2d

MEASUREMENT OF COSMIC RAYS AT AGRA AND KODAIKANAL

By

A . K. D A S

A M )

M. S A L A R U D L I N

fin InihlicalioUf A 11 il S'., ifjjo)

Plates VIII tv' IX

ABSTRACT. Co.smu-rav iiileii.sitics li;ive been measured at Agra anil Kodaikaiial l>y iiifuns of a Kolhorstcr appar.ntus with a shield of iron ,s"‘5 thick. The intensities liave been reduced to standard pres,s u i t s , for Agra and Kodaikanal .separately, by means of the regri'ssion eocflieient.s calculated from the intensity and pressure data. The mean intensity values obtained after correcting for barometer eficct are for Agra i ’,S'l5±o’oo7 and for Kodaikanal 2‘333 + o’oio pairs of ions cm.“* .sec."'

I'rom these values, after allowing for latitude effect the ab-sorptioii eocilieient'of co.smic rays has been calculated. 'I'he absorption coefficient obtained, v i r . . , o'zoa per metre of water agrees well with the values obtained bj' JlilHkan and Cameron.

lly means of this coefficient of absorption the absolute intensities of cosmic rays without shield have been deduced. These values of 2’oo7 and 1925 pair.s of ions pci- cni'i sec' for Kodaikanal and Agra respectively compare well with Compton's intensity values for the .same latitude.s. The intensity data for Agra and Kodaikanal arc then analj'.sed according to mean and sidereal times. The curves for the mean .solar lime for the two .stations agree with cacli other and with the corresponding curves of other investigators but no siniil.irity has been found between the sidereal time curves of the two stations.

Mean daily co.smic-ray intensities have been I'orrelaled with .solar acti\ily represented by sunspot numbers and lloccnli figures but no relationship has been hmnd to exist between them.

In recent tinie.s the geographical distribntioii of co.sniic-ray intensities has

formed one of the important aspects of the .study of cosmic radiatiott. Tlie world surveys of cosmic radiation organized by A. H. Compton and I)y R. A.

Millikan have shown the utility of such studies particularly with regard to the discovery of the nature of the jtarticlcs which constitute this radiation. In spile of these expensive surveys it has not been possible, we believe, to collect data from as many representative countries as would have been desirable and it is likely to be helpful for a general study to secure observational data from such latitudes

as do not seem to have been well represented in the w-otld surveys. India .seems to be one of the countries from which very little data on cosmic ray intensity are

192 'A, K. Das andWl. SalarmlcUn

uvaikiblu, rufcrcnccs that wc have been al)lc to find about this typeof weak in India are the nieasmeinents by J. M- Bcnade in Aunnst, 193::, at Lahore mnlei the scheme of co-ordination initialed by Compton and the bailoon ol.servations made at Madras in (October, U)3b, by JL V. Nehcr a e(dia))oratn] of Millikan. Tile measurements considered in the present paper, tlioueh not numerous, have tlieiefore ajipeared to us to be worth publisli- injLi,. II i'-, how ever, intendetl that tile measm emeiits should be eontinued fora lew yuus in older to ol»lain a sulTiciently lotij.; series ol data capable ul vieldiny deiiiiilive values of the intensity of C(vsniic radiation in India.

