppor-tunity for you to obtain acomplete kit (nothing elseto buy) at the amazinglylow price of 19/6. Themost fascinating hobbythis year.

SPECIFIC ATION S KIT No. I.

Complete set of parts for movement, and metaldrum for enclosing movement. Coin Bronzedial, 5 ins. square-green chapters. Moderndesign hands finished in green. Adaptor, lengthof flex, screwdriver, oil and grease.

KIT No. IA.Same as above, but dial is punched with 4 holesin corners for mounting on cabinets, etc.

Complete parts with Coin Bronze dial 5 ins. square, with chaptersand hands in an attractive shade of green. Full instructionsand charts of parts given free with every kit-follow the simpledirections and you can't go wrong.No shocks-no soldering iron necessary. You can fit one to a table light, radio, table -bookstand, or you can use the clock separately as a Mantel or Boudoir Clock-thereare a number of places where you can put a PERIVALE Electric Clock, to increase theattractiveness of your home. When correctly assembled it's guaranteed to be anaccurate and reliable timekeeper for years. For A.C. Mains 200 v. to 250 v.

DON'T DELAY-GET YOUR KIT SET TO -DAY!KIT SET No. I and No. IA, 19/6

From your usual dealer and leading Stores. If unobtainable from your local dealersend P.O. or cash, plus 6d. postage, direct to

TheLONDON ELECTRICCLOCK Co., Props. G.M.T. Ltd.(DEPT. 14), 15 PARK STREET (OFF UPPER STREET), ISLINGTON, N.I.

North 3967. TRADE ENQUIRIES INVITED.

Bided yonh own

IP E IR OVALS. EmairEePrrnEuT cadesom



THE

BABY GNOME BROWN JUNIOR MOTOR1

REPEATED GOOD PERFORMANCE IN THE WINTER

WHAT WILL IT DO IN THE SUMMER ? ? ?Wing span 28 ins. - Total Weight 11 ozs.

COMPLETE CON- 6/6STRUCTION KIT

Construction Kit includes : Full-size working blueprint and instructions, allbalsa -wood strips and sheet, celluloid wheels and tube, cement, DOPE, tissuecovering, shaped propeller blank, wire hooks, bamboo, etc.SEND 4d. IN STAMPS (refunded with first order) FOR THE 1937GREEN BOOK, a complete list of our materials, all our Kits illustrated, comp.programme.

MODEL AIRCRAFT.SUPPLIES,.LTD.

Winner of the Sir John Shelley Cup Competitionheld by the S.M.A.E. at Fairey's Aerodrome, August, 1936.

Weight of engine 6 ounces Height above bearers 3115116"Wt. of coil, condenser and battery 7 ounces Width... ... 2i"Mimimum revolutions ... 500 r.p.m. Capacity ... 9 c.c. (i" x I")Maximum revolutions ... ... 6,000 r.p.m. Tractive effort ... lb.This very popular engine is suitable for any model with a wing span of 4 ft. to 10 ft.

Z6 - 10 - 0 COMPLETE,A.nl'aIsTrHequprRefjPELLER

OWING TO ITS WORLD-WIDE POPULARITY AS ARELIABLE AND LONG -WEARING ENGINE, IT IS

IDEAL FOR YOUR " P.M. PETREL "Come down to our shop and see one demonstrated. Open Weekdays till 7-1 o'clock Thursday.

SPECIFIED FOR THE "P.M." PETREL

THE GRAYSON "GNOME"3.5 c.c. Two -Stroke

L(a) Set of Castings, with Blueprint, in aluminium, 7(6; in electron, 10/6. lb) Setof Materials for fitting Engine, complete, 1/6. (c) Components (finished Parts):One Piston Ring, 1/6; Contact Blade and Points, 2/-; Lightweight (21 oz.)Coll, 101.; Lightweight (1 oz.) Condenser, 1/S; Sparking Plug, A.C., 1 in., 5/S;

Wood Propeller, 11 -in. diameter, 6 -in. pitch, 5/6.Sets (a), (8) and (c) together provide everything required to build complete Engine,

ready to run.Send for Booklet P.E., dealing with our larger model Engines, " Grayson" and" Grayspee." 3d. post free.

E. GRAY & SON, LTD.18 & 20 CLERKENWELL ROAD, LONDON, E.C.I

AM.offlength

"AEROBAT"BuiltatofpositionComplete

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our newclimb,shiftingWill

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designed

Folding Propeller, which,folds tight to the nose

centre of gravity to the correctto 5 minutes. Span 26 ins. gi- ' .Post free

Model-the "MOTH"in ONE HOUR ! 22 -in.

Practically crash -proof. - 'Post free 9p.

" BURD " I6 -in. span Flying Modelsas the other nine models 11/3

Post free liCatalogue, Just published.

WHOLESALE AND CLUBS SUPPLIED

ELITE MODELAIRPLANE SUPPLIES45 TAMWORTH AV., PRESTWICH, MANCHESTER

Dept. P. Prestwich 2671



Registration of ModelsI N view of the National Contest for

Petrol -driven Model Aeroplanes an-nounced elsewhere in this issue, and whichis bound to attract an enormous amountof attention to this most modem and mostrealistic of all types of model aircraft, aswell as to model aeroplaning in general,it is appropriate to mention that theS.M.A.E. are considering approaching theR.A.C. with a view to investigating theproblem as to whether models should notbear some designating number as with full-size aircraft. They are also consideringwhether it should not be made compulsoryfor petrol -driven models to be insuredagainst third -party claims. I do notsuppose that a petrol -driven model willever be responsible for serious damage,but it is wise on the part of the S.M.A.E. towish to look ahead and to circumvent anypossibility of legislation prohibiting theflying of such models altogether. Wemust remember that one or two localauthorities lacking vision, and unnecessarilyapprehensive of danger, are prohibitingthe flying of any type of model aeroplane.This is a short-sighted policy, and it isquestionable whether they have the rightto do it. A petrol -driven model can beflown under controlled flight conditions,as in our Contest, and it is no more dangerousto spectators than a cricket ball, a golfball, or a racing motor -car at Brooklands.The law is quite clear on this point. If aspectator unasked watches a cricket match,or a motor race, or a cycle race, or a modelaeroplane in flight, they cannot sue fordamage. I recommend the S.M.A.E. tocircularise the Clubs stating this point oflaw, which may not be generally known.

Petrol Model KitHAVE received a very well thought out

kit of parts for a petrol -driven model,which retails at the very reasonable priceof 3 guineas, carriage paid. It is suppliedby Comet Aero Supplies, Barwell, Leicester,and it has been specially designed for theBaby Cyclone Engine. The kit includesall of the necessary wood, glue, wire, wheels,instructions, drawings, silk, dope, part -finished chassis, etc. It may easily beerected and the whole model is of pleasinglines and well designed. The same com-pany tell me that they have designed andat present have on the test bench a British -made 3.5 c.c. engine, and promise tosubmit one to me for test. The specialair wheels which they supply in the kitreferred to above, or separately, havecompletely enclosed valves, and are ex-tremely well made and light.

Another New Petrol EngineMR. A. E. BROOKS, of the Air-

craft Stores, 127b Hankinson Road,Bournemouth, sends me details of anew engine which he has designed-the" Spitfire." This is of 14 mm. bore x15 mm. stroke, yielding a thrust of / lb.It runs upright or inverted. The cylindercapacity is 2.31 c.c. and consists of acasting in semi -steel close -grained, hard-wearing alloy, with an electron pistonfitted with a heat -treated molybdenumpiston ring. The gudgeon pin is of hollowsteel with soft copper end pads, whilst

liCIPIICSIBIY IF., J., C.,

the crank is. hollow and machined fromthe solid. The cylinder head, includingpins, are of heat -treated electron. Aninnovation is that the petrol tank is anelectron casting, bolted on to the crankcase,and fitted with reversible filler and deliverycaps, making reversal of the engine quiteeasy. The timer cam is of steel, and thecontact -breaker is adjustable. The coilweighs only 1 oz. energised by a 1 -oz. drycell. The weight of the unit, includingtank, coil, and propeller is only about7i oz. The price, complete with coil,tank, and propeller is 4 guineas, post free.The same firm are selling a number ofpetrol model kits at prices, includingengines, of £7 15s. (the Comet II), theComet Skyrocket at £13 10s., and theCalifornia Chief at £7 15s. They will senddetails to any reader. The accessoriesstocked by the firm include a 1 -oz. timeswitch, B.B. air wheels, and the B.B.flexible carburetter control.

Smith, 1 Treen Avenue, Barnes, S.W.13.All other matters should be addressed toMr. E. F. H. Cosh, 35 Maple Crescent,Sidcup, Kent. There are now over 30Clubs affiliated to the S.M.A.E. A largenumber of enquiries are being receivedfrom other clubs.

*

The Council of the S.M.A.E. recentlydiscussed the question of a standardisedbadge, and the delegates were requestedto place the matter before their respectiveclubs. * *

Mr. R. Copland, of the Northern HeightsClub, claimed a spar record of 18 min.52 sec. made at the Albert Hall on January22nd. This record was passed.

* *

The list of S.M.A.E. Competitions tobe held during 1937 is now ready ; theyinclude the Gamage Cup, the Pilcher Cup,the Model Engineer Cup, the Flight Cup,

The Gloster Gladiator made from one of the kits supplied by Messrs. F. P. Sweeten, Ltd.

Sweeten's New LinesMESSRS. F. P. SWEETEN, LTD.,

38 Bank Hey Street, Blackpool, havetaken up the sale of American solid kits toan exact scale of + in. to 1 ft. These kitsare excellent value, and incorporate a largeamount of faithful detail. The kit, whichincludes cement and coloured lacquers,costs only 2s. 6d. each. One of the newkits is the Gloster Gladiator, which buildsup into a really beautiful model, incorpor-ating a shock -absorbing under -carriage.It is of 18 -in. wing -span, and is excellentvalue for 5s. It is shown in the photo-graph.

The same company have developedtheir Ship Models, and now have four newkits at 4s. each-the Schooner Bluenose,the Cutty Sark, the City of New York, andthe Chinese Junk. The kits includedetailed plans.

The S.M.A.E. NotesWILL readers please note that all

enquiries concerning S.M.A.E. Com-petitions should be addressed to : TheCompetition Secretary, S.M.A.E., Mr. J. C.

the Western Cup, Cup for AutogiroModels, the Lady Shelley Cup, and theC.S.S.A. Cup, the Sir John Shelley Cup,Bowden International Trophy, theNational Cup, the Biplane Cup, FarrowShield, Premier Shield, and the WakefieldInternational Cup Contest. Copies of thelist will be sent to affiliated members.

The " Baby Gnome"ACOMPLETE construction kit for a new

outdoor superduration model has justbeen produced by Model Aircraft SuppliesLtd., 171, New Kent Road, London, S.E.1.It is a fuselage model of 28 -in. span, and itflies for at least 2 min. Its weight is only1k oz. The kit includes all balso woodstrips, tissue for covering, celluloid wheels,celluloid tube, gloss dope, rubber, cement,full-size blue print, instructions, wire, etc.

The model is of fine appearance, is welldesigned, and a guaranteed flier. Thesame company is supplying parts for manyother models, all of them listed in theircatalogue. They supply everything neces-sary for petrol and rubber -driven models-flying and scale.



EVERYTHING FOR THEAIRCRAFT MODELLER

The famous Selley Tex moulded kits. Practicallyindestructible. From 5/- to 23/-.

A " Burd always flies." Kits ranging from 1/3 to f1/1/0.Stockist for Scientific Kits. The very latest in flyingmodels. All movable controls. Kits ranging from

4'6 to 35:-.

A complete range of The Model Shop's Keelbild Kitsalways in stock.

AEROMODELS & AEROMINORSThe finest non -flying scale model aircraft on themarket. AEROMODELS i" to I ft. Kits, 3/6 to 7/6.AEROMINORS +" to I ft. Kits, 2/6 and 3/-. Postage

6d. on the large ones and 3d. on the minors.AEROMODELS and AEROMINORS can also besupplied ready built with customers' own markings.Minors 10/- each. Aeromodels from 17/6 to L2/0/0.

Carriage Paid.

Stockists for Megow's American Kits.Accessories of Every Description.

Catalogue sent on receipt of 3d. in stamps.

S. SMITH44, LEGH ST., WARRINGTON

LANCASHIRE

April, 1937

When up for the M.R.C. Exhibition( DO NOT FAILto visit our Showrooms, where you can discuss incomfort your problems and requirements.

We specialise in models for any gauge from " oo " tothe largest passenger -carrying railway.

You should see our multi -lever Frame, Brick Papers,Electric Signals, New Point Motors ; and don't forgetthat we do always have a stock of good used models.

Send for our beautifully illustrated Catalogue, 4d. post paid

MULTI - To00E1.5 L.48 BEAK STREET,REGENT STREET,LONDON, W.1

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H -O "CitiCo"MODEL RAILWAY ENTHUSIASTS - HALT !Before deciding, see what " CIMCO " haveMECHANISMS --The smallest Motor with the biggest

pull. Fit any H -O or 0-0 Loco. 4 -coupled, 26'6.6 -coupled, 32'6.

LOCOMOTIVES.-We can quote you for any modelPopular, Standard, or Super -detail Finish.F/l. 4-4-0 Express in all four groups . 65/-F/L 0-6-0 Tank . . . 63/ -

(Fitted with "CIMCO"mechanism.)TRACK.-Made up in Brass or Nickel Silver on solid

Brass Sleepers.24", 30", 36" Radii Curves and Straight in stockat : Brass, 1/9 ; Nickel Silver, 2/3. Plus postage.

WHEELS.-Specially die-cast in iron -hard metal. Largequantities in stock of 18, 21, 24, 26 mm. Drivers.1/6 per pair, including Squared Axle and LockingNuts.

LOCO., TENDER, and WAGON WHEELS (spoked) ofsame metal also delivered from stock, 6d. to 9d.per pair, on axle.

0-0LOOK !

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"CIMCO "also can offer DeferredPayment Terms andpurchases of LI andover. Write or call

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of 5/- or over.THE CITYMODEL CO.Showrooms & ServiceDept. : 37, Jewry St.,ALDGATE, E.C.3.'Phone : Royal 3658.

