314 Bumstead and McGougan— Emission of Electrons by 



§ 2. Determination of the Ionization Curves of Various Metals. 



In the determination of the ionization curve of platinum in 

 the preceding section and of those of gold and aluminium in 

 the previous paper, the metals were so thin that the a-rays 

 passed through them, except when they were near the end of 

 their rauge. This has the advantage that, at least until the 



Fig. 1. 



CENTIMETERS 



top of the curve is reached, no correction for the charge of the 

 a-rays is necessary and one need not apply a magnetic field in 

 order to determine this charge. On the other hand, a difficulty 

 results if one wishes to make a careful comparison of different 

 metals. It is impossible to obtain foils of different metals 