n: X p I-. K I :\i n: n ' i ‘ a p a k k a n ( . e; jAI i - n t s

'D e iiieasiiieiiieiits dij-eitssed in this j)aper weie n ade at A»era (Lai.l^one. 7^'"i') and at Kodaikanal (Lai. 10 ' i,|' Lonj. / / iS'). Altlioni li theelioiee of these two stations was dictated by reasons other than the requirements of this investi.L;atimi, these stations liappeu to reiircsent ty|)ical localities well suited f(Ji this kind of work, i'hey differ ai)preciably in latitude and consider- aljly in altitude, Agra lieiiig praclically a seadew'el station about 55 feet above mean sea level and Kodaikanal a hill station about 7700 feet above mean sea level, 'riie apj>aratus used ftn these observations was a Kolhdrstcr electroscope of the latest tyjie belonging to the India IMeteorologieal Departmeift. It had pioved to i)e perfectly satisfactory for the measinemeiits of cosmic radiation made by one of us (A K.D.) during two sea x'oyages between India and Hnropc and at Cainbi idge. ’ As it has frequently l)eeii contended by workers on cosmic lays that intensity measurements aie alTectcd ])y instrumental bias, it seems desirable to give a brief description of our ap])aratus although the jirinciple of this instrument is woll knowm from Kollibrster’s dcvScriptions. The complete apparatus shown hi Plate VIII coiis.sts of a cylindrical ionisation chamber * A ' made ol sheet iron . >'5 iiiin tlnck and fitted witli a bia.ss lid of 3’5 mm, thickness, 'i'he clmmber is sealed air-tight and filled with air (at nearly atmospheric pressuiv specially dried and freed from radio-active substances. The air*tightness of the ionisation chamber can be checked by means of a thermometer T ’ and a [iiecision aneroid barometer ‘ P ' attached to the instrument. The electro- ineler is sealed inside the ionisation chamber and its deflections can be read with the help ol a niicroscoiie lilted to the lid. It consists of a pair of exactly similar loops of (luarlz fibre mounted on a frame w’ith a iiickel-steel-quartz temperature comiiensation, the frameVung fixed upon the objective of the view­ing microscope. 'Hie elci'trometcr being well insulated from the walls of the ionisation cham1)er, the loss of charge through leakage is extremely small. Through the microscope the quartz loofis can be .seen only edgewi.se so that they appear as two straight dark filaments against the microscope scale divisions. The filaments and the scale divisions are illuminated by means of a small

ALARUDDIN* LM I HD Vlll lA.

PLATE VIII PLA IT IX

clciic.tiic lciiii|) iittccl inside li iiictcil tuL)c j\I tiiul screwed on to tlic window «il the back of the ionisation cliamher. 'riic instrument can be used for visually reading the deflections of the electroscope ; it is, liowewr, provided with a camera 'C '(w ith a rotating drum for i)holographic paper) which can be fixed on the eye i>iecc cud of llic microscope for obtaining a continuous j^hotogra- phic record of the separation of the electroscope lilameiits. For the present oKser- vations, the latter method was exclusively employed.

1 he walls of the ionisation chambei' are thick enough to prc\'cnt any ot or rays from entering it ; Imt in order to eliminate the possible elTect of even the

most peiietiating y rays of knrjwn radio-active origin, the apparatus was etielosed ill an iioii shield ol 5 5 inches thickness all round J'he shield was built nj> as a rectangular box from several iron plates for I'onvenience of manipulation'. Iu>i charging the eiccti'omeler at inteix'als, it was iieeessarv to make one w’all of the shield easily removable and consequently it was found essential to keep down its xveiglit as much as possible. Accordingly, the sliield w’as made just large enough to enclose the ionisation chamber only, so that the end of the microscope tube carrying the camera projected out of the shield through a hole in the movable xvall. The movable wall itself had to be made of tw o halves mounted in such a w ay that they could be slid along iron gn^oves with ball runners. This arrangement necessaril} involved a certain amount of leakage of y rays into the ionisation chamber, imt we do not think that it could have been large enough to affect materially the measurements of the cosmic rays.

The experimental material utilised in this work consists of complete records for 23 days in June-July, 1036, at Agra and for 13 days in February, 1038, at Kodaikanal. At Agra the whole apparatus was installed in a canvas tent well away from buildings and at Kodaikanal the apparatus was housed in a wooden hut previously used for housing magnetic instniments. The clccironieter w as charged each time to about 300 volts and was allowed to discharge itself till the voltage dropped to joo volts. Below 100 volts the ionisation current no longer corresponded to saturation, so that tlie electrometer had to be charged up again. This necessitated charging the electrometer twice a day at Agra and three limes daily at Kodaikanal where the loss of charge through ionisation was faster. Charging of the electrometer was done with the help of a magnetic probe and a charging terminal fixed on the lid of the ionisation chamber but insulated from it by means of an amber insulator, ‘he battery used for charging was a Zamboni pile the positive pole of which was connected to the charging termmaJ of the electrometer, the other pole being earthed. The probe which is inside the ionisation chamber was then brought into contact with the inner end of the charging terminal by turning it over with the help of a horsc-s'iioe magnet attached to the outside of the lid. The charging now finished, the probe was again turned back to its initial position so as to keep the electrometer disconnect-

