Franklin as a man of science and an inventor

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  • JOURNALOF THE

    FRANKLIN INST TUTF OF T H E STATE OF PENNSYLVANIA

    FOR T H E P R O M O T I O N O F THE MECHANIC A R T S

    VOL. CLXI, No. 5 8IST YEAR MAY, 19o6

    T h e Franklin Inst i tute i s not respons ib le for t h e statementsand opin ions advanced by contributors to t h e Journal

    T H E F R A N K L I N I N S T I T U T E .

    Franklin as a M a n of Science and an Inventor.*[An address delivered by Dr. E d w i n J. Houston, Emeri tus Professor of

    Physics, Frankl in Institute, o n February 21, 19o6, on the occasion of the 2oothanniversary of the b i r th of Benjamin Franklin.]

    (Concluded from voL clxL 2" 3 I6)

    "Fig. ii is to represent the elevation of a water-spout, wherein, I sup-pose P P P to be the cone, at f irs t a vacuum, till W W, the r is ing coiumnof water , has filled so much of it. S S S S, the spiral whirl of air sur-rounding the vacuum, and continued higher in a close column after thevacuum ends in the point P, till i t reaches the cool region of the air. B B,the bush described by Stuart, surrounding the foot of the column of water.

    (h) "Now, I suppose this whirl of air will,at first, be as invisible as the airitself, though reaching, in reality, from the water, to the region of cold air,in which our low summer thunder-clouds commonly float; but presently, itwill become visible at its extremities. A t its lower end, by the agitation ofthe water under the whir l ing part of the circle, between P and S, forming Stu-ar t ' s bush, and by the swelling and r is ing of the water , in the beginning vacu-

    *Copyrighted by Edwin J. Houston, 19o6. 'VoL. CLXI, No. 965 2 1

  • 3 2 2 2r-Zoltstolz ." [J. F. I.,

    S m ~

    B

    Fig. 11. E levat ion of W a t e r Spout .(Franklin)

    urn, which is, at first, a small, low, broad cone,whose top gradually rises and sharpens, asthe force of the whirl increases. At itsupper end it becomes visible, by the warmair brought up to the cooler region, whereits mois ture begins to be condensed intothick vapour, by the cold, and is seenfirst at A, the highest part, which beingnow cooled, condenses what rises next atB, which condenses that at C, and thatcondenses what is r is ing at D, the cold op-e ra t i ng by the contact of the vapors fasterin a r igh t line downwards, than the va-pours themselves can climb in a spiral lineupwards; they climb, however, and as bycontinual addition they grow denser , and,concentrating currents that compose thewhirl , they fly off, spread, and form a cloud.

    "It seems easy to conceive, how, ~oythis successive condensation from above,the spout appears t o drop o r descend fromthe cloud, though the materials of which itis composed are all the while ascending.

    "The condensation of the moisturecontained in so great a quant i ty of warmair as may be supposed to rise in a shor ttime in this prodigiously rapid whirl, is,perhaps, sufficient to form a great extentof cloud, though the spout should be overland, as those at Hatiield; and if the landhappens not to be very dusty, perhaps thelower par t of the spout will scarce becomevisible at all; though the upper, o r what iscommonly called, the descending part, bevery distinctly seen.

    "The same may happen at sea, in casethe whirl is not violent enough to makea high vacuum, and raise the column, &c.In such case, the upper part A B C D onlywill be visible, and the bush, perhaps,below.

    "But if the whirl be strong, and therebe much dust on the land, and the col-

  • May, 19o6.] Frauklin as aMalz of Scienec and an I~wentor. 323

    unto W W be raised from the water, then the lower part becomesvisible, and sometimes even united to the upper part. For the dust may becarried up in the spiral whirl, till it reach the region where the vapour iscondensed, and rise with that even to the clouds: And the friction of thewhirling air, on the sides of the column W W, may detach great quantitiesof its water, break it into drops, and carry them up in the spirial whirlmixed with the air; the heavier drops may, indeed, fly off, and fall, in ashower, round the spout; but much of it will ,be broken into vapour, yetvisible; and thus, in both cases, by dust at land, and, by water at sea, thewhole tube may be darkened and rendered visible.