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STARGAZING FOR AMATEURSON the nights between the 5th, 6th, and

7th, and again between the 19th, 20th,and 21st, the Moon's terminator will

be in the vicinity of the fine lunar mountainCopernicus. If the weather is clear theseoccasions will afford excellent opportunitiesfor seeing the object under both afternoonand morning illumination. Copernicus isthe most perfect example of a ring formationon the visible surface ; and its statelygrandeur is enhanced by a comparativelyisolated position on a vast sparsely occupiedplain. Copernicus is nearly sixty miles indiameter and slightly hexagonal in shape.Its massive encompassing walls are toler-ably uniform in height and are surmountedby lofty summits, many of which tower12,000 feet above the interior. Both theouter and inner slopes of the giganticramparts are traversed by deep gulliesand terraced by well-defined ledges. Oneof the peaks of the central pile rises 11,000feet above the floor, and there are numeroushillocks and " craters " scattered about.The region surrounding Copernicus isribbed by low ridges pitted with circularindentations ; and, as the tide of sunshineadvances, a labyrinth of gleaning streaksappear, stretching in all directions forhundreds of miles. A map of the Moonis recommended as a guide to the " geo-graphy " of that weird globe. Messrs. Geo.Philip & Son, of 32 Fleet Street, London,publish one at 28. 6d. net.

The Elusive MercuryBetween the 10th and the end of the

month will be the best time during the yearto try and catch sight with the naked eyeof that elusive little world, Mercury.It will be at greatest eastern elongationon the 20th and for ten days before andafter that date may-weather permitting-be detected low over the western horizonglittering against the twilight like a yellow-ish star. At the beginning of the periodindicated Mercury will be a little belowand to the left of Venus. On the 12th itwill be not far beneath the young Moon.The planet should be looked for as soon asthe intense glare of sunset has somewhatsubsided. A binocular will help in thesearch, and a telescopewill show the phase tobe a miniature crescent.All endeavours toestablish the existenceof permanent markingshave hitherto failed.Various competent ob-servers claim to havenoted faint greyishpatches from time totime ; but these havebeen too vague andtransient to be reliable.A patient and pains-taking reader ofPRACTICAL MECHANICSmay nevertheless suc-ceed in placing thereality of some featurebeyond doubt, bycarrying out a longseries of carefulobservations. Materialthus accumulatedmight prove of theutmost value inarriving at the rotationperiod.

lS

A NEW SERIES

y N. de NultyA GUIDE FOR APRIL

The Smallest Satellite of the SunMercury is the smallest of the Sun's

nine important satellites, and also circulatesclosest to that luminary. It thereforerarely strays far enough out of the radianceof the latter (whether as a morning orevening " stair ") to be easily perceivedwithout optical assistance. The diameter.of the planet is only 3,000 miles-less thanhalf as much again as our Moon-and itsrelatively restricted orbit enables its " year "to be accomplished in but 88 of our days,i.e. under three months. The greateccentricity of this diminutive trackalternatively carries the planet from as near as 284 to as far as 434 million milesfrom the Sun. Consequent variations ofheat must be terrific, with a scorchingtemperature even at minimum. As alreadyindicated, the length of Mercury's day andnight cannot be conclusively ascertained ;but it is believed to coincide with that of its" annual " revolution. If so, one hemis-phere is continuously bathed in fierce sun-shine and the other perpetually steeped inglacial darkness save for the feeble glimmerof the distant stars and neighbouringplanets. The heat pouring down on thesunlit side is estimated to be at least650 degrees farenheit-hotter than themelting points of lead ! Some of therigours of the cold side may, however, bemitigated by warm currents flowing in fromthe baked one, if, as is thought, there is anatmosphere. A few authorities suspectthat Mercury may not really be a planet inthe ordinary sense of the term. Its physicalcondition and the abnormal eccentricity ofits orbit suggest that it might perhaps havebeen the solitary satellite of Venus which,at a remote period " escaped " from thegravitational tether of that now moonlessworld. But how it managed to wrenchitself free from the powerful attraction of solarge a body remains unexplained.

Sunrise on the great Lunar Ring Mountain Copernicus.

VenusVenus continues a brilliant " evening

star " in the first part of the month. It will,however, set earlier each night and soondiminish in lustre as it drifts back into theglare of sunset towards " inferior con-junction " between the Sun and the Earthon the 18th. It will then temporarilybe our nearest celestial neighbour, exceptthe Moon. Mars rises shortly before mid-night and may be found in the south-easttowards the early hours of the morning.It is rapidly approaching us and its reddishglow is brightening considerably. Jupiterrises about 3 a.m. and Saturn a couple ofhours later. Neither are convenientlyplaced for the amateur observer.The Great Bear

The well-known constellation Ursa Major(the Great Bear), popularly called thePlough or Charles' Wain, is almost over-head. It is actually a naked -eye clusteron an extended scale and consists of agroup of immense suns, most of which aremoving in space together. In addition tothe " Pointers," leading the eye to thenorth polar star, Ursa Major embracesseveral very interesting objects suitable forquite small instruments. Among them isMizar (E Ursa Majoris), a fine but closepair of twin suns associated with a quad-ruple system. It is the middle star of thethree forming the " tail " of the Bear.Adjacent to it is Alcor, much less con-spicuous and in olden days regarded as atest for keen vision. Alcor is an evencloser double than Mizar, but there is nophysical connection between them. Thereare numerous other double stars and nebulaein this constellation, the separation anddetection of which of course depend uponaperture and favourable atmospheric con-ditions. The most remarkable of thenebula is the " Owl " (M. 97), situated alittle below and to the left of the star 0Ursa3 Majoris, the lower of the " Pointers."It was so named by that famous astronomer,the late Lord Rosse, who, while examiningit through his mammoth reflector of 6 feetaperture, noticed two openings in thecentre with a star in the middle of each.

The curious effectproduced naturallysuggested the staringeyes of our familiarbird of the dusk.

TURN TOPAGE 366

FOR DETAILS

OF OURGREAT

NATIONAL

MODEL

AEROPLANE

COMPETITION



MODEL PRESENTS FOR EASTERA SELECTION FROM THE HUGE BASSETT-LOWKERANGE OF MODEL SHIPS, RAILWAYS AND ENGINES

SI-11PSiFnr:lsuhdef from theHni4d:l1124132473 Nii,?IrotIlealmraociiin.g. ...new modeal sf

fasttr stZersprwitet

balanced ... masts and brows in light rustless metal ... sails of union silk .. .

and the greatest power for sail area and length of any yacht at its size or price. R.2. White andGreen, 22 in. long, 45/-. R.3. White and Blue, 26 in. long, 57/6. R.4. White and Red, 3o in. long,92/6. Another skilfully constructed racer is the SOUTHWOLD, which costs 52/6, 19 in.overall : and 70/- 21 in. overall.IOLANTHE II. A new motor -boat improving on the famous BASSETT-LOWKE IOLANTHE I.With all the latest fitments and complete with mahogany cabin. Length 271 in. Beam si in.Fitted with permanent magnet motor running off dry battery or powerful clockwork mechanism.

Price, either type. 42/-.For those who wantto win races thissummer, build or buythe PRACTICALMECHANICS Fast

Motor Boat"Streamlinla."

Does 7 knots andruns for half an hour.Metre length. Writefor details.

MODEL SHIPSCatalogue S.12

6d. POST FREE

LOCOMOTIVES

L m s

Value in Gauge " 0 "-L.M.S. MidlandCompound-a useful and powerfulmodel for sharp curves. Smart and toscale. Clockwork 32/6. Electric d.c.

37/-; a.c. or spur drive 44/6.

SUPER DETAIL L.M.S. 4 - 6 - 2"Princess Elizabeth"

Model of the record -breaking L:M.S.Pacific accurately to scale.

Price, clockwork or electric a.c. or d.c.,(.8 . 0 . 0.

sa

IOLANTHE II

101_ ANT HE 13.

BASSETT-LOWKE LTD.have a special departmentfor the production ofSteam Locomotives from" 0" Gauge to 9f in.Gauge, either standardtypes or built to customers'special requirements.Easier manipulation andmaximum hauling capacityguaranteed with promptservice and moderateprices. Let BASSETT-LOWKE quote you for aspecial model to your own

specification.

SPECIAL VALUE IN PASSENGERROLLING STOCK

Gauge " 0" Bogie Corridor Coaches, specially designedand fitted with corridor connections. Length overall,13 in., in S.R., G.W.R., L.N.E.R. and L.M.S. colours andlettering, either brake 3rd- or 1st -class corridor. All thesame price, 14/6.

Fitted with turned cast-iron wheels, 2/- extra, and withscale bogies No. 612 with turned cast-iron wheels, 5/- extra.

HEATHERWHITE

YACHT

0-6-0 Good Locomotive-the latestaddition to BASSETT-LOWKE'S rangeof inexpensive locomotives of scaleappearance, in either L.M.S. orL.N.E.R. colours. Length 141 in.Clockwork 28/6. Electric d.c. 35/-,

a.c. 39/-. Spur drive d.c. 42/-.N.B.-If you are in London duringEaster, call at our Holborn Branch.We shall also be exhibiting at theModel Railway Club Exhibition, CentralHall, Westminster, from March 3oth toApril 3rd. See our Bargain Stand there.

1:25Atom-

, iirmiwainEiludgiumommivallrgU01.,GOODS ROLLING

STOCKFor many years BASSETT-LOWKEhave carried an enormous range oftinplate rolling stock of all companies.Here is their L.M.S. Open Wagonwith correct external detail. Gauge" 0." 51 in. long. Price 2/9.

Full range of Railway Productionsdescribed inA -I2 MODEL RAILWAY CATA-

LOGUE, 6d. Post Free.

FITTINGSFOR THEMODEL -MAKER

In addition to StationaryEngines and Boilers, theirSection 13.12 Catalogue(post free 6d.), containsdetails of thousands ofsundries for the model -maker. Boiler fittings,working drawings, cast-ings, and materials, nutsand bolts of every sizeand type.Illustrated is a Gun-metal Screw.down Wheel Valve. These,viith metal or black fibre wheels,4- in. cost 6/-, if in. 6/6,

in. 7/6.

The BASSETT-LOWKE new "TWIN TRAIN" LEAFLET T.T.12, free and post free, is now out.

BASSETT-LOWKE LTD., NORTHAMPTONLONDON : 112 HIGH HOLBORN, W.C.1. MANCHESTER: 28 CORPORATION STREET



A NEW TWIN -TRAINRAILWAY

UNIT

Fig. 1.-The chassis and motor unit of the newT .T.R. Southern Railway Electric Train.

THERE has recently been manufacturedand put on the market, in co-operationwith the Southern Railway Co., a very

excellent reproduction of one of thatcompany's electric unit trains in miniaturefor the twin -train system. This is sent out,boxed, with an oval track and controller,and sells at 558. It consists of one motorthird-class coach, one first-class corridorcoach, and one third-class corridor coach, allfinished and lined in the standard Southerncolours-green picked out with black andfine lined yellow.

Although the train is sold as a set withrails, etc., the coaches can be boughtseparately. Since, however, only the trainis new it is merely necessary to mentionprices of vehicles. The motor coach sellsat 308., the other cars at 38. each, and ofthese the following are available : first-classcorridor, third-class corridor, third-classbrake, and a restaurant car. Thus any readerwho is already in possession of twin -traintrack can add to his rolling -stock as he thinksfit. If he fancies the green coaches of theSouthern Railway he can quite well re -enamel one of his present locomotives tomatch.

The Motor UnitThis article is concerned chiefly with the

motor coach of the train. Readers willremember that in the issue of PRACTICALMECHANICS for March, 1936, I gave a draw-ing showing the motor mechanism of oneof the twin -train locomotives of steam out-line and diagrams of the electrical circuitsshowing the operation. The SouthernRailway motor unit is exactly similar ex-cept for the fact that the reversing gear isseparated from the motor. The coach is of

By E. W. Twining

A Model Electric Unit forthe Twin -Train System

Fig. 2.-The brushes and commutator side of the motor unit.

the double -bogie type and in this case themotor is mounted upon and drives onebogie whilst the reversing electro-magnetand the cylindrical commutator with itsbrushes is carried on the other bogie. Thetwo illustrations, Figs. 1 and 2, show bothsides of the chassis with the body of thecoach removed. Fig. 1 is the side of thechassis on which the reversing commutatorand ratchet is placed, whilst Fig. 2 is the

Fig. 3.-(Above) Ascale draw-ing of themotor coach

chassis.

commutator and brush -holder side of themotor. Fig. 3 is a scale elevation drawingof the former side of the unit.

Swivelling the BogiesSince I have previously dealt so fully with

the electrical gear it only remains for me toshow how the swivelling of the bogies isprovided for. As a matter of fact, beforethis train was produced the designing of it

was put into my hands andthe first difficulty whichcropped up was the necessityfor providing for the rotarymovement of the bogies. Obvi-ously, the usual bogie pins werenot practicable : the same motorhad to be used as in the twin -

B c train locomotives. In otherwords the motor on its wheelshad to be exactly as I showedin the drawing, Fig. 2, in Marchof last year, and there was nomeans of getting a stretcheracross either the bogie or themain underframes. The usualway of pivoting in such casesis by arranging a swivelling pinin the roof of the coach overthe motor, but I do not likethis arrangement, so I designedcurved guides D, with rubbingsurfaces E and stops B, thelast to prevent the bogie fromdropping when the coach waslifted. Fig. 4 is a plan view ofthe bogie frame and coach frame

Fig. 4.-A plan of one bogie showing the swivelling girders. only where the letters referred



to are repeated. In this plan nothing butthe frames are shown, but I would explainthat D and E are cast on the outside framesof the bogie which, for simplicity, have beenomitted from the drawing. In this plan Ais the main solebar or coach framing. ais the step running the whole length of thecoach and C the flat upper surface of thechassis which is of pressed steel plate.

Improved Design

The manufacturers have improved uponmy design in some details, though in themain the drawings which I now give hereare the same as I originally prepared. Imust say that the bogies swivel with perfectfreedom and without that objectionablesloppiness which is sometimes associatedwith carriage bogies of much larger -scalemodels than this. Fig. 5 shows a sideelevation and end elevation of the coach ;Fig. 6 is a photographic view showing bothside and end.