Measurement of Cosmic Rays at Agra and Kodaikanal 193

194 A. /\. Das and M, Salaruddin

ccHrom llie rliari iiiK tcniiinai. The separation of the clcclroiiieter filaments when eharged could be observed through a window in the camera by means of a reflex arrangement. The time of the opening or the closing of the shutter was noted whenever this was done for charging the electrometer or for changing the photographic paper, A sample record obtained from the instrument is shown in Plate IX. This is a C(.)py of the Kodaikanal record of I'ebruary 17-iS, 1938 on a reduced scale. There are three i)airs of electrometer traces on the chart. Kach pair begins with full charge when there is the greatest sc]>eration between flic filament traces and then gradually the traces come nearer together as the charge decreases. 'J'hc very line and close lines running along the sheet are the traces of the microsco]>e SiMle divisions, d'hc rather thick lines across the sheet are the hour marks which are registered by means of a device in the clock work which short-circuits the lani]) once every hour. The sheets weie measured by means of a low-power travelling microscope, 'flic procedure was to count the number of scale divisions between the electrometer traces at every hour mark and at every point corresponding to the time of the opening and closing of the exposing shutter. The limes corresponding to tlie hour marks were deduced from the times of the opening and closing of the shutter after making due allowances for the rate of tlic clock. The linear distances l)etvvceii the electro­meter traces, /.t'., the number of scale divisions counted, were then converted to volts by means of a calibration curve prepared by one of us (A.K.D.) with tlie help of a fine precision potentiometer at the ]\Iectrical luigineering laboratory of the Ijnivcrsity of Cambridge.

vSince all other sources of ionisation have been eliminated by the nse of the iron sliieldj the loss of charge of the electrometer must be due to cosmic rays alone. Accordingly the rale of ion formation is a measure of the intensity of the cosmic radiation. In order to obtain the rate oi ionisation, all the readings of the electrometer in volts were tabiilaied against the corresponding times so that the values of volt difference (dv) and of time dilTcrcucc (dT) were directly obtained from the tables. The rate of ionisation, /.c., the number of ion-pairs per cm.' per second, was then calculated according to the usual formula for this kind of instruiiieiit.

, _ C dv300 X 60 X c X L dT ■ dT

where j = iiuinber of iou-pairs/cm.’’ /see., C=ca])acity of the electrometer

= o‘2b8 cm.I.=iiitcrual volume of the ioiiisatiou chamber reduced to o"'C and 75o mm.

pressure = 3801’06 cm.’’ , c = electronic charge = 4'78 x lo " ’ " c.s.u. and =

decrease of voltage per minute.

The residual ionisation of the apparatus as determined and given by the makers, Gunther and Tegetmeycr of Braunschweig, is ion-pairs per cm.*])Cr second. By subtracting this value of the residual ionisation fioni the total ionisation represented by J, the ionisation due to external causes or the intensity of cosmic rays * I ’ was obtained.

]\ A O J\T JC T K R 1 V V K C T

The intensity of cosmic radiation measured at the surface of the earth must 1)C expected to be influenced l)y meteorological conditions and conseejuentiy it is essential to reduce all observations made at different times to standard meteorologi­cal conditions in order tliat lliev may be comparable. The atmospheric factor which affects cosmic-ray intensity most is the barometiic t>ressure, llie effect of temperature, humidity and other elements being comparatively small. This fact observed by most investigators, was ]>rought out very clearly by the metliod of multiple correlation used by A. Coriin uho obtained the following correlation coefficients for inessure (RIB) temi)eratnre (\\VV) and humidity (Kill) foi the three periods for which he analysed his data.

Measurement o/ Cosmic Rays at Agra and Kodaikonal 195

P c i incl1

I 1i

11 111

RTU — 0-58^ r 0-0 0 — + 0‘03/|

RIT — 0-1 57 1 ■1 n -t n*n6S

R in ■ l-n-luS C'O/i s — 0- i3.S + "'0 17 1 o-0]fi + o-(jhS

It is clear from the abow- table that only incssure has a real influence' on the intensity of cosmic rays, the otlier factors having a very small and uncertain influence. We have' therefore applie d only coric'ction for the pressure effect in the

present work.The barometer effect was deduced by arranging the intensities according to

different values of pressure, working out their means and then applying the method of regression coefficients, ff'he pressures at the mean times of observation were obtained from the charts of self-recording microbarographs of the Agra and Kodaikanal observatories. During the periods of observation here considered the barometric laessure varied l)elwccn 28-85" and 29*09'' at Agra and between 22'69" and 22*90'' at Kodaikanal. In order to reduce the intensity values for each station to some standard pressure, the following procedure was adopted. All the intensity vaJuCvS were tabulated separately for Agra and Kodaikanal according to different values,of pressure at intervals of o-oi". The mean values of intensity ‘ I ’ for different values of pressure P were deduced and the regression coeflScients