    "As the whirl weakens, the tube may (in appearance) separate in themiddle; the column of water subsiding, and the superior condensed partdrawing up the cloud. Yet still the tube, or whirl of air, may remain en-tire, the middle only becoming invisible, as not containing visible matter."

    (a) Here we have the ring of the true philosopher: "Nothing,certainly, can be more improving to a searcher into nature thanobjections, judiciously made, to his opinion, t a k e n up, perhaps ,too hastily." Franklin welcomes the fair criticisms of theBoston Doctor.

    (b) " I am so engaged in business, public and private." To allwho are acquainted with the immense amount of work perform-ed by Franklin, it is no t surprising that he finds but compara-tively little time for the more pleasing investigations of science,But it was then , as it is now, that it is the busiest man who finds-.time for all necessary w o r k , and F r a n k l i n certainly found time.in this case to prepare the most excellent scientific paper he-sent to the Boston Doctor.

    (c) Even if the vacuum were complete, the height of the col-umn that is pressed inwards by the weight of the atmosphere~could not. greatly exceed thirty feet . ~:

    (d) " I must , however, no longer call it my hypothesis ." Agenerous statement , s ince Stuart 's explanation was certainlyvery obscure.

    (e) F r a n k l i n is quite correct in this supposition. Thewhirlwindand the waterspout are the same phenomena, being due to thesame causes, with, however, the difference that the whirlwind isproduced by a whirling c o l u m n of air pass ing over the land,while the waterspout is produced by this c o l u m n pass ing overthe water. Note here the clear and logical statement as totheir resemblances.

  • 324 Z-tous lon : [J. F. I.,

    (I) Both waterspouts and whirlwinds possess a progressiveas well as a ro ta ry or circular motion.

    (2) Both waterspouts and whirlwinds occur after periods ofgreat atmospheric heat, when the air has been free from winds.

    (3) The wind blows in all directions from the extended spacesurrounding both water-spouts and whirlwinds directly towardsthe water-spout or the whirlwind.

    (4) When waterspouts, by reason of the i r progressive mo-tion, leave the sea and move over the land, they produce all thecharacteristic effects of whirlwinds, thus showing them to bethe same.

    (5) /3cth waterspouts and whirlwinds occur most com-monly during the day time.

    (f) Franklin now proceeds to apply his theory as regards theformation of waterspouts, producing for this purpose a plan andan elevation of the spout as he conceives it to be produced. HeLases his theory on two assumptions, that all should be willingto admi t ; i . e . , - -

    (i) A higher temperature in the lower regions of the atmos-phere than in the upper regions, and, consequently, a morerarefied condition near the surface of the earth than in the up-per regions. Such a condition would, of course, necessitate anabsence of wind.

    (2) An exceedingly moist condition of the atmosphere.Franklin then draws a picture of an extended area of land or

    sea, of, as he says, perhaps sixty miles square. Ur~der condi-tions of prolonged calm, and with no clouds in the sky to pre-vent the sun's heat from freely reaching the earth's surface,these conditions perhaps continuing for several days, the lowerstrata of air become intensely heated. He then pictures thesurrounding air as being relatively much colder, and as, there-fore, remaining much heavier than that over the heated area.Under these circumstances, there would necessarily be produc-ed a rising or ascending current of the lower air, accompaniedby the descent of the colder and heavier air. But this risingdoes not immediately take place alike over all portions of theheated area. It begins over that portion of the area which is

  • May, 19o6.] Franklin as aMan of Scienec and an Inventor. 325

    the m o s t h i g h l y h e a t e d , the r e m a i n i n g p o r t i o n of the w a r m airf l o w i n g horizontally over all por t ions of the h e a t e d a r e at o w a r d s this c o l u m n . In this w a y , the w h i r l is f o r m e d p r e t t ym u c h as F r a n k l i n r e m a r k s , like the funnel-shaped d e p r e s s i o np r o d u c e d in the s u r f a c e of the w a t e r in a tub, that is d i s c h a r g i n gi t s w a t e r t h r o u g h a hole or o p e n i n g in the b o t t o m of the tub.

