NOTE ON PENETRATING RADIATION MEASUREMENTS OF THE CARNEGIE'S SEVENTH CRUISE 



Measurements of penetrating radiation, or cosmic 

 rays, were made regularly on cruise Vn with apparatus 

 no. 1 mounted in the atmospheric-electric house. The 

 apparatus and the observational procedure have been 

 discussed in section n, pages 13 to 15. Apparatus no. 1 

 was used also on earlier cruises of the Carnegie , but foi 

 the seventh cruise was improved in several respects, 

 the most important improvement being that made to the 

 "balancing condenser" (page 13). Although more than 

 three hundred measurements of penetrating radiation 

 were made on each of cruises IV and VI, accurate values 

 of penetrating radiation itself, in terms of ion-pairs per 

 cc per second in the free atmosphere, were not obtained, 

 owing to uncertainty as to the amount of "residual" ion- 

 ization of the apparatus. From study of both sets of 

 data, Mauchly (1) estimated the residual ionization to be 

 about 2 ion-pairs per cc, and it was hoped that on cruise 

 VII a more accurate value could be determined. 



To determine the residual ionization on cruise VH, 

 a second apparatus, small and portable, designed by Dr. 

 Kolhorster and numbered 5503, was supplied to the Car- 

 negie at Hamburg, Germany, in July 1928. This appara- 

 tus was so designed that its residual ionization could be 

 determined by immersion in a sufficient depth of water, 

 and, having such a determination, comparative measure- 

 ments between apparatus 1 and apparatus 5503 would be 

 expected to jrield values of residual ionization for no. 1. 

 The progress reports in section HI go far to explain why 

 this expectation was not realized; difficulties were con- 

 stantly arising with apparatus 5503, the chief difficulty 

 being that of displacement of the "charging arm" within 

 the chamber of the apparatus, which affected the con- 

 stants and oper ability of the instrument. The final result 

 of much instrumental adjustment and manipulation, and 

 several intercomparisons, was abandonment of the work 

 with apparatus 5503, so that satisfactory determination of 

 the residual ionization of apparatus 1 was not obtained. 



Some indication, nevertheless, may be obtained of 

 the magnitude of the residual ionization from the very 

 earliest intercomparison observations between no. 5503 

 and no. 1 if, as seems probable, instrumental difficulties 

 had not yet developed in the first two weeks after no. 

 5503 was received. The Carnegie left Hamburg on July 

 7 and arrived at Reykjavik July 20; on each of eight days 

 from July 11 to 18, inclusive, a daily intercomparison 

 was made and the values of R (ion-pairs produced per 

 cc per second inside the chamber of the apparatus) for 

 the two instruments show reasonably consistent differ- 

 ences from day to day. The data are shown in table 1. 



When apparatus 5503 was supplied to the Carnegie 

 at Hamburg, Dr. Kolhorster gave the value of residual 

 ionization of that instrument as 1.3 ion-pairs per cc per 

 second. This figure had to be corrected later to 1.6 ion- 

 pairs when he corrected the value of capacitance of the 

 apparatus by a factor of 1.243. 



With the residual ionization of 1.6 ion-pairs per cc 

 per second for apparatus 5503 and a difference between 

 no. 1 and no. 5503 of -0.1 ion-pairs, the value of the re- 

 sidual ionization for apparatus 1 appears to be 1.5 ion- 

 pairs per cc per second. This result will be seen to be 

 a satisfactory value, when the penetrating radiation data 

 for cruise VH are examined. 



Table 1. Intercomparison observations with Carnegie 



penetrating radiation apparatus no. 1 and Kolhorster 



apparatus no. 5503, from July 11 to 18, 1928 



The observations of penetrating radiation, or cos- 

 mic rays, made on cruise VH are tabulated in section IV, 

 where 368 values are given. Each value is the result of 

 approximately one hour of measurement with apparatus 



1, usually only one measurement being made each day 

 in midafternoon, the time of measurement being made 

 to coincide as closely as possible with the time of ob- 

 servation of other atmospheric-electric elements. On a 

 few occasions several measurements of penetrating ra- 

 diation were made on the same day; all '^ues obtained 

 on these' occasions are given in section IV. 



The grand average value for the 368 values is 2.8 

 ion-pairs per cc per second, and when a residual ioniza- 

 tion of 1.5 pairs is deducted, the value of 1.3 ion-pairs 

 per cc per second produced by cosmic rays in the at- 

 mosphere near the earth's surface is in good agreement 

 with the now generally accepted value. 



When the observations are grouped according to 

 geographic latitude there is some indication that for the 

 northern hemisphere the values in high latitudes are 

 larger than the values obtained in equatorial regions, but 

 the results for the southern hemisphere do not give the 

 same indication, at least to latitudes as high as 40° south. 

 These remarks are based on the data presented in table 



2, where the average value is given for each group of 

 penetrating radiation measurements made in each 10- 

 degree latitude belt between 60° north and 40° south. The 

 number of measurements in each group is also indicated. 



When the Atlantic Ocean data are regrouped under 

 only two latitude ranges, namely, 0° to 30° north, and 

 30° to 64° north, the average values of penetrating radi- 

 ation for these groups become 2.61 and 2.94 ion-pairs, 

 respectively, the value for high latitudes being 12 per 

 cent greater than that for low latitudes. When the data 

 for the northern hemisphere of the Pacific Ocean are re- 

 grouped similarly, the high latitude value of 3.02 ion- 

 pairs is found to be 4 per cent greater than the value of 

 2.89 for low latitudes. For the southern latitude data in 

 the Pacific Ocean, on the other hand, a value of 2.7 ion- 

 pairs per cc per second satisfactorily represents the en- 

 tire range of latitude in which measurements were made, 

 namely0°to 40.°4 south. Subtracting the residual, 1.5ion- 

 pairs, from the various values just given, high northern 

 latitudes give values of 1.4 or 1.5 ion-pairs, low latitudes 

 give values of 1.1 to 1.4 ion-pairs, and southern latitudes 



157 