196 A . K . Das and M. Salaruddin

R between these values \\ ere thcu calculated from the following fornmlji

R= ^ U ( P - P)}s . u p - f F }

where /> is the mean of all P values.The rc uression coelhcieiils derived from A^ra and Kodaikanal data are

*-u*o7S ] and —0 040 I ])er inch of mercury respectively. With these coefficients the values of I for Agra and Kodaikanal were reduced to the standard pressures of 2c/o" and 22 S'' respectively. We denote these intensity values reduced to standard i>ressure by Jo-

A n S o R P T I () N 0 U K 1' T C I IC N T O V C O S 1 C K A V vS

The mean value of the intensity of cosmic rays at any place dej)eiids i)rimarily upon the allilude and the latitude of the station. If for the mean values of lo obtained for Agra and Kodaikanal allowance is made for the eflect of latitude, then the remaining dilTereiicc' between the intensity values would be mostly due to the elTect of altitude and from this the absorption coefficient of cosmic rays can be calculated, 'khe fact that c(»smic-ray intensity varies with the geomagnetic latitude^ is now well established. The results olAained by Clay, Compton, Hoerlin, Nelier and others show that cosmic-ray intensity is nearly constant from about latitude 30'’ to the pole both :u the northern and southern hemisi>here , but decreases steadily towaids the equator, the decrease amounting to about 14 per cent, at sea level and much higher at higher altitudes. The geographical latitudes of Agra and Koilaikaual are .7' N and to‘’ 14' N and their geomagnetic latitudes aie 17'' 21' iV and o 3 7 'N resi)ectively. 'I'he gefimagiietic latitudes were caleulated frtmi the formula

sin A “ sin cos 0 cos </> + cos sin

where A is the geomagnetic latitude, the colatitude ol the north pole of uniform magnetisation, 0 the geographical latitude of the place and ' 8' is the westlongitude of the place.

From Compton’s ' inleiisity geomagnetic latitude curve for sea level (which includes the data of Clay, Millikan and others), the percentage decrease in intensity from latitude 1 7 ” to the equator is about t and the same from the curve for 2000 metres (about 6hoo ft.) altitude is 2-5. The altitude of Agra and Kodaikanal being 554 feet and 76SS feet respectively, the intensity at Kodaikanal has to be increased by 2 per cent, lo reduce U to Agra latitude. Then this corrected intensity can be compared wUh the intensity at Agra and the altitude effect can be deduced.

Uv geomajiimAii’ lalitiuk is meant the latitude redative to the pole of uniform magiielisalion of the eartlv which is at 78“ 32' N and 69” 8' W and is diflcn'iit from the magnetic latitude which is defined bv Ujc formula tan tan 5, where ft is the magnetic latitude and 5 is the dip of the magnetic needle.

The mean cosmic-ray intensities meusurccl at A«ra and at Kodaikanal arc r5 ')5± ’007 and ion-pairs cni.~ ''sec.' ' respectively. The intensity atKodaikanal reduced to Agra latitude would then be ion pairs cm. sec ' We can take it that the intensity o£ e . So ion-paiis cni. ''‘ sec.“ ' becomes ieduced to 1-54.S ion-pairs cm.~'* .sec.“ ' through absorption by an air column of de]»th corresponding to 6-e" of mercury, this being the diiference between the mean barometric pressures of Agra and Kodaikanal. Assuming that the cosmic rays are absorbed exponentially, their absorption coefheient can then be calculated by ijicans of the simple formula

[Measurement oj Cosmic Rays at Agra and Kodaikaiml 197

T , -/U/ I - OoR 1,),

where M is llie absorption t'oerricik‘iit, and lo are the intensities of rays when tliey enter aiul when they leaw* thu absurbinsj: layer resjK’etively, and d is tlie depth of the layer. Using ay)])ropna1e values for Agra and Kodaikanaliii tlie above formula we obtain

u)()(va X T -h X

(In.- W'xi-log I’SI 5)

- - o ‘ o o : i ( I , ! t ' l n . " " g m . ' '

— pel metre of water.This value of absorption coerricient agiees with the values olitaiiied l)y ^Millikan and Cameron '* in their exi>erimenls in the higli nllitnde lakes of America.

