1S4 Sanderson — Soil and Atmospheric Radioactivity, 



of radium. This is one four-thousandth the amount found for 

 underground air here at New Haven. The average of Joly's 

 values* for the thorium content of many common rocks is 



approximately ten times the value found from the emanating 

 power for the thorium content of the earth at New Haven, 

 while his value for the radium content is about one hundred 

 times that found for New Haven earth by the method employed 

 in this paper. 



Summary. 



A determination has been made of the amount of radium 

 emanation in the underground air in the neighborhood of the 

 Sloane Physical Laboratory. It was found that one cubic cen- 

 timeter of underground air contains radium emanation equal 

 to the amount in equilibrium with 2-4 XlO -13 gram of radium. 

 This is equivalent to the production, per cubic centimeter of 

 earth, of radium emanation in equilibrium with S*9xl0 -11 gram 

 of radium. 



A method has been devised by which the amount of thorium 

 emanation preseut in underground air can be directly measured 

 in an electroscope and compared with the emanation evolved 

 by a known weight of thorium salt. In this manner it was 

 found that the earth in the neighborhood of the Laboratory 

 emits per cubic centimeter thorium emanation equivalent to 

 that produced. by 1-35X10 -6 gram of thorium under the stand- 

 ard conditions. 



The important bearing of the emanatiug power of the soil 

 on the radioactive properties of the atmospheric air in different 

 localities has been pointed out, and a method has been sug- 

 gested by which the emanating power of the soil and the 

 radioactive character of the underground air can be determined 

 in any given locality. 



In conclusion, I wish to acknowledge my very great indebted- 

 -o Professor B. P>. Boltwood. and express my thanks for 

 his assistance and advice. 



Sloane Physical Laboratory, May, 1911. 



* Phil. Mag., xviii, 140, 1909. 