Owing to the fact that there were twobogies I was able to depart from the, it mustbe admitted, somewhat clumsy -lookingcurrent pick-up brushes which are soobvious in the electric locomotives, thosewhich rub on the outer or running rails.The brushes for the middle rail are on the

efficient manner than many so-called scale -model 00 gauge railways. For instance,has any one who has either manufacturedor made for himself a scale -model track everproduced a set of electrically operatedpoints which work as surely and as sweetlyas those supplied for twin -train working, or alocomotive motor which never fails until itis quite worn out ? I doubt it, and yet thatcan be justly claimed for the twins.

I will let the reader into a secret. Beforevery long curved track will be available ofmuch bigger radius than that now obtainableand then, probably simultaneously, we shallhave locomotives with wheel arrangementsup to the 4-6-2 or " Pacific " type.

Origin of the ScaleReturning to the matter of scale, I should

like to go back to the beginning of this small -gauge type of railway-a matter of aboutsixteen years. It was in the year 1921 thatMessrs. Bassett-Lowke, Ltd., produced asmall and cheap table railway which wasmanufactured for them in Germany. Itconsisted of an electric locomotive on fourwheels, a train of coaches and a circle oftrack made from pressed tinplate. Thesesets had an enormous sale. For the sake ofsimplicity the size was arrived at by making

April, 1937

must be equally to scale. When the muchlater Twin -Train Railway system was de-signed-and it was designed, be it noted, inGermany for German railway enthusiasts-the gauge was, for convenience, made thesame as the earlier table railway ; that is tosay, 16 mm. Moreover, the Germansadopted 3i mm. to the foot as the scale.So it will be seen that the Twin -TrainRailway is not 00 gauge as it has beenassumed, but is what has become knownas HO gauge.

An Important PointNow we come to the important point

which is, I take it, the one which some peoplequibble about. I have just said that thesystem was designed in Germany. Mostpeople know that the German loading gaugeis much bigger than the British. Let thecritic, therefore, measure up one of theGerman -made locomotives which are on theBritish market and he will find that theoverall width and height are correct for theGerman loading gauge on a scale of 3i mm.to 1 ft. " Oh, but," it will be said, " whenBritish locomotives were modelled thedimensions ought to have been altered."Well, perhaps this will come in time : thereis so much yet to come that when all the

I i

PI

*O1P(--ft

C 1 O--

1

11081 SOUTHERN RAILWAY --- 11081 _

......

l ) 1t

motor bogie as they are on the engine ofsteam outline, but those on the other bogie,although they press on one of the outerrails, are also placed on the centre line ofthe reversing unit bogie. This is done bymaking the stampings for the brushes pro-ject from the centre line out to the runningrail. The removal of one screw in the centrealone is sufficient to enable the brush holderto be turned around to pick up current fromthe other rail if and when required.True -to -scale or Otherwise

Now I want to say a few words aboutscale in connection with the twin -trainrailway system. It has been argued thatthere is no scale about the railway or itsrolling stock. I do not agree with this.Let me say at the outset that no one couldbe more fastidious than I am over exacti-tude in scale in a general way, but we haveto remember when criticising this systemthat it was produced to meet a certain de-mand-the demand for something whichwould sell at a low price, which would havegood general proportions, would work welland continuously and be capable of beinglaid for a little while and then put awayagain. I do not think that any one shoulddeny that it has met this demand admirably.Of course, this does not imply that it is trueto scale, rather perhaps the reverse; butthere is a scale underlying its design never-theless. Perhaps the chief point about thesystem is that it works continuously orwhenever it is called upon to do so, and I

Fig. 5. 5.-A side and end elevation of the motor coach.

it exactly half that of the standard 0 gauge.Now the width between rails of the0 gauge is 32 mm., or 7 mm. to 1 ft. Inthe simple table railway the width betweenrails was made 16 mm., exactly half of the32 mm. 0 gauge. It follows, therefore,that the scale of the gauge was 3i mm. to1 ft. The table railway made no pretence tobe more than a toy beyond the fact that thegauge was to scale. It must be admittedthat if 0 gauge is to scale, and so far as Iam aware no one has said that it is not, thenany railway which is exactly half that size

0 0 0

present schemes are realised and thingswhich are in preparation are marketed manypeople will be surprised, I can promise ; butat present with the existing motor thisdecrease in measurements of the locomo-tives to conform to British standards isimpossible because the highest points andthe widest points on the motor and reverseralready exceed the limits of the Britishgauge ; but I for one, although I am abeliever in true scale, do not carp undulybecause the engines look a trifle bigger andmore imposing than they ought to do.

must say it dces this in a more reliable and TFig. D. ne Southern Kaaway I.! .K. motor coach.



THE 1937MODELRAILWAYEXHIBITIONLocomotives, Coaches, Wagons, etc.

Working ModelsFree Rides Free Cinema Display

CENTRAL HALLWESTMI NSTER

MARCH 30th - APRIL 3rdTUESDAY : 2 p.m. to 10 p.m.Other Days : I I a.m. to 10 p.m.

ADMISSIONAdults 1/3 Children 6d.

(Incl. tax) (under 12)

Refreshments can be obtained at the Exhibition.

SPECIAL RATES FOR PARTIES, APPLY :-Hon. Sec.: 85 Wood Vale, London, N.IO

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(Left) : A view of the Jangfrau Railway and (right) the hiatus Railway.

0 144,C SV14 "Ho-apttata. . I

of the Swiss Federal Railways.

Travelling in Mountain Railways is aPassengers. There are Two Main Types in Use, Both of which are Described Below.

attway

HERE is no more spectacular achieve-ment of the modem engineer, than themountain railway, by which we can

ascend in safety and comfort to the verysummit of lofty mountains ; and no otherform of travel offers such thrills to thepassenger. I have travelled in aeroplanes,and also in an airship, but even when flyingat a great height, there is far less thrill thanI have experienced on the steeper sectionsof mountain railways, where the trainslowly ascends an almost vertical rock wall,with perhaps a sheer drop of a mile if any-thing goes wrong. But nothing ever does,for mountain railways hold the record forsafety, and the most nervous traveller hasnothing to fear.

Two Main TypesThere are two main types of mountain

railway, the rack and pinion, and thefunicular.

The first named consists of a track withthree rails, the two at the sides are ordinarysmooth lines for the wheels, but the centreone has a series of strong steel teeth, intowhich a cog wheel on the engine meshes,and so slowly winds the train up an inclinealmost as steep as a builder's ladder againsta house. The steepest lines are usuallybuilt on the funicular principle, that is theyare hauled by a steel cable. Frequently

particularly Thrilling Experience for the

Another view of the Jungfrau Railway.

such lines consist of a double track, so thata pair of cars can work together, and thedescending vehicle helps to draw the otherup. These are fitted with a centre rail onwhich the brake works.

If the thin steel cable extending up themountain above the car were to break, theautomatic brake would instantly come intoaction, and it can hold the train at thesteepest part of the line.

There is another form of funicular, usedwhen only small cars are needed. This isan aerial rope -way, in which a steel cable isslung from the top to the bottom of themountain on lofty brackets, and a small caris hauled up the cable by another rope.

The First LineSwiss Engineers lead the world in the

building of mountain railways, as is onlynatural. The first of such lines ever builtwas the Rigi line (there are now two).The line was completed in 1871, is 4} mileslong, nearly six thousand feet altitude atthe top, and an average gradient of 1 in 4.It is built on the rack and pinion system,and when first installed was hauled bysteam engines. Nearly all the mountain-railways now are electric, owing to thesaving in weight, and the cheapness ofpower derived from waterfalls.

The success of the Rigi line was enormous,



and quite a mountain resort has developedat the summit of the mountain. The Rigiis one of the easiest mountains, the slopesbeing mainly grass, without the dizzy preci-pices found on many other peaks, but thesuperb views from the summit make it avery popular ascent.

Boom in Mountain RailwaysThe success of the Rigi line soon led to a

boom in mountain railways, and more andmore are being built. One of the mostspectacular of the lesser mountains isPilatus, which like the Rigi, is near Lucerne,and is well known to English tourists.To -day this mountain is ascended bythousands of jolly holiday makers everysummer, but for centuries nobody dared toclimb the accursed peak, which-legendaverred-had been the grave of PontiusPilate. The story goei3 that in despairPilate committed suicide, but rivers intowhich the evil corpse was thrown rejected it.Finally it was taken up this mountain, andflung into a lake near the summit. If astone were thrown into this lake, a frightfulstorm would arise, and once a year thewicked Procurator appeared in a scarletrobe upon a near -by rock. And so forcenturies no one dared climb this wonderfulpeak, but in 1585 a brave Pastor did so,flung a stone into the lake, and daredPilate to come forth. This exploded thelegend, but it was not until the railway wasbuilt that tourists flocked to the top.

The line took two years to build, and wascompleted in 1888 by Locher of Zurich.The engineers who planned this daring linehad to scale dizzy slopes of nearly verticalrock, and to use their instruments whenslung by cradles from above.

The Jungfrau LineThe hardy mechanics who chiselled and

blasted the rocks worked under conditionsof great peril, which, of course, have beenfar exceeded by such later exploits as theJungfrau line. But even on Pilatus, asingle slip might mean death, a droppedtool, or a falling stone could sweep a maninto the abyss and workers had to be ropedon the more difficult stretches, though ofcourse parts of this line were quite easy.It is built on the rack and pinion system,the average gradient is 38 per cent. and the

A view of the Ritom-Piora line.

maximum 48 per cent. The centre -toothedrail has vertical teeth on both sides, intowhich two pairs of toothed wheels attachedto the train work horizontally ; the summitof the line is almost seven thousand feet.

The Trubsee cable railway near Englebergis a good example of this type of line. Twopairs of cables stretch from the top to thebottom of the mountain, and the cars areslung below the cable, and are hailed byanother rope. The maximum gradient isabout 68 per cent.

The Steepest LineProbably the steepest line in Switzerland

is the Ritom-Piora funicular, which ascends2,145 feet in j- of a mile, and has a maximumgradient of 87.8 per cent. This works on

journey takes 11 hours, which gives time toenjoy the scenery, and also for the humanbody to accustom itself to the vast changein atmospheric pressure. This preventsmountain sickness.

Into Eternal SnowsThe Jungfrau Railway is the most amaz-

ing of all mountain lines, for it boldlyascends into the region of eternal snows,and culminates at the dizzy height of 11,340feet that is more than three times as highas the loftiest peak of our own Snowdon.

few mountain railways have involvedsuch cost or trouble. It was commencedin 1897 by the eminent engineer Guyer -Zeller who died two years later. It wascompleted in 1912, and the cost reached the

The Engleberg-Trubsee cable railway.

the double -car principle, the descending carhelping to haul up the other. Cables areused for haulage the centre line seen inphoto is for the brakes. Note the pressurepipes beside the line, which bring waterfrom a high altitude to work the train.The photo of the little car well illustratesthe principle on which the trains have to bebuilt on steep lines. The seats are stag-gered one above another, like steps on astep ladder, if they were level-like theseats in an ordinary train-it would beimpossible to keep one's seat.

Two Remarkable RailwaysThe two most remarkable mountain rail-

ways in Switzerland are the Zermatt-Gornergrat, which is the highest open airrailway in Europe ; and the marvellousJungfrau line whose summit is the higheststation in Europe. These two lines arevery useful to the ordinary tourist, becausethey enable non -athletic people to enjoy theglorious scenery of these lofty summits,which few could hope to reach afoot.

The Gornergrat is a rocky ridge of theRiffelberg, 10,290 feet high. It has longbeen famous as commanding perhaps theworld's most impressive mountain view, achain of snow mountains dominated by thematchless peak of the Matterhorn. Therailway was finished in 1898. It is fit-ted with the Abt rack-and-pinion system,driven by electricity. The length is sixmiles, and the highest gradient 105. The

stupendous figure of £174,000 per mile-it is 51. miles in length.

At War with NatureThroughout the work the engineers were

verily at war with Nature in her sternestmoods. Portions of the mountain areswept by avalanches of snow, and fallingstones are a commonplace. The three upperstations, Eigerwand 9,405 ft., Eismeer10,370 ft., and Jungfraujoch are actuallyblasted into the rock itself-no outsidebuilding would have been safe in thatworld of snow, ice and tempest. Severallong stretches of the line are also tunnelledthrough the living rock, this is because asurface line would have been in continualperil from avalanches-huge masses of snowwhich sweep everything before them.

Perilous ConditionsThe engineers who planned this line, and

the hardy mechanics who executed thework, toiled under conditions of unimagin-able peril. On the upper parts of the lineweather conditions made work only possibleduring a few months of the year, and galesand snow were to be expected at any time.Workers were slung from cables with theirfeet dangling over infinity, while they hewedand blasted their way through the ruggedflank of the mountain. The lower part islimestone, and the upper is composed ofgneiss which is as hard as granite.

G.L.



J. L. McADAMApril, 1937

ROAD MAKEThe Man who First Demonstrated the Scientific Principle

upon which Every Durable Road is made Today

AT the beginning of the last centuryroads, as we know them to -day, didnot exist in this country. Travel

along the terrible tracks of the period wasalmost impossible during wet weather andduring dry it was so hazardous that it wasundertaken only when absolutely necessary.The country was composed of a number ofisolated communities so that a man waslooked upon as a foreigner in any districtbut his own. Thirty years later Britishroads were a shining example to the rest ofthe world.

This revolution was due to one man, who,though not an engineer by profession, firstdemonstrated the scientific principle uponwhich every durable road must be made.His name was John Loudon McAdam.

Roman RoadsWhen the Romans were recalled from

this country they left behind them a net-work of great highways running all over theland. But they failed to teach the Britonsthe elements of engineering so that theirthoroughfares immediately fell into a stateof disrepair. Indeed the Roman roadshave never been repaired to this day. Intheir place came rough winding trackswhich could be traversed only on horse-back. The social and material progress ofBritain was retarded for fourteen centuries.Trade in tin, iron, lead, lime, cattle, pearlsand oysters, exported in considerablequantities during Roman times, dwindledaway. The mud of Knightsbridge, for in-stance, was so great that it defeatedWyatt's rebellion.

The highways ceased to be the concernof the Central Government but were left tothe local parishes and Trusts. To obtainmoney for their upkeep, local authoritiesexacted tolls from the passers-by. Turn-pikes sprang up all over the country whichmade travel very laborious and very ex-pensive. The greater part of the moneyobtained from turnpikes went to the pocketsof corrupt officials.

