100 



THE ROYAL SOCIETY OF CANADA 



that if we take No = 3 ions per cc per sec. to represent the effect of pene- 

 trating radiation at the earth's surface and make use of the constants 

 cited at the beginning of the present section we obtain a value of Q 

 of the correct magnitude, thus affording evidence of the origin of the 

 penetrating radiation as due chiefly to the radium content of the soil. 



Figure 1 



On the other hand, observations made during balloon ascensions have 

 failed to reveal the gradient required by theory: these are discussed 

 in the next section. The gradient of the penetrating radiation above 

 earth's surface is calculated from (2), and below the surface from (4) 

 making use of the numerical tables in the paper previously cited: the 

 results are tabulated below and are shown graphically in Fig. 1. The 

 intensity at the earth's surface is taken to be unity. 



