﻿in the Earth and the Atmosphere. 197 



not altogether in good agreement with those found by several 

 other observers. 



In the lead vessel there were 95 ions generated per c.c. 

 per second. In the case of all the other metals examined, 

 there were 21 ions per c.c. produced per second. No differ- 

 ence could be detected between clean zinc, copper, aluminium, 

 iron, tinned iron, and aluminium in lead. It was natural to 

 suspect that the lead was coated with radioactive matter, but 

 after cleaning it with emery-paper and washing it with 

 hydrochloric acid, there was no diminution in the value of g. 

 On the other hand, when the lead was lined with aluminium 

 *4 mm. thick, q was equal to 2-1. My results appear to agree 

 with the work of other observers in the case of lead, for which 

 all agree in finding a high value of y : and the effect is 

 certainly not due to a surface-deposit merel} r . It was also 

 found impossible to lower the value of q for zinc by a cleansing 

 treatment of the surface. It appeared possible, from 

 Campbell's work, that the results obtained in these experi- 

 ments might be due to an accidental relationship between 

 volume and surface. Cylindrical rolls both of aluminium 

 and copper were therefore compared, 51 cms. long, having 

 diameters 23, 17, O'S cms. successively, and the central wires 

 or rods were charged to potentials varying from 150 to 120 

 volts. The results obtained for copper and aluminium, under 

 any similar conditions, were identical in each case. 



If the ionization is due to intrinsic radiations from the 

 metals, it is extraordinary that so many different metals should 

 give equal values. If the ionization is due to radioactive 

 impurities in the metals, it is no less strange that tiie impurities 

 should be distributed in so uniform a manner. 



Corrections amounting to 7 or 8 per cent, were made for 

 the current across the small electroscopes, after deducting 

 which the results were those given in column I. 



Table III. 



Metal. 



Density. 



Thickness 

 in mm. 



Natur 



Ionizat 



il 

 on. 



Artificial 

 Ionization. 



Q. 



Lead 



Lead in lead... 

 Tinned iron ... 

 Copper 



11-4 



11-4 



8-8 

 7 2 



7-0 

 2i'» 

 2-6 



•4 



1-6 



- 7 

 '4 

 •67 

 ■6 

 •37 

 •4 



in 16 



95 

 ( .)5 

 24 

 24 

 24 

 24 

 24 

 24 







550 

 482 

 448 

 345 

 320 





851 



Aluminium ... 

 Al. in lead 



207 

 244 