    F r a n k l i n then p o i n t s ou t the fact that s i n c e i n f l o w i n g h o r i -z o n t a l c u r r e n t s p o s s e s s c o n s i d e r a b l e m o t i o n , w h e n they r e a c hthe c e n t r a l r i s i n g c o l u m n , they are u n a b l e t o s u d d e n l y c h a n g et h e i r d i r e c t i o n t o that of the vertical m o t i o n , so that they jointhe a s c e n d i n g c o l u m n by m e a n s of a s p i r a l m o t i o n .

    F r a n k l i n then p o i n t s ou t the fact that the veloci ty of theinflowing c u r r e n t will necessarily be g r e a t e s t in t h o s e por t ionsw h e r e the t e m p e r a t u r e of the air is g r e a t e s t ; i. e., n e a r t h ehighly-heated s u r f a c e . C o n s e q u e n t l y , it is here that the w h i r l -in~ m o t i o n is the swiftest, a n d , therefore, the v a c u u m m u s t beg r e a t e s t near the e a r t h ' s s u r f a c e , d e c r e a s i n g as the c o l u m nr i s e s .

    (g) F ig . IO is clear, and n e e d s no explanation. The r i s i n g ofthe w a t e r from the s u r f a c e of the sea is a n a t u r a l r e s u l t of thep a s s a g e of the v a c u o u s a r e a .

    (h) T h e w h i r l i n g m o t i o n of the air is at f i r s t invisible, butf o r m s a m a s s of c l o u d s as soon as the m o i s t air is c o n d e n s e d bythe c o l d . It is for this r e a s o n that the s p o u t may s e e m t o dropor d e s c e n d from the c l o u d s , a l t h o u g h the m o i s t u r e of w h i c h it isf o r m e d has been continually a s c e n d i n g .

    I n a d d i t i o n t o the v a l u a b l e p a p e r s p r e p a r e d by F r a n k l i n ong e o g r a p h i c a l p h y s i c s , t o w h i c h we have a l r e a d y r e f e r r e d ; i. e.,the p a p e r as t o the c a u s e of t h u n d e r - s t o r m s , the a u r o r a b o r e a l i sand w a t e r s p o u t s , t h e r e yet r e m a i n s t o be d i s c u s s e d an o b s e r -v a t i o n of very g r e a t v a l u e r e s p e c t i n g the c a u s e of the g r e a tn o r t h e a s t s t o r m s of the U n i t e d S t a t e s . S i n c e , as is now wellk n o w n , the g r e a t e r part of the w o r k of the U n i t e d S t a t e sW e a t h e r B u r e a u as r e g a r d s the p r e p a r a t i o n of forecasts ofc o m i n g c h a n g e s in the w e a t h e r , is b a s e d on the peculiarities ofthe m o v e m e n t s of o u r g r e a t n o r t h e a s t s t o r m s , it will r e a d i l y beseen that this d i s c o v e r y of F r a n k l i n ' s s h o u l d be r a n k e d a m o n gthe m o s t i m p o r t a n t of his r e s e a r c h e s in g e o g r a p h i c a l p h y s i c s .W h i l e from a p o p u l a r standpoint , this m a t t e r is not so a t t r ac t -