Such was the state of the roads in 1756,when McAdam was born. He came froman old Scottish family and spent his child-hood days in Ayrshire where his fatherfounded a bank. At a tender age heshowed his interest in road construction bymaking a model of the route between twoadjacent towns.

He Loses His PropertyWhen John was fourteen his father died,

so being the only son, he was sent to livewith his uncle in New York. With theoutbreak of the War of American Inde-pendence John McAdam joined up with theBritish forces and when peace came he,together with all the Loyalists, lost all hisproperty. He decided that the best thingto do was to return to Scotland.

For fifteen years he lived in Ayrshirewithout showing any signs of the engineer-ing genius which was to make his namefamous the world over. But as he travelledabout he gradually began to realise thatwhat the country needed was some scientific,method of road construction.

Although he had never been trained as anengineer McAdam began to experiment on

John Loudon McAdam.

materials. He soon formulated his basicprinciple of road construction upon whichthe foundation of every modern highwayis built.

He reasoned that it was really the nativesoil which supported the weight of thetraffic and that so long as it was drainedand maintained in a dry state it wouldsuffice for this purpose.

To do this he laid the foundation of hisroads above the level of the adjacent

ground instead of digging a trench as wasthe custom at the time. Over this waslaid a layer of small stones about 6 in.thick.

An Amusing StoryMcAdam was very emphatic as to the

size of the stones for his roads and anamusing story is told on this theme. Beforethe introduction of the 2 -in. measureMcAdam used to tell the stonebreakers totry their mouths as a guide. If the stonewould not go into the mouth it was too big.One day he was examining a stretch of roadunder construction when he found stonesfar exceeding the limits imposed. Turningto a workman he angrily accused him oflaying the stones without testing them.The man stoutly denied the accusation andin support of this opened a mouth ofextraordinary size completely devoid ofteeth.

Under pressure of traffic the sharp anglesof the stones united into a compact masswhich kept the foundations absolutely freefrom water and frost which were the chief%causes of the breaking up of the older roads.

The arrival of the motor vehicle and itsrapid development as a means of transportwas to prove the soundness of McAdam'ssystem, though it brought the road engineerface to face with entirely new problemsThe first and perhaps most easily solvedwas the dust plague which quickly becamemost unbearable and detrimental to safety.In surmounting this particular dangerhighway authorities became widely ac-quainted with the possibilities of tar as aroad material and at the same time wereled to further discoveries of methods andmaterials which have since become of firstrate importance It was found that thetar which so successfully laid the dust alsohad qualities of much greater significance.It possessed abilities to bind the stone

A modem road in Germany.



materials on the road with a power sufficientto withstand the ever-increasing strains andstresses which came as the numbers of themotor vehicles doubled arid re -doubled.The demand for better and safer roadsdepended on its satisfaction for the furtherdevelopment of such materials andMcAdam's own cry for arteries fit to caterfor the great industrial life of the countrywas as nearly as possible satisfied.

His First AppointmentIt was not until 1816 that McAdam got

his first appointment as road engineer. Hehad been chosen as victualler of the Navyby the Government which necessitated hisremoval to Bristol. Here he managed tointerest the leading merchants with hissystem of road improvement. Eventuallythe Bristol Municipality approved of hisplans and invited him to take entire chargeof the 146 miles of roads as GeneralSurveyor.

When he was appointed, the roads in thedistrict were as bad as any in the countryand the Trust was heavily in debt. Ineighteen months he was able to report thatall his roads were in good condition, thathe had reduced expenses, increased theincome and had been able to pay off morethan £2,000 of the road debt. Bristol roadssoon became the best in the country and itwas not long before a Petition was sent toParliament pleading for macadamised roadsthroughout the Kingdom.

Others at WorkFrom that moment controversy began to

rage round his name. There were otherroad builders at work. Telford, a trainedengineer, insisted on a solid stone founda-tion and ridiculed McAdam's theory of anelastic soft base with a waterproof surfacemade with small stones.

London's streets were, at the time, quag-mires of water and mud so that the publicdemand for better roads became urgent.When it was proposed that McAdam's pro-cess should be adopted a storm of protestarose. But experience eventually showedhis theory was right.

Free of ChargeWithin two years most of the main thor-

oughfares of the capital had been macadam -

A modem macadamised road surface composed ofsmall stones welded together that the foundations are

kept absolutely waterproof.

A typical example of the modem and tarmacadam road.

iced and it was not long before all theprincipal cities of the Kingdom had followedLondon's example. During this periodMcAdam worked incessantly for his cause,travelling all over the country in answer tothe requests of numerous Trusts for aid andadvice. For this he received no paymentwhatsoever. " My belief," he said, " isthat if I had made it a money makingspeculation I should have strangled thebusiness in its birth and my system neverwould have been introduced in the countryat all."

Refused a Knighthood

So exacting did his work become that heasked his three sons to aid him. Togetherthe family laboured reconstructing roads,teaching others the new methods andbrushing away old forms of mismanage-ment and corruption.

In 1823 a Select Committee of Parliamentwas appointed to consider the work doneby McAdam for the country. Its decisionwas a triumph for him, but the oppositionto his methods of trained engineers wasstill so strong that it was only after con-siderable controversy that the recommenda-tions were passed by Parliament. As arecognition of his services to the countryMcAdam was voted a grant of £2,000. Afew years later he refused an offer ofknighthood on the pretext that he was tooold. Instead it was bestowed on one ofhis sons.

His Work Completed

In 1825, his work completed, JohnLoudon McAdam retired from public ser-vice to live in Hertfordshire till his death in1836. During this time he took a livelyinterest in the progress of the roads andwatched with satisfaction the rapid increasein the coach traffic which contributed in nosmall way to the position Britain attainedin the world's commerce during the nine-teenth century.

G. M. Trevelyan summed up McAdam'swork when he said, " Had it not been forhis roads the industrial revolution couldnot possibly have taken place, for therewould have been no means of transport tothe new markets that were indispensableto its increased production."

" Tips for Turners," by W. W. Watson. 79pages. Published by The Manual Press,price 2/6.

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Complete asillustrated.

LOUD SPEAKERCONTROL PANELA simple method ofcontrol forset and extension speakers andalso for headphones.

The Wireless World said :"A useful device for fitting toa receiver so that an externalloud speaker may be used inconjunction with the internalone, or without it, or the in-ternal loud speaker used alone,

tel has been evolved by LectroLinx Ltd."Practical Wireless said:" A useful device and a valuablesafeguard."Headphones greatly assist accuratetuning in of Short and Ultra Short-wave broadcasts. Use this Clix con-trol for easy switching over fromphones to speaker.

Easy to fit. Simple diagramshowing how to connect issupplied with each control.

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::':' jt;t:11?.i.,... er.174....::3;.....:a.,..tAk-rio4.-.S....;;-4 ......,-.7.-.r.,:t,... ,:".i.,,,4,,,,s,;*. 40:41-; :. ....;(*17,...o, 411.?:.i 1I

WIRELESS E PE IMENTERALTHOUGH the crystal receiver is

often regarded with scorn by thelistener with a powerful multi -

valve receiver, it has a definite field ofutility, and, in fact, to many listeners itoffers the only form of providing entertain-ment from the broadcast programmes.

A Stand-by ApparatusBut it may also be used by the listener as

a stand-by apparatus for use, for instance,whilst an accumulator is being charged, orwhilst a receiver is being modified. Fur-ther, it is the most satisfactory receiverto be constructed by the beginner, as it willlead the way to larger receivers and enablesall of the elementary principles to begrasped slowly. The old tag concerning thenecessity of learning to walk before youtry to run is very applicable to radio, and

Fig. 1.-A plan view of the finished receiver, toin wiring.

many constructors fail to make a satis-factory job of constructing a large receiver,simply because they have not commencedin a simple way. Primarily, the crystalset is a very simple piece of apparatus,consisting merely of a tuned circuit and acrystal detector, the latter being joined inseries with a pair of 'phones across thetuned circuit. But in such a form severaldifficulties would arise under modernconditions. The high power of the modernB.B.C. stations, coupled with the fact thatthere are, in most districts, two suchstations, renders it necessary to providea fair degree of selectivity, but as is now

THE P.M. CRYSTALRECEIVER

Details of anEasy - to -buildCrystal eceiver whichhas been esigned to Suitthe / e quir events if theModern

Listener.

assist

Fig. 2. -A three-quarterrear view of the receiver,showing the simple construction

and wiring.

well known, as soon as selectivity isintroduced, sensitivity automatically dis-appears.

The CircuitConsequently, a compromise has to be

adopted, and in a simple set such as acrystal receiver it is rather difficult tointroduce such a compromise. After con-sidering the results obtained with ordinaryreceivers in various districts, and analysingthe various requirements of listeners whowrite to us on this subject, we decidedthat a form of " adaptable " circuit wouldprovide the most satisfactory solution tothe crystal set problem. It is not satis-factory to design a standard arrangementand say that it will suit every listener in thecountry.

Reception ConditionsReception conditions vary in every

locality, and there are no benefits such asreaction which we can include in the circuitto make up for losses or to sharpen up the



tuning. The circuit finally adopted isshown in Fig. 6, and it will be noted thattwo of the components are shown in dottedlines. The reason for this will be givenlater, but it will be noted that a coil madeup of three separate windings is employed,and that a tuning condenser is joined rightacross it. The crystal is tapped to a pointa short distance from the high -potential endof the coil, and this has the effect of re-moving the damping exerted on the circuitand gives a slight increase in the sharpnessof tuning. The wave -change switch is ofthe double -pole double -throw type, andcarries out two functions.

The Wave -change SwitchIn the simplest form all that is necessary

to change from medium to long waves isto short-circuit part of the tuning coil, butthe same degree of selectivity is not re-quired on the long waves as is needed onthe medium waves, and thus it is an ad-vantage to be able to modify the aerialconnection when changing wavelengths.It will be seen in this circuit that whenin the medium -wave position the aerial isjoined direct to the top or high -potentialend of the coil (ignoring the dotted con-denser), whereas when switched over to

1937 CRYSTAL RECEIVERLIST OF COMPONENTS

One Paxolin Panel, 6 i n. by 6 in(Peto-Scott).

One Wooden Baseboard, 6 in. by 6 in.by # in. (Peto-Scott).

One Paxolin Former, 2# in. by 4 in.(Peto-Scott).

One " Formo Slow-motion Condenserwith Mystic Dial, type 511.5 (FormoProducts, Ltd.).

One Red -Diamond Crystal Detector(Jewel Pen Company).

One Component -mounting Bracket(B.T.S.).

One Double -pole Change -over Switch,type 1.23 (Wright and Weaire).

Two Terminal Socket Strips (Belling -Lee).

One 001 mfd. Tubular Condenser(T.C.C.).

Quantity 22 D.C.C. Wire, Screws, four4BA Bolts and Nuts.

The following additional componentsare required in some districts, asmentioned in the text :

One 0002 mfd. Preset Condenser(Formo Products, Ltd.),

One Anti -breakthrough Choke (con-structional details given in the text).

long waves, the aerial is transferred to apoint much lower down on the coil. Ifany doubt exists as to the advantage ofthis, the aerial should be removed fromthe aerial socket and connected direct tothe top of the coil in the long -wave position.It will be noted that a coil is shown indotted lines joined between the aerialcontact for the long -wave position and thetapping on the coil, and this is a specialanti -breakthrough choke which will befound invaluable to those listeners who aresituated close to a medium -wave broadcaststation.

Separating Two StationsThe condenser shown in dotted lines is

also of value to listeners in a similarposition as it may be adjusted to separatethe two local stations when a large aerial isemployed. Therefore, the receiver should

be first made up, ignoring these two com-ponents, and if it is found in your particu-lar case that the two locals are heardtogether, the pre-set condenser should beincluded between the switch and the topof the coil. Similarly, if when switchedover to long waves the medium -wavestation can be heard in the background, thespecial choke should be placed in circuit asshown in the wiring diagram.

Constructing the ReceiverThe construction is exceedingly simple,

and the components have been selected sothat no soldering is called for, and thus theset may be made up with only a penknifeand screwdriver. The panel and baseboardboth measure 6 in. by 6 in., and the formeris of paxolin. Ordinary three-ply woodmay be used for the baseboard, but a thick-ness of about f in. is desirable in order

Fig. 3.-The wiring plan.



that the panel may be firmly screwed to thefront edge. The panel may be drilled byfollowing the measurements and detailsgiven in Fig. 5, and the switch and terminalsockets should be attached. The variablecondenser is screwed to the baseboard, andthe correct position may be marked offfrom the wiring diagram, or it may beplaced upon the baseboard and the panelheld in position whilst the condenser is slidforward until the mounting bush comes intothe correct position. The holes should thenbe marked with a pencil and the panelremoved whilst the condenser is screweddown. Follow the maker's instructionsregarding the mounting of the specialslow-motion drive and scale.Winding the Coil

The coil is wound on a length of paxolintubing measuring 2-i in. in diameter and4 in. in length. Two small holes should bepierced at the upper edge and the end ofthe wire passed through, leaving a lengthof 5 in. projecting for connection to thevariable condenser. Wind on 8 turns andthen make a large loop-about 2 in. inlength, and in the position shown in thediagram of the coil. Continue the windingfor another 32 turns, and cut the wire sothat when passed through a further pair ofholes there will be approximately 5 in. left.About in. from this end of the coil makeanother pair of holes and pass the end ofthe wire through again, leaving a further5 in. for connection, and then wind on thewire, hank fashion, for 80 turns, afterwhich let the wire pass across the former fora quarter of an inch or so and wind asimilar hank winding of the same numberof turns. This will give you a grand totalof 200 turns of wire, the lower two pilesforming the long -wave loading coil. Thecoil is mounted by screwing a strip of woodinside the lower end. Alternatively, adisc may be cut from plywood for thepurpose.

Wiring the ReceiverNow note carefully, when ends of the

coils are connected to the respective points,and if the condenser and choke are to beleft out, the end of the first coil and thecommencement of the first of the two pilewindings should be twisted together and

In

6"

taken to the switch. If the choke is to beincluded, it should be joined betweenthe two switch contacts as shown. Notethat the end of the complete coil is joinedboth to the variable condenser and to theswitch, and the one length of wire may beused, scraping away the cotton coveringfor the purpose. The small fixed condenseris joined across the 'phone terminals, andthe crystal detector mounted on thecomponent -mounting bracket. The loopof wire in the first part of the coil shouldbe scraped and passed over the end of thedetector and locked beneath the terminalnut, whilst the lead from the detector tothe 'phone terminals is anchored betweenthe component mounting bracket and thelocking nut on the detector.

