[mclennan-mcleod] EARTH'S PENETRATING RADIATION 37 



of 4- 1 ions per cc. per sec. was obtained for ''q" by Simpson and Wright 

 with a zinc receiver of about 27 litres capacity, and a value of 4 ions 

 per cc. per sec. by the wi'iters with an ionisation chamber of the same 

 metal of only 2 litres capacity, one is led to the conclusion that the 

 experimental results obtained so far lend no support to the view that 

 the residual ionisation obtained in ah confined in zinc receivers is due 

 to a radiation emitted by the walls. It would be interesting however to 

 see what resulted if receivers of still smaller capacity than two litres 

 were used. On the other hand it has been shewn by J. J. Thomson* 

 and again recently by Langevin and J. J. Rey f that one cannot account 

 for this residual ionisation by supposing it due to collisions between the 

 molecules, for on this hypothesis, the increase in ionisation with a rise 

 in temperature should be enormously greater than any increase which 

 has been observed. 



The wi'iters wish to acknowledge their indebtedness to Messrs. 

 P. Blackman, G. S. Campbell, and E. C. Henderson for their kindness 

 in making corroborative measurements at various times during the 

 investigation. 



The Physical Laboratory, 



The University of Toronto. 



*J. J. Thomson, Conduction of electricity through gases, p. 294, 2nd ed. 

 tLangevin and J. J. Rey, Le Radium, April, 1913, p. 139. 



