of Radioactive Products present in the Atmosphere. 835 



we obtain 



N E = '090, at the height o£ the upper wire, and 

 N E = -082, at that of the lower ; 



^—, =13,000, for the effective region of the upper wire, 

 E i. <?., in the vicinity of the height of 6*5 



metres above the ground, and 



6,500, for that of the lower wire, ?'. e., in the 

 vicinity of the height of 1'5 metres. 



The greater value of N E corresponding to the upper wire 



4M 



N, 



implies that the condition w s 



has not been quite' 



y -415 x k 



satisfied during exposure. Taking a roughly estimated cor- 

 rection due to this cause into account, we find 



Ne = about '1. 



Discussion of the Results. 



(1(5) The amount of the radium emanation in the atmo- 

 sphere is to be directly measured, either by absorption in 

 coconut charcoal or by condensation at the temperature of 

 liquid air, as has been done by Eve*. Ashman |, and Satterly %. 

 Their results are shown below. 



Table II. 



Observer. 



Average amount of 



radium emanation 



per cubic metre. 



Ratio of the 



extreme 

 values. 



Locality. 



Eve 



GOxlO curies 



soxicr 12 „ 



105X10" 12 „ 



7 :1 



4-4:1 



10 :1 



Montreal 



Chicago 



Cambridge 



Ashman 



Satterly 



Taking the mean of the above three, the average amount 

 of the emanation in the air near the earth's surface becomes 



83 x 10 ~ 12 curie per cubic metre, 

 which corresponds to about 1*4 atoms of the emanation per 

 c.c, ?'. e., about 14 times the value we have calculated. 



* Eve, Phil. Mag-. Oct. 1908. 



-]■ Ashman, Amer. Journ. Sci. vol. xxvi. (1908). 



X Satterly, Phil. Mag Oct. 1908 and July 1910. 