4"

The aerial should be provided with aplug and inserted into the aerial terminals,whilst the earth should similarly be con-nected. The 'phones are plugged into theright-hand pair of sockets. The condenserdial should be turned to tune in the desiredstation, and the small control knob on thedetector should be pulled out, turned andgently released when adjusting the detector.On no account turn this without pullingit out, as by so doing you will spoil thesurface of the detector and it will soonneed replacing. The particular type ofdetector used will be found sensitive inpractically every position, although it isworth while trying to find the most sensitivespot.

An Efficient AerialThe aerial should, of course,

be as efficient as possible, andin this connection height isthe most important factor.The insulation of each endshould be carefully carriedout, by using two or threeof the egg -type insulators,and the leading -in wire shouldbe brought down well clearof the house walls, guttering,pipes and other earthedbodies. Similarly the earthshould be as efficient aspossible, and a good soundconnection to a main water -pipe, through the medium ofa standard type earth clip, willbe found as good as any. Aburied plate or connectionto one of the proprietaryearths such as the Graham

Farish " Filt " may also be highlyrecommended.

8 lei,eno-

t /Ls32 Taencs

80 ruRNr.

go TuRNS

Fig. 4.-The coil iswound as shown here.Note carefully thatall turns are in the

same direction.

The Special ChokeIf the anti -breakthrough choke is found

necessary, it may easily be constructedfrom the same wire as is used for windingthe coil. Cut a disc of plywood about i in.thick and about 1 in. in diameter, and twodiscs of similar wood 1+ in. in diameter.Screw these together to form a spool anddrill a hole through one disc near the edgeof the centre piece. Anchor the wire inthis hole and wind 150 turns of wire inthe spool, afterwards anchoring the endof the wire through a further hole or by

wrapping a piece ofordinary tape roundthe coil of wire and

It

o

tying a knot.

For the BeginnerIf this is your first receiver, it is worth

while examining the arrangement of theparts and studying the relation betweenthe theoretical symbols in the circuitdiagram and the practical interpretationin the wiring diagram.

Place an Order with your Newsagentfor "PRACTICAL MECHANICS" to

be regularly delivered

Fig. 5.-Drilling diagram for the panel of the receiver. Fig. 6.-Circuit employed in the crystal receiver.



A Pendulum HarmonographA Device for Producing Complicated Curves, theRepetition of which make Attractive Patterns

4 N'NFig. 1.-The com-pleted instrument,showing the positionof the two pendulums.One pendulum carriesa small table at the top,and the other operates

a stylus or pencil.

THE harmono-graph de-scribed below

combines themotions of twopendulums to pro-

duce complicated curves of great beautyand regularity, and the autogmaticrepetition of these curves makes marvel-lous patterns. The number of differentpatterns that can be produced is incal-culable, in fact, it is in practice, impossible toget two alike. The apparatus is quite simpleto make and it is most fascinating to watcha pattern such as those illustrated herewithgrowing quite quickly before one's eyes ; theillustrations each took about one minute toproduce, and though it seems almost in-credible at first sight, each of them is madeby one continuous line.

The DesignsThe complete instrument is shown in

Fig. 1. The pendulum carrying the smalltable at its top end is mounted on gimbalbearings which allow it to move in anydirection, so that it is able to swing in circles,ellipses, or straight lines. The secondpendulum operates a pencil or stylus on theend of a hinged arm, and moves to and froin a straight line only, just like a clockpendulum.

Commence construction by making thebase board as shown in Fig. 2. It is in-tended that this should be screwed on to afirm table or bench, but be sure that there isno " ricketiness " about the support or theresults obtained will probably show wobbly,irregular lines. Screw clamps can be usedif it is not permissible to put screws into thebench or table. The two points are sup-ports for the gimbal ring-they are ordinarywood screws with a few threads filed off andthe remaining part filed to a nice point.Two small iron plates about in. thick arescrewed down one on each side of the

elongated hole, to carrythe pencil pendulum ; oneplate is recessed with thepoint of a drill and theother has a V -groove filedacross it.

The Gimbal RingThis is simply an iron

washer about -11- in. thick and 2 in. to2i in. diameter-the hole should beabout 11 in. to 1 in. diameter ; youwill probably have to file the hole out

it more convenient to use any other form ofweight make sure that it is rigidly attachedto the pendulum rod ; if it can wobbleabout it will probably spoil the results.

The pencil pendulum is shown in Fig. 5.The arm for the pencil may be attached bya couple of small brass hinges if you preferit, but the paper or tape hinges shown willprobably give better results as they are al-most frictionless and free from rattle.

The apparatus can now be assembled fortrial. Put the pencil pendulum weightabout half -way up the rod, and the other

z' -o"S

nxingScrews

It 3.> Ie I >k3

--Pi

Fig. 2.-The baseboard.

Fig. 4.-Theweightedpendulum.

if you use a standardwasher. Make a recess withthe point of a drill anddiametrically opposite tothe recess file a V -groove.Then turn the ring over and

do the same on the other side, but be sure tomake the groove and recess on one side on aline at right angles to those on the other (seeFig. 3). Do not try and make a knife-edgebearing for the gimbal, the arrangementdescribed is much simpler and better-unless the knife-edge bearing is made withgreat accuracy.

The PendulumIt is all made of wood except the weight,

which is simply a length of very stout leadpipe weighing about 1 lb., fixed with asingle wood screw (see Fig. 4). If you find

Fig. 6.-Thedesigns shownhere weremade with apendulum

harmonograph.

,..."13eCe5, onUpper Side

Groove onLower Side

Ciroove onUpper Side

Fig. 3.-The gimbal ring.

weight at the bottom to commence, and tryany other positions you like after. Youcan make a few trials with pencil and paperfirst, using a fine pointed pencil ; adjust thepressure on the pencil by arranging a smallweight on the arm-putting it on one sideof the fulcrum will, of course, increase thepressure and on the other side will reduce it.Set the pendulums swinging, drop the pencilon to the paper gently and watch results.

Y2 Die Rod 3 -0"Lon5

Fig. 5.-Thepencil pendulum.

"rapes 4) vect on



Smoked Glass for the DesignsAlthough pencil and paper are suggested

for a trial, far better results can be obtainedby using glass smoked in the flame of acandle, the line being scratched with thepoint of a needle. The needle should bepushed eye -end first into a piece of woodequal in size to a pencil, allowing only,about + in. of point to protrude. Theillustrations to this article were producedin this manner, and photographic printswere then made from the smoked glass

A further design made by a pendulum harmonograph.

diagram, which was used like a negative inan enlarger. Although the illustrations arethicked up somewhat in reproduction, theyare still much finer than can be obtainedwith a pencil. The needle, too, causesmuch less friction than a pencil, for theslightest pressure is sufficient for the needlewhile that on the pencil is considerable andthis causes the pendulums to die downquicker.

A Non -drip Bottle Stopper

THE novel stopper shown below, whichcan be fitted firmly into the mouth ofa sauce bottle by means of two prongs,

is capable of returning the drips back intothe bottle, thus keeping the outside clean.This is particularly advantageous, as thetop of a sauce bottle generally presents anunwholesome appearance after it has beenin use over a short period. As will be seen,when the top of the stopper is removed, aspring causes a nozzle to project past therim of the stopper, and any drips, insteadof running down the outside of the bottle,run down the nozzle and so back into thebottle when it is stood upright. Thedevice costs is. 6d. post free, and is obtain-able from H. L. Joelson, 86 Ealing Village,London, W.5. Please mention PRACTICALMECHANICS when ordering.

kV/REPRONGS

- L.ORDEDNOZZLE

CORKPYRSHER

A non -drip stopper which caneasily be fitted into the mouth ofa bottle, and (above) a sectionalsketch of the stopper showing the

construction.

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MN WIN MI MI IM MI MI MI NI NI



If a postal reply Is desired, a stamped addressed envelope must be enclosed. Every query and drawing which issent must bear the name and address of the sender and be accompanied by the coupon appearing on page 423.Send your queries to the Editor, PRACTICAL MECHANICS, Geo. Newnes Ltd., Tower House, Southampton

Street, Strand, London, W.C.2.

FINGERPRINT POWDER

"WOULD you kindly tell me the name

of the powder used for bringing outfingerprints on articles ?

" Is there any substance that readilydissolves phosphorus oxide fumes otherthan water, which is too slow ?

" Can formic acid be obtained from nettleleaves ? If so, how ? " (P. C., Surrey.)

1. THE best powder for fingerprintdetermination is lycopodium powder,

an inflammable yellow powder which con-sists of the spores of certain fungi. Gam-boge powder may also be used and, at times,the very finest air -blown talc powder.

2. There is no greater solvent of phos-phorus oxide fumes than hot water. Thewhite fumes of burning phosphorus are forthe most part composed of phosphoruspentoxide (P505) and this compound isexceedingly soluble in water.

3. Yes, formic acid can be preparedfrom nettle leaves, although the process istedious and the yield is small. Maceratea large quantity of nettle leaves with hotwater and finally distil the mixture. Aweak solution of formic acid will distil over.It cannot very well be concentrated byevaporation because the boiling point ofthe pure formic acid (101° C.) is too closeto that of water. You may, however,be able to prepare the pure acid from theweak solution by boiling up the latter witha quantity of litharge (lead oxide) until thelitharge ceases to be dissolved. Filter theliquid and then concentrate it to a verysmall bulk by boiling. Lead formate willcrystallise out. These crystals should becollected and placed in a bulb tube throughwhich dry hydrogen sulphide gas is passed,a small amount of heat being applied tothe lead formate crystals in the bulb.By the interaction of the hydrogen sulphidegas, and the warmed lead formate crystals,black lead sulphide will be formed and pureformic acid will be liberated. The latterwill be driven off by the heat and can becondensed in a tube cooled in ice -water.

A QUICK -BOILING KETTLEHAVE designed and made a quick -boil -I

ing kettle as per the enclosed sketch.Do you think I could patent this idea, orregister the design ?

" I made the model in copper, tinning theinside with ordinary tinman's solder. Doyou think this is perfectly safe to use in adistrict where the water is soft ? The localwater is obtained from the Severn, beingfiltered through sand beds and slightlychlorinated. It occurred to me that if thewater was slightly acid there might be a riskof small quantities of lead being dissolved,especially in view of the large surfaceexposed." (H. E. M., Worcester.)

THE improved quick -boiling kettle, ifnovel, is fit subject matter for protection

by Letters Patent. You are advised tomake a search amongst prior patent specifi-cations for kettles, before incurring anycost in protecting the invention. The ideaof utilising the spout of a kettle for fillingand emptying, is known to be old, and it isalso thought that the broad idea of employ-ing internal fire tubes is also old.

The exact exterior shape of the kettle, ifnot previously registered, could be regis-tered as a design, but such registrationwould not give any protection to the par-ticular interior construction.

It is not advisable to employ any lead -lined receptacle for boiling soft water forpotable purposes. In ordinary solder, leadis usually the preponderating constituent,it would therefore be advisable to employonly pure tin as a coating.

ELECTRIC LIGHT GLOBES" I WISH to make electric light globes

square in design, incorporating a patternin relief, and propose to cast or mouldthem with a white finish. Can you tellme if whiting or powdered chalk mixedwith stucco will give a white effect or will Ineed potter's clay. Perhaps you will knowof some other cheap mixture which I canmake up for moulding." (A. C., Glasgow,S.W.1.)

WE are not perfectly clear from yourletter as to the exact type of moulding

which you propose to employ. If you areusing a heat -moulding, you cannot employchalk as a whitening agent, since it changesin composition under the influence of heat.Whiting, however, would be quite adapt-able, as, also, would be magnesium oxide.Powdered alum and/or aluminium oxidecould also be used as white pigments.The admixture of potter's clay into yourmoulding composition will give a greaterbinding effect, but if its proportion in themixture is too great the material will beapt to be " grainy " and even to crumble.

PROTECTING A TRANSFORMER" I HAVE recently bought a 3 amp,

19 volt transformer for use on a gauge 0railway. Can you tell me how to protectthe transformer from short-circuits ? Ihave tried fuses, but they are not suitableas they have to be changed so frequently.

" Would a cut-out be of any use-if socan you explain the construction ?

" Can you give me the name of a firmwho can supply a cheap ammeter which willserve my purpose ? " (J. P., Ludlow.)

THE only satisfactory way to protect thetransformer in the case of short circuits

on the model railway track is to instal acut-out. Such a cut-out was described inthe article by Mr. E. W. Twining inPRACTICAL MECHANICS for March, 1936, onpages 352 and 354. See also diagramNo. 4 in Fig. 3.

As will be seen it consists of a solenoid,i.e. a coil having a sliding core, the coilbeing in the main supply circuit and thecore actuating a break switch which mustbe restored to normal position by hand afterit has come into operation.

WEATHER RECORDS" DLEASE could you inform me on the

f following, as I am shortly undergoinga test for a weatherman badge for scouts.

" 1. The wettest month on record ?" 2. The wettest day on record ?" 3. The extremes of temperature re-

corded, and dates ?" I wish these records to apply to the

Reigate borough, or failing this, for London."(R. M., Surrey.)

ACCORDING to the Meteorological Officethe following are the records required.

Wettest month, June 1903. 183 mm.Wettest day, June 28th, 1906. 60 mm.Maximum temperature, August 9th, 1911.

94° Farenheit.Minimum temperature, January 17th,

1881. 9° Farenheit.The foregoing are for Kew Observatory,

London. Period 1870-1936. Similardata for Reigate is not available.

COMETS" I AM very interested in the branch of

astronomy dealing with comets, andwould like information on the followingquestions.

" 1. Out of the 79 comets observedduring the period before Christ, the orbitsof four were calculated, namely, those of370 B.C., 136 B.C., 68 B.C. and 11 B.C., andof these four, only one was identified, thatof Halley's comet on its return in 11 B.C.As the book which contains this informationwas written in 1889, I thought that perhapsduring later years, more orbits of these 79comets may have been calculated. If thisis so, will you give me the date(s) of theirappearance(s) and if they have been provedto be apparitions of other comets ?

