Atmosphere 



atoms by sunlight and 

 these might account for 

 waves during the daytii 

 sun seems to be mainly 

 atmosphere, so that it; 

 near the earth's surface 

 this point. 



due to Radioactive Matter. 37 



then returned to the parent atoms, 

 the greater absorption of the Hertzian 

 ne. The ultra-violet light from the 

 absorbed in the upper layers of the 

 is not an important ionizing agent 

 . Further observations are needed on 



Effect of Altitude, 



In conclusion we have to discuss the effect of elevation on 

 the radiation from the radium C in the earth. The 7 rays 

 are absorbed rapidly in the earth, slowly in the air, and the 

 ratio of the coefficients of absorption is nearly that of the 

 densities, or as 2*7 is to *0013, about 2000 to 1. So that 

 1 cm. of the soil is as effective as 20 metres of air. In the 

 case of a point source of radium C the law of inverse square 

 of the distance also obtains, so that the radiation at a distance 

 r from the source varies inversely as r 2 e Kr . Hence if with 

 such a point source the radiations were represented by 100 

 at 1 metre, there would be a rapid decrease with distance 

 thus 



At 1 metre, radiation 100. 

 10 „ „ '95 



100 „ „ -0064 



1000 „ „ -000012 



But in the case of the earth we have a sheet of radioactive 

 matter, distributed with some approach to uniformity through 

 the surface layers, which alone is effective in the atmosphere. 

 The calculation has not, I think, yet been given, and therefore 

 it is set forth here with some fulness. 



Let P (fig. 1) be a point at elevation h above the earth's 



S an* 



OC *■■•' A earth 



surface, assumed plane. Let Q grammes of radium be the 

 contents per cm. 3 in the earth. Consider an elementary ring 

 dx by dY , radius a, at a depth Y below the surface. Then. 



