[eve] radioactive SUBSTANCES IN THE EARTH 137 



Many readings were then taken of the natural ionization, when 

 the radium was removed, with the electroscopes both within and without 

 the lead and wood box. The average difference was q = 1 • 1 for a copper 

 vessel 2 mm. thick. If this difference is 34 per cent, of the total pene- 

 trating radiation, then the full value for a copper vessel is, 3-2 and for 

 an aluminium vessel 2' 7. 



This is a low value for the penetrating radiation, but it will be 

 remembered that the Saxicava Sand has a low radium content. It 

 might well be that in other localities the value of q for the penetrating 

 radiation might be as much as 3 or even 6, as other observers have 

 found. The method here described appears to be promising, the only 

 drawback being the great weight of the box. 



In conclusion it may be added that there was evidence of diurnal 

 variations, which has not however, yet been studied. A comparison 

 is needed between two vessels side by side, the one closed, the other 

 hermetically sealed. 



Sec III, 1913—9 