" 2. Will you give me the name of a goodup-to-date text -book dealing with cometaryastronomy, also the name and address of thepublisher, together with any other detailsneeded in order to purchase the same ?"(L. C., Walworth, S.E.17.)

NONE of the latest works on generalastronomy refer to the returns of any

of the pre -Christian era comets mentioned,except that of 11 B.c. (or 12), known asHalley's. Identification of even this onewas probably a matter of working back-wards. Observations of comets in thoseignorant times were too vague to admit ofaccurate determinations of their orbits andperiods.

We do not know of a book devoted en-tirely to comets. Most of those on generalastronomy give a section to the subject.For advanced mathematicians there isThe Calculation of the Orbits of Asteroidsand Comets, by Prof. R. P. Williams.(Principia Press Inc., Bloomington, Indi-ana). Price in this country, 15s.

COLOURED LAMPS" f -AN you please give me the formula

,...for making coloured lamp lacquer bothtransparent and translucent as is used onthe colour -sprayed lamps made by severalelectric lamp firms ? I require the trans-parent lacquer for lamps for indirect lightingand the translucent lacquer for lamps fordirect lighting, the lamps I propose coatingbeing the small ' fairy lights ' used fordecorating Christmas trees, etc.

" I have had a number of these sets in



use, and find that whilst the filaments arevery robust, the colours very soon bleachout of the lacquer." (P. L. P., near Leeds.)

YOU will be able to obtain the effects youdesire quite easily by preparing a thin

solution of celluloid in a mixture of ap-proximately equal parts of acetone andamyl (or butyl) acetate, and by adding tothe clear solution a few grains of an acetone -soluble dyestuff. In order to obtain atranslucent effect, the proportion of acetonein the varnish should be increased and aquantity of ester gum dissolved in the liquid.The precise quantity of ester gum to bedissolved depends entirely upon the in-tensity of the translucent effect required.

All the chemicals above mentioned maybe obtained retail from Messrs. A. Boake,Roberts & Co., Ltd., Stratford, London,E.15.

SELENIUM CELLS

"IN the March (1934) issue of ' Practical

Mechanics ' you gave details of theconstruction of selenium cells, particularly ofthe condenser type. The sizes you gavewere rather small and I was wondering ifit is permissible to use plates and mica oflarger sizes and thicknesses. Alternatively,could I use a sheet of mica clamped betweentwo supports and coated with selenium inplace of the condenser ? I have facilitiesfor sealing this electrode in a partial vacuum,so am wondering if this would be an advant-age or disadvantage to its working.

" My idea is to use this selenium cell formeasurements of colorometric chemicaltests. Do you think that the idea is feasible,using selenium in place of photo -electriccells, as the response to light need notnecessarily be instantaneous as sensitive.A sketch is enclosed." (E. F., Cardiff.)

THE selenium cell which you proposeto construct will probably function

satisfactorily, provided that you obtainthe selenium in the " grey " sensitive con-dition, but the cell would be rendered moresensitive if it consisted of a number of finecopper wires, wound in parallel formationover the mica sheet, the wires being clampedat one end of the cell. Such wires should beabout -inch apart and the entire surfaceof the cell (wires and mica) should becovered with a thin coat of the selenium.This, particularly in a partial vacuum-which will prevent atmospheric contamina-tion of the sensitive selenium-should beparticularly effective, provided that thewell-known selenium " time lag " is of noconsequence in your work.

The principle of colorometric chemicaltests by means of selenium cells is an oldone, having been experimented with beforethe war. Nevertheless, there is amplescope for research in this direction.

Plates of mica having larger dimensionsthan those given in PRACTICAL MECHANICSfor March, 1934, may, of course, be em-ployed, but with little or no real advantage.In a condenser type of cell, it is essential tokeep the plates as thin as practicable.

Your circuit sketch is incorrect. Aselenium cell requires a direct currentacross it and the current must be of steady,constant voltage which, usually is under60 volts. Such a current is best suppliedby means of a H.T. battery.

CHEMISTRY" COULD you give me some information

regarding the following :-" 1. What is the action of hydrochloric

acid on bleaching powder ? Please giveequation.

" 2. Why does hydrochloric acid fume inmoist air ?

" 3. Is the acid any stronger than nitricacid ?

" 4. Which halogen is the most active ? "(J. W., Newcastle 4).

(1)WHEN acted upon by hydrochloric

acid of medium strength, chlorineis evolved and calcium chloride is left insolution :-Ca(0C1)C12+ 2HC1 = CaC12+ 1120 +012.If, however, a bleaching powder solution istreated with very dilute hydrochloric acid,hypochlorous acid is first formed and thiseventually reacts with any excess of thehydrochloric acid to form water andchlorineCa(0C1)2 2H01 = CaC12 2HC10

(Hypochlorous acid)HM0 + 1101 = 1120 + 012.

2. Hydrochloric acid fumes in moist airbecause its vapour, as it were, dissolves inthe moisture of the air and thus rendersitself visible. These fumes consist ofminute globules of hydrochloric acid solu-tion.

3. Pure hydrochloric acid solution issomewhat " stronger " than nitric acid,yet nitric acid is a powerful oxidising agent,and this property, combined with its greatacidity, makes it, in many instances, amore corrosive liquid than hydrochloricacid solution.

4. Fluorine, a pale yellow gas, is by farthe most active member of the halogens.It is, indeed, the most active of all theelements.

ROCKET PROPULSION" I WOULD be extremely grateful to you if

you could inform me of the clause inthe Explosive Act of 1875, which prohibitsthe use of liquid fuels in rocket experimenta-tion.

" Liquid oxygen is obtainable at 7s. 6d.per litre. Do you think liquid air will becheaper than this ?

" Re the powder -fuels mentioned in theDecember issue of your paper. Does thisfuel need compressing ? I have madeseveral experiments with it and with mix-tures using more potassium chlorate, but Ido not seem to be able to get any propulsiveforce. The enclosed sketch shows the pro-portions of the nozzle, etc. Do you thinkthat the diameter of the nozzle is too great ? "(E. B., The Manchester InterplanetarySociety.)

1. THE explosives act can be studied atyour local police station or post

office. You must not use explosives inany manner likely to cause injury to per-sons or property and adequate precautionsmust be taken.

2. Liquid air, in small quantities, ispriced the same as liquid oxygen, i.e. about7s. 6d. per litre. For large quantities ofliquid air, a reduction might be obtainable.

3. The fuel powder does not need com-pressing. It should be " tamped " down,i.e. lightly rammed down in order to pre-vent its becoming too loose. The powdershould burn with a fair propulsive force,which, within limits, can be increased byaugmenting the potassium chlorate propor-tion of the powder. You do not actuallystate the nozzle diameter of your experi-mental rocket, and it is therefore difficultfor us to make a true guess at it from yoursketch. Generally speaking, the nozzlediameter should be just sufficient to give afree flow to the gases generated by thecombustion of the powder. In place of asingle nozzle, two, three or even more maybe tried. You will, no doubt, be able todiscover books on rocket construction in theTechnical Library, St. Peter's Square,Manchester.

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and by return you will receive a free copyof " The Science of Success," and particularsenabling you to enrol for a course of Pel-manism on specially convenient terms.

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PELMAN (OVERSEAS) INSTITUTES: PARIS, 8oBoulevard Haussmann. NEW YORK, 272 North Avenue,New Rochelle. MELBOURNE, 396Flinders Lane.JOHANNESBURG, P.O. Box 4928. DURBAN, NatalBank Chambers (P.O. Box 2489). CALCUTTA, 102Clive Street. DELHI, TO Alipore Road. A MST ERDA M,

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Things are happening to -daywhich vitally affect you!

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The most valuable employment securityto -day is the security a man creates forhimself-in himself ! Through training, heis able to adapt himself to new conditions,to utilise experience without being handi-capped by habit I He masters jobs andmakes new jobs. He meets emergencies-and is not overwhelmed by them. Andthis is an age of emergencies.

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DExaminations, state which

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Name Age

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COLD LIGHT"WITH reference to your article on`Cold Light ' in the January issue

of ' Practical Mechanics,' I would be gladif you could answer the following questions.

1. How is orthoaminophthalic cyclichydrazide prepared ? If possible I wouldlike to prepare some in a home laboratory.

" 2. Is it possible to alter the colour of thelight radiated by a luminous compound bythe addition of another salt ? If so, couldyou tell me the names of the most importantof these ?

" 3. In what oils is phosphorus soluble ?I tried warming phosphorus in olive oil,but although it melted, it did not seem tohave any appreciable effect. I used yellowphosphorus ; should it have been of thered variety ?

" 4. I am not quite clear as to whether theluminous appearance of putrefying fish isdue to the action of bacteria, or the spon-taneous combustion of minute quantities ofhydrides of phosphorus, given off by thedecaying flesh.

" 5. Some materials become luminousunder the influence of a radium salt. Doesthis apply to a uranium salt ? If so, whichsalts give the best results ? " (J. H.,Lincs.)

1. IT is quite impossible, from a practicalstandpoint, to make orthoamin-

ophthalic cyclic hydrazide successfully inan ordinary home laboratory, for the pre-paration of this compound from phthalioacid is a long and exacting process. Itwould be much cheaper for you to purchasea small quantity of the material. If youwill write to British Drughouses, Ltd.,Graham Street, City Road, London, theywill forward to you particulars of thiscompound.

2. The light emitted by luminous com-pounds may be varied somewhat by in-corporating traces of different impuritieswith the materials used in the making ofthe luminescent substances. Thus, forinstance, traces of manganese compoundsin calcium sulphide tend to impart a ruddyhue to the luminescence of the latter.Copper salts produce bluish and violentshades of luminescence, potassium salts,violet -white shades, and barium compounds,greenish hues. It is, however, impossibleto lay down the law on this subject, sincethe exact colour of the light emitted by aluminous compound is governed not onlyby the impurities in the latter but, also, toa certain extent, by the exact manner inwhich the luminous material has beenmade. Very little is known concerning theinfluence of impurities on the colour of thelight given out by a luminous compound.

3. Yellow phosphorus is soluble in oliveoil, turpentine, alcohol and other oils. Itis extremely soluble in carbon bisulphicle.We cannot understand why you wereunable to get the phosphorus to dissolvein olive oil. The oil, of course, must bewarmed. Red phosphorus is not solublein any of the usual liquids which dissolveyellow phorphorus. Incidentally, youshould be extremely careful when carryingout experiments on the solution of yellowphosphorus in oils, since such solutionseasily take fire, and, once alight, aredifficult to extinguish.

4. The luminescence of decaying fish isdue to the presence of luminous bacteriaand not to any phosphorus hydrides.

5. Only radium compounds and those ofits closely allied elements excite lumines-cence in other materials when the latter arebrought hear radium or radium -likesubstances. Uranium compounds do notpossess this power of exciting luminescence.

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FREE SERVICE FOR READERSREADERS requiring information concerninggoods or services advertised in PRACTICALMECHANICS should give names of Advertisersfrom whom particulars are desired. THERE ISNO CHARGE FOR THIS SERVICE.If any Advertiser stipulates that stamps or postalorders are necessary before samples or cataloguesare sent, please enclose the necessary amount withyour instructions.Post this7to

ADVERT. SERVICE DEPT.,PRACTICAL MECHANICS,

TOWER HOUSE, SOUTHAMPTONSTREET, STRAND, W.O.2

Please obtain and send to me particulars from the Adver-tisers in your April issue whose names I give on list attached,

Advertiser I Page No. I Information RequiredAttach sheet of paper, with particulars, and your nameand address (written in BLOCK letters) with date, to thisannouncement.



AMATEURSAN ADJUSTABLE BORING -BAR.

IN the making of any tool or applianceit is always best to use the simplestmethods for obtaining accuracy. It will

be seen from the drawing, Fig. 1, that theradial extension of the cutters B is limitedand fixed by the flared interior of the sleeveD and, as this sleeve has to be rotated onthe bar for the purpose of adjusting cuttersin the bar, it is necessary that the flaredinterior should always be concentric to theaxis of the bar. The drawing shows thesleeve held concentric to the axis of the barby a plain bore fitting on to a plain cylin-drical portion of the bar A. Now it isobvious that more accuracy and a closer fitcan be obtained for the sleeve on plainfitting than on a threaded fitting, and thatthis facility exists apart from the degree ofskill possessed by the constructor. It willalso be apparent that the production of acentral hole to house the coned spindle Cis difficult, if accuracy is required, and the

my-ikA.

which were faced flat on the inside for thesupport of the cutters B. This increasesthe support from being that of two points,to that of a line, and will not be so liable todamage from the pressure of the hardenedcutters B. To obtain substantial surfaceson the cutters at .K1 so that they may notdamage the flared cone of D, it is advisableto turn the faces K when they are inposition in the bar. This may easily bedone if the cutters are made with smallprojections K whereby the cutters can beheld as shown in Fig. 2, while the faces Kare being turned.

Making the BarThe procedure in making the bar would

be to take a piece of round Bessemer barof diameter just over the diameter of thethreads, place one end in the chuck and runthe other end in a steady. Drill andcounter -bore for centre, then reverse the

Figs. 1 to 3.-Details of the adjustable boring -bar.

hole may wander appreciably in the lengthrequired in spite of careful observance ofthe method given for drilling true to centre.It is, however, not necessary for the spindle

or its coned end to be true to the axisof the bar so long as both the cutters arepushed firmly to contact with the flaredend of the sleeve D. This feature can beensured by making the hole for C somewhatlarger than the spindle and then, providedprevious boring instructions are followedand the hole is reasonably near to truth,the spindle will have freedom to springsideways and impart equal pressures toeach of the two cutters B.

For Greater AccuracyAnother point making for simpler

production and greater accuracy is that thefalse centre F should be fitted into a plainbore and against a plain square face oralternatively as shown in Fig. 3 with theaddition of a threaded extension to preventit from being lost by falling out when thebar is not held between lathe centres. Itwould also help to maintain accuracy if thesleeve were made with projecting lugs G1

A

ArigrAdIAL0..."44

LL11111,..9

Fig. 3.

bar in the chuck and drill up the centrefor the required distance, preferably by themethod previously described, to Ittr-in.diameter, enlarge the bore of the outer endto about fin. diameter and face the endtrue to take the false centre as shown.Now bore a further recess of 11. -in. diameterto a depth of 2 in. for tapping Fin. standardWhitworth iron gas (19 T.P.I.) to take thethreaded portion of the spindle C. Nextscribe centre lines, mark out, drill and cutthe slots for the cutters B as previouslydescribed. Make and fit the false centre,adopting either of the methods shown andthen turn the outside diameter of the barbetween centres to the finished dimensions,screw cut the outer thread and tap Fin.standard iron gas thread internally for thespindle. Then fit the sleeve 0 with flatsfiled on the inside faces of the lugs in orderthat the cutters may have line bearing totake the pressure on these ends.

