in the Atmosphere near the Eartlis Surface. 729 



collected over water. The gases thus obtained from one tube 

 were nearly sufficient to fill the electroscope. After several 

 trials, a uniform speed of 6*7 c.c. per second, and a period of 

 2*7 days were adopted ; so that the total amount of air drawn 

 through tube A was 1*56 cb.m. The amount of emanation 

 collected in tube A was usually about 20 per cent, greater 

 than the amount in B or C. The total amounts obtained in 

 the three tubes added together are given in the following 

 table : — 



Date. 



Divisions per minute. 



Run. 



Best. 



July 10 



•331 



•383 

 •335 



•390 



•373 

 •360 



•251 

 •221 



•243 

 •233 



„ 13 



„ 16 



,, 19 



, 25 



„ 29 



.Aug. 1 



3 



6 



„ 9 





Thus the mean of the "runs" was "362 and of the "rests" 

 •237, with a difference of *125 D/m. The fluctuations in value 

 of the middle column are in excess of experimental errors, and 

 indicate that the amount of emanation in the air at Montreal 

 in July was varying between maximum and minimum values 

 in the ratio of 7 to 4, approximately. This variation is small 

 compared with that observed in the active deposit collected 

 from the atmosphere, for which the corresponding ratio is 

 16 to 1. This wider divergence is probably due, not to 

 a change in the amount present, but to the meteorological 

 conditions existing during the time of collection. 



The charcoal in the tubes was next calibrated with standard 

 solutions, three in number, of strengths 10~ 10 , 1*57 x 10' 



and 1-57 x 10" 7 

 above. 



The method was the same as that described 



Strong Solution. 

 The tubes gave 



A. B. 



57 22 



1-57 xl0~ 7 gram. 



C. Total. 



25 104 divisions a minute. 



In this case about 20 per cent, of the possible maximum 

 was absorbed and given off by heating. It is noteworthy 