A u vS o I, V r iv T N 'j N I 'I' 1 n s o I' r o s m i c k a y s

'I'he mean eosmie-ray intensity values of and r5.]5 ion-pairs/eni.’ hsce.obtained at Kodaikanal and Agra res[)ectively arc those measured inside an iron shield of 5-5 inches thickness. The absolute intensities lu and 1 , (/.c., the intensities without tlic shield) can be calculated for the two stations from the coefficient of absorption already determined and from the density of iron. We

\again use the exponential forniuki/^-" " flog 11 - lug I^). Substituting

d

the values of /a, d and Kj for Kodaikanal we have

•f»o20.?-- ----- . (log Tk - lo g 2-;ny)5'5 2’5 l X 7 S

or I k- — 2‘C)o7 ion-pairs c m . 's e c .““ ^

Similarly for Agra \\c have

1 \ i ‘025 ion-pairs cm." ' .sec."^

The intensities corresiionding to the altitudes of Agra and Kodaikanal from ComptoiTs intensity-barometei curve for latitudes o'" - 20' " are 2 8 and 17 respec-

m A. K, Das and M. Salaruddin

lively. These values He between those oljtained from the present measurements with and without shield. Hut if we lake into account the fact that Coin])ton*s values are for a shield of 2*5 cm. of bron/.c and 5 0 ciil of lead (which roughly corres])onds to about lialf the thit^kness of the shield used in our experiments), then there is close agiccnient 1)etv\een these \alues and those arrived at in the present i>apei.

1) 1 Ti V N A h V A R 1 A T T O N i ) V C O vS M T C - R A V T N T K N vS T T I K S1 r 11 S 7 n U R 11 A Iv A N I) M K A N 'J' T IM K S

During a number of investigators were engaged in finding outwhether the intensity of cosmic rays varied with sidei'cal time. In 1926W. Kolhorsler and v, v alis from theii observations in Mdnchgipfei in Svvit/.eriaiid found variations up to 15 per cent, following a daily period according to sidereal time with maximum at and ifS'' and miiiimnni at about io \ Later BiUtiiei, Steinmanrer and Steinkc from their observations at different i>laces confirmed the results of Kolh^h ster and v. Salis. Tlic rcvsnlts obtained by different investigators were plotted by A. Corlin ** and are reproduced here in Figure i. As will be seen, all these curves agree wdlli one another excepting those of Lindholm at Mnottas Muraig!. t'orlin * also got the same resvdts as Kolln'irster and others l)y analysing his data at Abisko.

But later observations by a number of olli:*r irn'cstigaiors did not confirm these results. Among the later observations may be mentioned those of R. Steinmanrer at Sonnblick (n}29' o), of Lindholm at Stockholm (1930-, !) and of Compton and others at Mt. l{vans (j()3i). Though tliese investigators did not find any mujucstionable vaiialions in intensity according to sidereal time, yet when their data were analysed and plotted against mean solar time, they found very good agreement in all the curves with maximum a I noon or in the afternoon- These curves arc also reproduced here in Figure 2 from Coilin. ^

1 he intensity data tor Agia and Kodaikanal were analysed aceoiding to sidereal and mean solar times to see how far they agreed with the results of other investigate)!s. lo get tlie mean houily intensity x alnes according to sidereal time, all llie mean times of oirservatioii w'cre converted to sidereal times. Inteusit-bideicul time ciiiws were then dravs'ii for cv'cry day From these curv'cs the intensity values at every sidereal hour weie read off and their means for each hour Axere calculated for Agra and Kodaikanal separately- Similarly mean hourly intensity values xs'ere calculated according lo mean solar lime (in this case Indian Standard Time). These values were plotted sepai alely for Agra aud Kodaikanal and are shoxvn here in Figure 3.