  • 326 ]-]ouston : [J. F. I.,

    ive as his d e m o n s t r a t i o n of the ident i ty of d i s r u p t i v e electricd i s c h a r g e s a n d l i g h t n i n g , yet from a scientific standpoint , its h o u l d c o n t r i b u t e t o his m e r i t e d r e p u t a t i o n as a philosopher,as m u c h , if n o t m o r e , that his f a m o u s k i t e experiment . T h e n ,too , from a p r a c t i c a l s tandpoint , w h i l e it m i g h t s e e m that theinvention of the l i g h t n i n g rod was o.f m o r e d i r e c t b e n e f i t tom a n k i n d , yet the s a v i n g of life and p r o p e r t y that w o u l d fre-q u e n t l y r e s u l t from the t i m e l y w a r n i n g of the a p p r o a c h of ad a n g e r o u s n o r t h e a s t s t o r m w o u l d p r o b a b l y be i m m e n s e l yg r e a t e r than w o u l d ever be p o s s i b l e by p r o t e c t i o n a f f o r d e d byl i g h t n i n g r o d s .

    F r a n k l i n i n f o r m s us j u s t how h e c a m e t o t h i n k of the c a u s e sof the g r e a t n o r t h e a s t s t o r m s in this c o u n t r y as s t a r t i n g in ana r e a of low b a r o m e t e r s o m e w h e r e in the wes t and p r o g r e s s i n gg e n e r a l l y t o w a r d s the nor theas t . I t a p p e a r s that a n e c l i p s e ofthe m o o n was t o be v i s i b l e at P h i l a d e l p h i a o n a c e r t a i n F r i d a yat 9 P . M . F r a n k l i n made p r e p a r a t i o n for the p r o p e r o b s e r v -ing of this eclipse, but, unfortunately, that n i g h t a s t o r m visitedPhiladelphia, a p p r o a c h i n g the c i ty from the nor theas t , a n d con-t i n u i n g violently all that n i g h t and the n e x t day, p r e v e n t e d anyo b s e r v a t i o n s of the e c l i p s e from b e i n g m a d e . T o F r a n k l i n ' sg r e a t astonishment, the n e w s p a p e r s c o n t a i n e d a n a c c o u n t ofthe fact that this eclipse h a d b e e n o b s e r v e d in the c i ty of B o s -ton . S i n c e this s t o r m a p p a r e n t l y a p p r o a c h e d the c i ty of P h i l a -d e l p h i a from the nor theas t , it w o u l d s e e m that it s h o u l d haver e a c h e d B o s t o n b e f o r e it r e a c h e d Philadelphia, B o s t o n b e i n g ,as is well k n o w n , n o r t h e a s t of the c i ty of Philadelphia. W r i t -ing t o his b r o t h e r , w h o l i v e d in the c i ty of B o s t o n , he a s c e r -t a i n e d the fact that the e c l i p s e was over a t l e a s t o n e h o u r b e f o r ethe s t o r m c o m m e n c e d . This c a u s e d F r a n k l i n t o m a k e f u r t h e ri n q u i r i e s , w h e n h e f o u n d t h a t , as a r u l e , the g r e a t n o r t h e a s ts t o r m s of this c o u n t r y b e g i n t o the l e e w a r d ; i. e.., s t a r t s o m e -w h e r e t o the s o u t h w e s t , then m o v i n g in a g e n e r a l n o r t h e a s tp a t h a c r o s s the c o u n t r y .

    In a l e t t e r t o the Rev. J a r e d El io t , d a t e d Philadelphia, JulyI6, I747, F r a n k l i n s a y s :

    "We have freqently, along this Nor th American coast, storms from thenortheast, which blow violently sometimes three or four days. Of these Ihave had a very singular opinion some years, viz., that, though the course

  • May, 19o6.] Franklin as aMan of Scienec and an Inventor. 3 2 7

    of the wind is from northeast to southwest, yet the course of the s t o r m isfrom southwest to northeast; t h a t is, the air is in violent m o t i o n in Vir-ginia before it moves in Connecticut, and in Connecticut before it moves atCape Sable, &c. My reasons for this opinion, (if the like have not occurredto you,) I will give in my next."

    I n a n o t h e r l e t t e r t o t h e s a m e g e n t l...

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