[WRIGHT] VARIATIONS IN THE CONDUCTIVITY OF AIR 105 



for the corresiJonding effects due to the earth's radiation were 1.1 to 1.23 

 to 1.00. The considerable difference beween these ratios would thus 

 seem to indicate a difference in penetrability between the y rays from 

 radium and the penetrating radiation from the earth. It is possible, 

 however, that the discrepancy may have had an entirely different origin 

 and further measurements should be made to ascertain the cause of it 

 before a satisfactory explanation can be offered. 



VII. — Experiments on Absorbing Power of Water. 



From the foregoing experiments with radium in conjunction with 

 the effect noticed in IV c, we f-^e that tliere was in each case some 

 additional effect inside the cylinder which must be considered as due 

 to the presence of the wall. From these experiments the idea presented 

 itself that possibly the earth's penetrating radiation was the same at 

 all points on its surface, and that the differences observed in the values 

 for " q " for the land and water experiments were due not so much 

 tc differences in the absorbing power of the different soils as to dif- 

 ferences in a secondary radiation induced in the crust of the earth by 

 this penetrating radiation. 



To determine if any effect of this kind could be noted in the case 

 of water ior the penetrating rays from radium, the sample used in the 

 investigation described in Section IV was lowered under the ice on 

 Grenadier Pond, and the ionization noted in a lead cylinder placed above 

 it for different depths of the radium. In making these measurements the 

 radium was hermetically sealed in a glass tube, wliich was then enclosed 

 in a tube of brass, whose walls were 1 cm. in thickness. 



The results (Table XIII) shewed that 2 metres of water completely 

 cut off all effect from the radium — both primary and secondary, the 

 same being illustrated by the curve in Fig. 9. 



TABLE XIII. 

 Cylinder 113 cms. above ice. 