The SleeveThe screwed sleeve should now be made

from a piece of high quality steel as therewill be no possibility of hardening unless it

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TECHNICAL AND COMMERCIAL

RADIO COLLEGEFAIRFAX HOUSE,

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Post in unsealed envelope : ltd. stamp.! TO : T. & C. RADIO COLLEGE, II Fairfax House, High Holborn, London, W.C.1.I Please send me free copy of "Radio as a Career," in II plain envelope, and tell the how I can get well -paid

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MAXALDI NGtrresents

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showing his magnificent physique.He is the man who created historyby performing a perfect hand -balance on the centre of the bendingand swaying Carrick-a-rede ropebridge, at 100 feet above sea -level.He is a grand fellow and sportsman,performing for charity wheneverpossible. Note the superb develop-ment of the Serratus Magnus: thechief muscles of respiration, asexplained in the sensationalMaxalding announcement thatappeared in the January 9th issue ofthe "Passing Show."

His measurements are :Chest (normal) ... 40"Chest (expanded) 451'Waist 33" ; ... Neck 16"Upper -armForearm ... ... 13"Thigh 23" ; Calf ... 16"Height 5' 7"Weight ... 11 st. 10 lbs.

LESLIE McCURDY, performingEx. "M." of Maxalding, now known

as the Lung Builder.INVESTIGATE MA XALDI NGBy Postcard, Letter or Coupon. When Coupon is used,kindly delete the unnecessary items and post it, togetherwith the following particulars, to Mr. Saldo:

NAME, ADDRESS, Age and Occupation.

MR. A. M. SALDO (Dept. 88).14 CURSITOR STREET, LONDON, E.C.4

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can be ground afterwards. If hardening isdone and the sleeve is not subsequentlytrued, any warping will interfere withaccuracy, but an unhardened sleeve madefrom tool steel will give good results ifcare is taken not to over -tighten the conedspindle C and thereby press the hardenedcutters sufficiently to cause damage tothe flared mouth of the sleeve D whenlocking by the spindle C after adjustingthe diameter over the cutters B. Thecutters should be turned over the tops ofprojections K to make them both of equalcutting radius and the side faces could,with advantage, be machined at the sametime. It would be as well to mark the lugsof the collar G, say 1 and 2, and then tomark the cutters in the same way so thatminor errors of making do not causeinaccuracy by accidental reversal of cutterpositions in the bar.

FAIR COMMENT(Continued from page 372)

service. Some of those replies takean expert at least an hour, some evenlonger than that. We cheerfully meetthat cost but we do not charge thereader. Therefore, with a periodicaltake as your unit of value the chargesmade in other fields for advicewhich often is of the most trivial char-acter. Normally the information con-tained in one issue of PRACTICALMECHANICS alone would cost over £100.You get it for 6d., largely because ofthe enormous sales. As I said beforeit costs as much to set up an issue ofa periodical which sells only 5,000copies as it does for one which sells amillion copies. The more you sell thecheaper can the periodical be pro-duced within, of course, practicallimits, for it could never reach such afigure that you could afford to givethe copies away.

Value Given by a Periodical

F,for example, PRACTICAL MECHAN-

'es, appealed only to the restrictedmarket of 5,000 readers, in order to beprofitable, we should have to chargeat least 28. 6d. per copy. I ask you,therefore, to remember that if onlyone item in PRACTICAL MECHANICSinterests you each year, if a reply to aquestion solves some difficulty foryou, if a paragraph teaches you some-thing you did not know before, youhave been amply repaid for the modest6s. you pay for over 600 pages ofreading matter costing hundreds ofpounds each year. When you arecomparing units of value it is certainthat there is nothing in the worldwhich compares with the value givenby a periodical. It is not expectedthat every item printed in, say thisjournal, will appeal to you. It ap-peals, however, to some other readerswho are not interested perhaps in whatinterests you.

PRACTICAL MECHANICS 'Would becheap at double its price !

CONSIDER THESENVILCOFEATURES

Induction Motor. Bronze bearings. Constant lubrication. Silent and powerful. No interference with

radio.

1/10th H.P.This powerful motor develops 8,000R.P.M. It ie totally enclosed. Perfectfor driving sewing machines, small lathes,models. etc. Most useful power unit forany workshop. Reliable, smooth, quietrunning.Many other models listed In latest catalogue, 4d. post free.L. WILKINSON, 204 Lower Addiscombe Rd., CROYDON

Sold in 6d. and 1/- tins at all CycleAccessory Dealers, Tool Shops,

Ironmongers, etc.Write for your free copy "Joining of Metals" to

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TROUSERS MADETO MEASUREAny Waist fitted, 28 in. to 58 in.

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and width of bottom required.

5111 616 816Post 6d. or C.O.D.

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SPECIALISTS INTECHNICALILLUSTRATIONS

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BRITISH MADE.

BUY, EXCHANGE OR SELLAdvertisements are accepted for these columns at 2d. per word (minimum 12 words at 2s. -advertisements ofless than 12 words are charged at the minimum rate of 2s.), subject to a discount of 24% for 6 consecutivemonthly insertions or 5% for 12 consecutive monthly insertions. TERMS :-Cash with order. Cheques, PostalOrders, etc., should be made payable to George Newnes Ltd. The Proprietors reserve the right to refuse orwithdraw advertisements at their discretion. All advertisements must be received on or before the 5th of the monthpreceding date of publication and should be addressed to the Advertisement Manager, " Practical Mechanics,"

George Newnes Ltd., Tower House, Southampton Street, Strand, W.C.2.

CHEMISTRYCHEMICALS and apparatus. Elementary and

advanced. Bargain prices. -GRAY, 40 Grange Road,Lewes.

CINEMATOGRAPH YARTISTIC CINE FILMS. Exclusive 9.5 -mm.

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CINEMATOGRAPH FILMS. -Standard size from6d. 100 feet. Machines, Accessories. Sample Films1/- and 2/6 post free. Catalogues free.-" Fllmeries,"67 Lancaster Road, Leytonatone, E.11.

MOVIES AT HOME. How to moke your ownCinema Projector. Particulars free. Moviescope (N),Pear Tree Green, Doddinghurst, Essex.

ELECTRICALGOVERNMENT surplus Magnetos for making

dynamos. Bearings and magnets perfect. Small 5/6,large 616. Pulleys to fit, 2", 1/6 ; 3', 2/-. Wire andinsulation, from 1/6, carriage 1/6.-G. Briggs, Spring-field Electric Works, Brook Street, Preston.

A.C. MOTORS, DRILLS, all voltages. 1 -phase,60 cycles, H.P.8 : 1/100th, 15/9 ; 1/10th, 85/- ; 1, 49/9 ;1, 69/-; 1, 89/6. Electric Drills -1, 125/-; 1, 155/-.2 grinding wheels, switch and flex. Repair specialists.Lists free.-Easco, Electrical Service, 18 P.M., BrixtonRoad, S.W.9.

SURPLUS ELECTRICAL and EngineeringMaterials, low prices. -The London Electric Firm,Croydon.

12 -VOLT VOLTAGE REGULATORS, Explo-sion -proof, ex-R.A.F. ; ideal for Car or small LightingPlant; beautifully made ; coat pounds ; our price 4s.,post free. -LINCOLNSHIRE AIRCRAFT COMPANY,LTD., Hundleby Spllsby, Lines.

SUPER A.C. MOTORS. Brand new, h.p.,26/- ; h.p., 36/6 ; h.p., 60/-; larger sizes. ElectricTools, Machines, Pumps, Compressors, eto.--John P.Steel, Clyde Street Mills, Bingley.

ENGINEERINGMODEL parts machined. Boiler brazing, etc.

Estimates free.-LEWIS GATENBY, Engineer, 17Thornton Lodge Road, Huddersfield.

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BUILD and FLY your own AEROPLANEThe "SAFETY FIRST" Luton MINOR.Aero Engine .11prIte,' 25 h.p., 30-80 m.p.h. Set Blue -prints M.Pull set Materials, Wheels, Blue -prints, etc., 240. Semi -manufactured Set 275. Ready to flyaway. prices from 2180 to 2200.

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This coupon Is available until April 30th, 1987,and must be attached to all letters containing

queries.PRACTICAL MECHANICS, APRIL, 1937

ENGINEERING (continued)TURNING, welding, brazing done for Model

Makers. Neat, accurate work. Terms moderate.-ROBERTS, Engineer, Thornton House, LittleCoates Road, GRIMSBY.

ENGINES.WANTED. Petrol Engine. About 12 c.o. Complete

-Brooker, 15 Sterndale Road, W.14.

EXPERIMENTSTEN ELECTRIC EXPERIMENTS RARELY

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FOR SALETWIN TRAIN, controller, transformer, £1. Walker

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LITERATURECALVERTS MECHANICS YEAR BOOK 1937.

Over 190 pages. Illustrated Workshop Hints andCalculations. 8d. post free.-Endsor 416 Co., ProgressHouse, 75 Wood Street, Manchester, S.

WANTED, past " PRACTICAL MECHANICS."Exchange 110 latest " MODEL ENGINEERS " andexchange futures. -59 Langdale Road, Liverpool.

METALWORKMAKE METAL TOYS. Easy, profitable with

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MISCELLANEOUS" PHOTO -ENGRAVING." A practical hand-

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With compound slide -rest, El, or with hand-

reet only, 12 B.Screw Tall Stock 5/ -

extra. Post 1/-.THE SUPER ADEPT, 30 -.

F. W. PORTASS9

83a SellerSHEFFIELD.sStreet

WEBLEY AIR PISTOLSMarvellouslyaccurate fortarget practice.No license required to purchase.Senior 45/.., Mark I 30/-,Junior 20/-, Webley Air Rifle 84/.Write for List. WZBIAT & SCOTT LTD.,506 WZAMAN STRIST, &IMMORAL!, ENO.

BE TALLER (Inlhi'ess'Absierr)Increased my own height to 6 ft. 31 Ins.PM- ROSS SYSTEM NEVER FAILS 71

Full Details, 6d. stamp, or Complete System222n., mailed Privately In plain cover.P. M. ROSS, Heigla Specialist Scarborough,



BUY, EXCHANGE OR SELLMISCELLANEOUS (continued)

RAILWAY-CYCLE--ELECTRICAL. Send forfree list.-Kirby, 606-608 Washwood Heath, Birming-ham.

SHEFFIELD GUARANTEED SAFETY RAZORBLADES from 3s. 6d. gross (1.s. 10d. it gross, ls.

gross), post free.-Jas. Peat, Bradway, Sheffield.

BUILD YOUR OWN WORKSHOP, plans 2/-.-Robinson, 30 Queen Street, Doncaster.

MODELSEVERYTHING FOR electrical rewinds and re-

pairs. Screws, nuts, and washers for model engineers.Lists free.-Lumen Electric Co., Litherland, Liverpool,21.

MONEY -MAKINGOPPORTUNITIES

MONEY -MAKING OPPORTUNITIES con-stantly occurring ; highly recommended ; particularsfree. Send postage.-Messrs. Green, 17 Church Lane,Hull.

MOTORSMOTORS. Small practical power. Build

BUTLER'S 1/2 h.p. petrol motors. Most interesting-small power extent. Castings 9/9. Dynamo andmotor catalogue 3d.-Write BUTLER'S Profit-sharingWorks, Wade Street, Littleover, Derby.

MUSICAL INSTRUMENTSBAND GUIDE. Hints on the Bugle, Drum, Flute,

Staff Parade formation, etc. Free, post paid.-Potter's (Manufacturers), West Street, London, W.C.2.

PATENTSREGINALD W. BARKER & CO. (Established

1886), 56 Ludgate Hill, London, E.C.4.-Patent andTrade Mark Booklets Gratis.

PHOTOGRAPHY"PANTOGRAPHS " make large accurate drawings

from small photographs, printed drawings, etc.,easily. ls., post free.-Cooke, 83 Hawthorn Road,Levenshuhne, Manchester.

£500 worth good, cheap Photo Materials, Films,Plates, Cards, Papers, Chemicals, Catalogue

and 4 Samples Free.-Hackett's Works, July Road,Liverpool 6.

DON'T TAKE RISKS. Good developers meangood results. Our reliable stock developers keep twelvemonths after mixing. Satisfaction certain to amateursand professionals. Best developer ever put on themarket. Makes two pints strong developer. 6d. each,6 for 2/3, 12 for 4/-. Post free.-Hackett's Works,July Road, Liverpool 6.

PHOTOGRAPHY. Complete home photographyoutfit. Apparatus, chemicals, papers. etc. This out-fit enables the amateur to enjoy fully the photographichobby, to develop films and plates successfully and tomake beautiful prints on Gaslight or Bromide Papers.Complete instructions enclosed. Only 10/- post paid.Everything for amateur and professional photo-graphers. Interesting lists and samples free.-" KIM-BER'S," 105 Queen's Road, Brighton.

SITUATIONS VACANTG.P.O. ENGINEERING DEPT. (no experience

required). Commencing ES 13s. per week. Age18-23. Excellent prospects. Free details of EntranceExam. from B.I.E.T. (Dept. 579), 17-19 StratfordPlace, London, W.I.

1937 EDITION-FREE. AMBITIOUS ENGIN-EERS. Our new 268 -page Handbook shows clearlyhow to secure a recognised qualification, such asA.M.I.Mech.E., A.M.I.E.E., A.M.I.A.E., A.M.I.W.T.,A.M.I.R.E. We guarantee " NO PASS-NO FEE."Our book outlines over 150 Exams., and courses in allbranches of Civil, Mech., Elec., Motor, Radio, Tele-vision and Aero Engineering, Building, Governmentemployment, etc. In your own interests, we adviseyou to send for your copy of this enlightening Hand-book to -day - FREE and without obligation.-BRITISH INSTITUTE OF ENGINEERINGTECHNOLOGY, 140 Shakespeare House, 17-19Stratford Place, London, W.1.

