311 



fall towards low values and then a rather sudden rise. An increase in flow 

 is accompanied by an increase in radioactivity. 



The increase of flow follows the melting of a heavy snow or a heavy rain. 

 Thus the radioactivity of the spring depends upon the rain fall. The radio- 

 activity of rain water is very small compared to the values obtained at the 

 springs. Tt can not be due to the radioactivity of rain water. 



The above results, together with the fact that "wet weather" springs are 

 very radioactive and that one on the campus of Indiana University measured 

 1920 xlO- 12 a short time after a heavy rain fall, lead to the conclusion that the 

 variation of the emanation content of Indiana springs is due to the rain water 

 percolating through the soil and dissolving and carrying down with it some 

 of the emanation which is continually moving upwards from the interior of 

 the earth to the surface. During dry weather when the flow of the water is 

 not rapid a large per cent of the emanation which was dissolved in the water 

 is transformed into radium A, B, C, and D before the water issues from the 

 ground. 



This conclusion is in accord with the observations of Wright & Smith 

 (Phys. Rev. Vol. 5, p. 459, 1915) in which they find that the amount of 

 emanation which issues from the soil is decreased as much as 50 per cent at 

 times after heavy rains. 



To recapitulate, the variation of the emanation content of spring water is 

 due to the rain water dissolving emanation as it percolates through the soil. 



Department of Physics, Indiana University, December 1, 1915. 



TABLE I. 



Variation of the Emanation Content of Certain Springs near Bloomington 

 Indiana. (Flow given in gallons per day.) 





Hottle Spring. 



Illinois Central Spring. 



Date. 



Temp 

 C. 



O 



Flow. 



Curies 

 per Liter. 



Temp . 

 C. 



O 



Flow. 



Curies 

 per Liter. 



1914. 



Sept. 24 



Oct. 16 



Oct. 23 



Oct. 30 



Nov. 6 



13 



13 



13.3 



13 



13 



10000 



650xl0- 12 



695 



700 



665 



650 



12. S 

 13 



12.7 

 12.6 



130000 



445x10 '-' 



166 



120 



20 



40 