It xvill be seen from Figuie 3 that the mean time curves for Agra and Kodaikanal agree xvith each other and also xvilli those of oilier investigators shown iji Figure 2. Both these curves show a maximum intensity in the afternoon (Agra

Measurement o j Cosmic Rays at Agra and Kodaikanal 199

] he sidereal time pericjd as observed in lyjfi P'lGURU 1

200 A. K . Das and M. Salaruddin

The mean linio jx'riod as observed with elosed shield in

F i g u r e 2

Measurement of Cosmic Rays at .4gra am! Kotlaikanal 201

Uj(JiOiZ

Sidercal-Tinie Curvo.s Mean Time Curves

202 A . K . Das and M. Salaruddin

at 14 ' atid Kodaikanal at 15’') and niiuiiimiu intensities at ir'' and 22''. But the sidereal-tinie curves for these t\so stations do not show any conformity either with each other or with corresponding curves of other investigators shown in I'hgure I. t )n the other hand, a close examination of these two lurvcs shows that they are inoie or less opposite in phase, i.r , the niinimtnn in the curve of one station ct)rresp<Jnding 10 the niaximuin of the other. This can be explained by the fact that the Kodaikanal data refer to the month of February and that of Agra to the months of June July. Between the cot responding sidereal times of I'ebruary and July there is a dilTerence of about 1 j boiUvS according to mean time, and as these curves agree aicording to mean time, they arc opposite in phase according to sideieal time. Therefore, it can be said that the Agra and Kodai­kanal data do not confirm the results of Kolh'hster and others but confirm those of later investigatois who find variations according to mean solar time.

s

8 20 55410 in 14 16 iSIT ours (sidereal)

PKirFE 4But it should lie noted that flic data of Agia and Kodaikanal are very

ircaj^rc to draw any dclinite condusiens. For such kind of work, data ranging over very long peii( ds arc required so as to iniimnib e llic cflcct of abnenna] changes (the so-called variations of the second kind often shown by cosmic-ray ijitensity from hour to hour. These variations of the second kind can be seen from the curves given in Figure 4 where the intensities for two days each for Agra and Kodaikanal are plotted against sidereal time. But in the mean curves shown

Measurement of Cosmic Rays at Agra and KoiaiJ^anal 203

T ad],e I

Solai activity and cosmic-ray intensity (AyraJ

Date

ie -6-36

t<;-6-36

21- 6-36

22- 6-R6

23- 6-36

2.1- 6-36

: 5 - 6 - 3 6

26- n- 6

27- 6-36

2t)-6-36

30-6-36

1- 7-36

2- 7-36

3- 7-36

•1-7-3f>

5-7-36

7- 7-308- 7-36

0-7-36

1 0 - 7 - 3 6

1 1-7 -3 6

1 (-7-36

1.1- 7-36

! 5-7-3''

16- 7-36

17- 7-36

18- 7-36

Daily mean siinspcjt

numbers

60

JOl

88

110

100

76

So

112

68

79

79

74

44

50

52

o

47

43

47

49 67

76

A?69

57

53

KT'loceiili

figure

M , Hrigilt Flour uli

TT.. Dark Flomili

ligiirf

Sum of the 3I'loroulifigures

Mean (lail t'i(Mnir-rav inteust v

2.8 2.8 .3 7-9 *■3113 0 2.y -■ 5 8.4 1.326

3-0 3.0 2.2 8 2 3.214

3-1 2.S 1.8 7-7 1.568

2.0 3 2.: 8.1 *•475

3 2.7 2.0 7-7 *-544

3 r 2.8 2.4 8 3 *-5- 53-2 3-t' 2.5 <8.7 1.622

3-' 2.2 8 8 1.512

3 2 3-5 2.8 0 5 1.62 32.8 27 2.8 8-3 * 38.

2,8 2.8 3-2 8 . 8 1.500

2.9 7.0 3.0 8.9

3-f> 3-0 3-0 9 0 •5\S

2.9 2.0 2,8 7-7 3.596

2 . g , 27 3-0 8.6 1.616

2 . 8 2.8 2.2 7.8 1.670

2 . S 2.0 2.1 6.6 * 5372.4 2.0 2.0 6.4 1.561

2 . 6 2.1 1.8 0.5 1 571

2 . 8 1-5 T-5 5-« *-57-»

2 , 1 1 2.0 2.0 6.1 *-.S742 9 2.2 1.0 6 1 3.502

2.9 2,5 I , u 6,4 3.692

3-' 2.7(

T . O 0 . 8

3-1 11 . 0 69 >•37''

2.9i ”

1.0 6.7 1.576

31 j 3 0 1 0 7-J 1.566

204 A. K. Das ami M. SalurudtUn

'I'aui.k

Solar ai-tivity and cosiiiif-iay iiiicnsily M\odaikana])

; in.nilDnk‘ (

I li'4uu

g”2‘3S

10-2-38

1

1“) .'"30

17".;."3S

n)“. 3S

::n~4*3S

131-3-38

foi

'33

' 3 7

mi

1(H)

171

'71

'43nS

IOlj

K1'1( x'cnli rit'iiic

3-4

3- -'

38

3."