25- E Din% if.

THE EYESTHEIR FUNCTIONCA4itiaRE:ILLS: CURE

the sou Wonderto D.., of

Mohan em .1. the Human Ban

A Pnceless Possesses

TO THE LOVERAND THE POET

THE EYEIS THE WINDOW OF THE SOUL'

but to most of us Good Eyesight is the first essen-tial for gaining a livelihood. Good Eyes in aman or woman command attention. Near sight,far sight, astigmatism and Tired Eyes are ahandicap in business and socia intercourse.ARE YOU BEING FAIR TO YOURSELF?Nature warns us of eyestrain by unmistakablesigns-a blurred vision, a headache, "spots"or a sense of Eye Weariness.DO NOT NEGLECT NATURE'S SIGNALSThere is generally no need for spectacles, opera-tions, or medicine. You can stimulate yoursight and Improve the Look of Your Eyes by asimple system of manipulation which you canpractise in your own home. This new scientific

p MASSAGE FOR THE EYEis a real Sight Saver and eApiainedin a Shilling Book which we areprepared to send FREE tosufferers from Eye -Defects, askingonly for 6d. (stamps) to coverpostage.

DELAYS ARE DANGEROUSSend NOW to

N EU-VITA (Dept. J.F.)163-252 Central Buildings, LondonBridge, London, S.E.1, England.

HOW TO OBTAIN

A PERFECT -LOOKING NOSEMY LATEST IMPROVED MODEL 25 cor-rects all111.shaped noses quickly, palnlesslY,permanently and comfortably at home. It is .

the only nose -shaping appliance of Preciseadjustment and a safe and guaranteed patentdevice that will actually give you a perfect.looking nose. Write for free booklet, testi-monials and money -back guarantee terms.

M. TRILETY, Specialist (D75),45, Hatton Garden, London, E.C.1.

MAKE MORE MONEY13 to 46 weekly can be earned at home in a wonderfulbusiness of your own. No matter where you live youcan commence to make money in your spare or wholetime. No risk, canvassing or experience required. Awonderful opportunity for anyone wishing to addpounds to their income. Particulars stamp.BALLARD, York House, 12 Hambrook Rd.,

LONDON, S.E.25

GRAMOPHONEATTACHMENTS for Radio, electric motors 25/-, Pick-ups 9/6, Portable Gramophones x2/-, spring motors4/6, dozen 36/-, I00 I2/Io, 1,000 Lloo, walnutpedestal Anexagram 5, Soundboxes, Tonearms,Horns, Cabinets, needles, gears, springs, accessoriescheapest. Quantity Buyers obtain lower prices.

Catalogues tree.REGENT FITTINGS COMPANY,

989D- 190, Old Street, London, E.C.1.

INVENTORS:VALUABLE GUIDE

General Advice Free. POST FREE 6d.

CHATWIN & CO. Est. 1880

Regd., Patent, Design and Trade Mark Agents foral I countries.

253 (D) Gray's Inn Road, London, W.C.1

Good Turners Command Good WagesTIPS FOR TURNERS

The Practical Handbook that TEACHES Turning and Screw.cutting. Twenty pages of useful tables. 28.64. (2d. postage).Manual Press (P.), 10 Crofton Rd., London, S.E.5

SITUATIONS VACANT (cont.)GET A BETTER JOB ! Learn book-keeping,

salesmanship, hotel book-keeping, journalism, etc., atlowest fees; prospectus free.-London School ofCommerce (Dept. P.M.2), 116 High Holborn, W.C.1.

VACANCIES for 1500 BOYSTHE ROYAL AIR FORCE requires 1,250 boys of goodeducation between 15 and 17 on 1st August for threeyears' training as Aircraft Apprentices in skilled trades.Good training, pay and prospects. Examinations atlocal centres throughout the country. Possession offirst school certificate, with passes in mathematics andscience, exempts from examination. Candidates notselected as apprentices may be enlisted as Boy Entrants,of whom about 300 are required. Apply for free Pam-phlet 15, to Inspector of Recruiting, Royal Air Force,Victory House, Kingsway, W.C.2.

WIRELESS & TELEVISIONMarconi's and other Employers require hundreds oftrained men.We train students for ALL BRANCHES OF RADIOat our Residential Colleges in Southampton andColwyn Bay, and GUARANTEE APPOINTMENTS.

LICENSED BY POSTMASTER GENERAL-RECOMMENDED BY MARCONI'S.

WRITE FOR FREE PROSPECTUS:

THE WIRELESS COLLEGE,COLWYN BAY.

Or to London Office, 4 WINTON AVENUE, N.11

STAMPSFREE ! Twenty Unused Colonials. " Neurope,"na.

Fifty for 9d.-G. H. Barnett. Limington, Somerset.

TOOLSGRAYSON'S Glass -boring Outfits and Tube.

Cutters avoid risk.-Below.

DRILLS, Taps, Dies, Files, Chisels and Punches.Best quality at keenest prices.-Grayson & Company,300 Campo Lane, Sheffield.

THE MYFORD 3 -in. LATHE. Have you seenour new superior model with additional refinements ?Standard model still in production. Economical infirst cost. Generous in design. Proclaimed best valueon the market. Write for illustrated list and instruc-tion booklet, or ask your local tool merchant.-MyfordEngineering Co., Neville Works, Beeston, Notts.

BRAND NEW, power tools of quality. 10" Band -saws, 50f- ; Jigsaws, 21/- ; Planing Machines, 80/- ; BenchDrills, 22/6 ; Sanders, 17/6 ; Circular Saws from 25/-;B.G.S.S.S.C. Toolroom Lathes £5 10s. Od. ElectricDrills, Grinders, Spray Plants, Guns, Air Compressors,etc.-JOHN P. STEEL, Clyde Street Mills, Bingley.

LATHES, drilling machines, chucks, workshop sup-plies, countershafts, A.C. motors. List 3d. off firstorder.-QUEEN'S ENGINEERING, 60 Queen's Road,

WANTEDWANTED, Lightweight model petrol engine, coil,

carburettor, tank. Reasonable price. No junkplease-PALLANZA, 42, Oseney Crescent, KentishTown, London.

WATCHMAKINGWATCH AND CLOCK REPAIRS. Everything

for the watch, clock and model maker. Large stockof watches, clocks, and clock movements, etc. Whole-sale prices. List 3d.-Blakiston & Co., Ainadale,Southport.

JOHN MORRIS, Clerkenwell Ltd., expert watchand clock makers, new parts and complicated work.Wheel and pinion cutting. Estimates free.-Below.

TOOLS and materials for the watch and clock -maker. Lathes Lorch, Woolf Jahn, Boley, etc., supplied.Set watchmaker's tools 5/-. Box material mixed 5/-.Stamp for list. -64 Clerkenwell Road, E.0.1.CLErk. 6077.

WATCH, CLOCK AND JEWELLERY REPAIRSa speciality. Materials, Tools, Inver Steel and Wheel -cutting. Catalogue 6d. Shockproof Watches from2/3. List lid. (Overseas excluded).-Young & Son,Material Dealers, Chippenham.


FIRST PARTS

NO ON SALE

rJ,1

31.1EFL.

TO BE COMPLE1EDASOUT 32 WEEKLY

PARTS,:

ict ')\ ri *F1 (PO.P1"

+.1S

PRODUCTION,ASSt ?ABLY. TESTING,

MAINTENANCEAND OVERHAUL

OF AIRCRAFT

e';.ito,6i'°,g,r,'Aue'r'''of:r.a,:etoyi,.

-- .

Surveip,txt.o: Araft,,toit,rc,

.,Gipsy 14.ior " Engine.,

Running & Maintenance

Data StneltShort " " Sint.P3'"

Mark tit Flying 8nat,

FREE DATA SHEET is given with everypart throughout this work.

ORDER FORMTo Newsagent.

Please supply each week one copyPart Work " AERO ENGINEERING,"

Name

of Newnes' Important NewI - weekly.

Address

" AERO ENGINEERING " is also obtainable direct from thePublishers, GEORGE NEWNES, LTD., Tower House, SouthamptonStreet, Strand, London, W.C.2 (I 2!.,d. each part, post free),

..)TO BE COMPLETEDIN ABOUT

32WEEKLY PARTS

)

TO -DAY there is a wonderful opportunity for men witha bent towards engineering.The Air Expansion Scheme has brought about a demand

for good men in the Aircraft Industry, and worth -whilepositions are vacant because these craftsmen cannot befound-yet. It is YOUR great chance. Aero Engineeringprovides to -day the opportunities which motor engineeringprovided years ago. You can benefit from these oppor-tunities if you acquire the necessary knowledge. This iswhere "AERO ENGINEERING," the Great New Part Work,will help you. It covers every sphere of Aero Engineering,and each shilling part is worth POUNDS to you !

Written by men with years of experience in the AircraftIndustry. Over 1,000 specially taken " action " photo-graphs and drawings, etc. Also many tables and data.

VERVIIBRIEF OUTLINE OF "AERO ENGINEERING."ESSENTIAL REQUIREMENTS OF MODERN AEROPLANES.PRINCIPLES OF FLIGHT. SURVEY OF MODERN AIRCRAFTPRODUCTION. WORKSHOP PROCESSES USED IN AIRCRAFTPRODUCTION. MACHINE TOOLS SHEET AND PLATE METALWORK. COMPONENT JIGS. AIR FRAME JIGS. MATERIALSUSED IN AIRCRAFT CONSTRUCTION. HEAT TREATMENT.THE ANODIC PROCESS. METAL CUTTING. WELDING,SOLDERING AND BRAZING. RIVETING. INSPECTION STAN-DARDS AND METHODS. AIR FRAME ASSEMBLY. ENGINE

INSTALLATION. FITTING THE ELECTRICAL EQUIPMENT.RIGGING. AEROPLANE MAINTENANCE. THE INSPEC-

TION SCHEDULE. GROUND EQUIPMENT, etc., etc.All the chief makes of AERO ENGINES and all rep-

resentative production types of Civil and MilitaryAircraft will be covered.

FILL UPTHIS FORM

TO -DAY!And hand to your Newsagent sothat you are certain to receive"Aero Engineering" each week.

George Newn cs, Ltd.

.111 applications respecting Advertising in this Publication should be addressed to the AD \ ERTISEMENT MANAGER, GEORGE NE \\ NES LTD.Tower House, Southampton Street, Strand, London, W.U.Y. Telephone: Temple liar 4353.

twww.americanradiohistory.com

"Give MeYour Measure and 1'11 Provein the First 7 Days

You Can Have a Body Like Mine!"No other Physical Instructorin the World has ever DAREDmake such an offer !

I'LL give you PROOF in 7 days that I ca,n turn you,too, into a man of might and muscle. Just think of it 1Right in the first week under my guidance you will

see and feel the improvement ! Then as my weeklyinstructions arrive in your home you continue tore -build, renew and " overhaul " your body. Bythe end of three months you are the owner ofa powerful body that you will be proud to displayanywhere, anytime I People willnotice the ruddy glow of healthin your face, the sparkle in yourclear eyes, your bread shoulders,and they will seek your company.You will be the fellow who willwalk off the prettiest girl and thebest job while the others wonderhow you did it.

FOREARM

141/2 IN.

I've No Use For /Apparatus

CHESTNATURAL

47 IN.I haven 't any need forapparatus

that may strain your heart andother vital organs. I don't "dose"or doctor you. DYNAMIC -TENSION is all I need.It's the natural, tested method for developing realmen inside and out. It distributes added poundsof powerful muscles over your body, gets rid ofsurplus fat, and gives you the vitality, strengthand pep that win you the admiration of everywoman and the respect of any man.

Are you underweight ? I'll add pounds wherethey are needed ! Are you fat in spots ? I'll showyou how to pare down to fighting trim. Andwith the big muscles and powerful evenly developedbody that my method so quickly gives you, I'llalso give you through -and -through health-that digs down into your system and banishes suchthings as constipation, pimples, bad breath andthe hundred -and -one similar conditions that rob youof the good times and the good things of life.aaaCHARLES ATLAS Toil.40, Chandos Street, London,W.C.2I want the proof that your system of DYNAMICTENSION will make a New Man of me-give me ahealthy, husky body and big muscle develop-ment. Send me your book, " Everlasting Healthand Strength," FREE.

NAME

(Please print or write plainly)

ADDRESS.U

NECK

17 IN.1

THIGH

231/4 IN.CALF

16 IN.

HEIGHT

5 FT. 10 IN.WEIGHT

13 STONE.

AIST

32 IN.

This is the latest photo ofCHARLES ATLAS, holder ofthe title " The World's MostPerfectly Developed Man,"showing how -she looks to -day.This is not a studio picture butan actual untouched snapshot.

48 -PageFREEBook

It tells you all about myspecial DYNAMIC TENSIONmethod, and what it has done

to make big.muscled men out of run-downspecimens. It shows you from actual photoshow I have developed my pupils to the samePerfectly balanced proportions of my ownphysique. What my system did for me andthese hundreds of others it can do for youtoo. Don't keep on being only half of theMan you CAN be ! Find out what I cando for you. Where shall I send your copyof " Everlasting Health and Strength "Put your nameand address on .the coupon,and post itto -day.CHARLESATLAS,Dept. io-R,40, ChandosSt., London,W.C.2.

AMAZING RESULTS IN ONE WEEK"Here are the increases at the end of ONE week : Arm relaxed li in more, forearmin., chest, normal, 3 in.. weight 5 pounds gained. I feel healthier, stronger and

more vital. I did not think that any course could do for me in a month what yourcourse has done in only one week, and when I go out for a walk with my chest out andshoulders back, my trends lock at me with admiration. I owe it all to you."-L. R. V.

Published shout the attli of each month by GEORGE NEWNES, LIMITED., Tower House, Southampton Street, Strand, London, W.C.2, and Printed in England byHAY.1.11, WATSON & LTP., London and Aylesbury. Sole Agents [or Australia and New Zealand-Gordon & Gotch Ltd. Sole Agents for South Africa-Central New,.

Agenc3 Ltd Subscription Rates: Inland and Abroad. Ia. Ed. per annum : per annum. Registered at the G.P.O. for transmission by Canadian Magazine Post.

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