214 



Mr. G. C. Simpson. 



[Feb. 3, 



The first few measurements which I made having shown that 

 the radio-activity is very much greater than in lower latitudes, I 

 determined to make a thorough investigation of it. On November 23, 

 I started a series of measurements of the radio-activity, taking three 

 observations a day ; the first in the morning between the hours of 

 9 and 12, the second in the afternoon between 3 and 6, and the third 

 in the evening between 9 and 11 ; the series continued uninterrupted 

 for 4 weeks. The results are given in full in Table I, when the follow- 

 ing symbols are used : 



B = height of barometer in centimetres. 



T = temperature in Centigrade degrees. 



W = estimated velocity of wind, the direction being added. 



P = potential gradient measured in volts per metre. 



It will at once be seen that the numbers are very much higher 

 than the corresponding ones for Germany, the mean for the month 

 being 102, which is nearly six times as great as the German mean 

 (for the year) ; and the highest value, 432, being nearly seven times 

 greater than the German highest. To turn now to a closer investi- 

 gation of the numbers, Table II shows that there is a marked daily 

 period. 



Table II. — Mean and Maximum Values of A for each Week. 









* 













Morning 



Afternoon 



Evening 







A. 



A. 



A. 



Mean 

















of 

















three. 





Mean. 



Max. 



Mean. 



Max. 



Mean. 



Max. 





Nov. 23 to Nov. 28 . . 



62 



114 



86 



150 



146 



294 



98 



Nov. 30 to Dec. 5 .*. . 



71 



144 



69 



120 



82 



228 



74 



Dec. 1 to Dec. 12 . . . 



105 



168 



68 



90 



129 



198 



101 



Dec. 13 to Dec. 19 . . 



110 



204 



131 



384 



166 



432 



136 



Mean for month . . . 



87 





88 





131 



| 102 



The maximum falls in the evening, there being little difference 

 between the morning and afternoon means. Not only is the mean 

 value greatest for the evening, but the absolute maximum falls in the 

 evening each week, and on 13 out of 22 days on which three observations 

 were taken the evening values were the greatest. 



It would be of interest to find the relation, if any, between the 

 radio-activity and the other electrical conditions of the atmosphere; 

 but my observations of the dissipation and the ironisation of the air 

 are not sufficiently complete for a rigid comparison, and so must be 