4- '

4 1

4 4

4-1

4-1

3 4

3-*''

3--'

II „I*](M (111i (iin'i

3.S

4 "

3 -1

4‘-’

4

3 "

‘ *

5 <'

1 -

S.n

1-1

,l.u

3'3

TI „ 1 )nl l ! r»f tlu' 3iMui I iili I'lgim-

:2 8

3’3

3

4-3

3 7

5 «'

I Hoi c xili ligiirc

S.7

10. (J

TO 0

J3 5

11 .S

14 3

13 1

11 -I

11. -1

II 4

10,ti

in.o

g.6

Moan tlailv rosniic’-ray iiilonsitv

3 . 3 1 1

2- 313

2.37(1

2 3' H

->3'-)3

‘-•34 '

3- 331

2.3 S3

2 333

2.342

2.379

in l 'iguri-3 lliosc variations are inueh less proiiouiicLM and if longer periods are taken the curves may lie expected to become very much smoother.

C O ft M 1 C U \ V ft A N 4) ft O I, A K A C 4' I 1 4' V

Wlielher tlie sun at idl contributes to tlie iiiteOvsity of cosmic rays docs not Seem to have been conclusi 'e^y established. Some observers have, however , claimed lo have detected a .small solar conti ilnition as the result of theii analysis of a long series of measiirements. Another way of detecting solar influence on eosmic-ray intensity is to correlate the mean tlaily intensity witli solar activity. Accordingly the mean daily cosmic-ray intensities, for Agra and Koclaikanal were calculated Irom the values of I,) and tlie suns[K)t numbers ami flocculi tigiires were taken Irom tlie quarterly bulletins for cliaracter figures of solar iilieuomeua t'ublished under the auspices of the Inteniatioiial AvStroiiomical Union. In the bulletins the llocculi figures are given separately for calcium flocculi, bright markings and Ha dark markings, each for tlie whole disc and for tlie inner circle (half the radius of disc) of tlie sun. Tlie sum of tlie three ‘ \\hole disc ’ figures was taken

for the purpose of correlation. All these results are collected in Tables i and 2 for Agra and Kodaikatial respectively. These figures were plotted as dot diagrams in order to see whether any relationship exists either betw een the intensity and flocculi figures but no relationship of any kind was detected. The data considered are, how’ever, very meagre for drawing any definite conclusions.

The senior author takes this opportunity of thanking Dr. C. W. B. Normandy C.I.E., Director-General of (Observatories, for imrchasins the Kolliorster apparatus at his request. He is indebted also to Rai Bahadur G. Chatlerjee, Superintending Meteorologist, Agra, who had the iron shield constructed at the Agra Observatory besides providing him with all facilities for the i>art of the work done at Agra and Dr. N, K . Sur, Meteorologist, for the valuable assistance he gave him in the reduction of the cosmic-ray records at Agra (Jur thanks are also due to Dr. A. ly- Narayan, Director of the Kodaikanal Observatory, for his interest in the part of the work done at Kodaikanal.

Measurement of Cosmic Rays at Agra and Kodaikanal 205

R E B E R B N C K S

A. H. Compton, Phys, Rev. 43, 387 (1933).I. S. Bowen, R. A. Millikan and H. V. Nelier, Phys. Rev., 82, 80 (1937)- A. K. Das, Nature, 136, 39 (1933),A. Corliu, Annals Lund Obs., No. 4, P. A, 56 (1934).R. A. Millikan and G. II. Cameron, Nature, 121, 19 (1928) and PUy$. Rev., 37, 335 (1931)- A. Corliii, Annals Lund Obs., No. 4, V, A. 15 (1934).Ibid., P. A, 110.Ibid,, P. A. 19.