(etals under Influence of Alpha Bays. 



The close similarity observed with the two metals gives rise to 

 the suspicion that the electrons we have been measuring are 

 emitted not from the metals themselves, but, perhaps, from a 

 layer of adsorbed gas which is the same in both cases. I have 

 uot yet had an opportunity to test this possibility, or to obtain 

 the " ionization curves" of other metals, but I hope to do so 

 shortly. The observation of Aschkinass (p. 414, foot note) 

 seems to indicate that copper and aluminium would not give 

 identical results. 



Conclusions. 



1. The emission of electrons by aluminium and gold foils 

 under the influence of a-rays (secondary S-rays) varies with the 

 speed of the a-rays in a manner entirely analogous to the 

 variation in the gaseous ionization produced by a-rays. The 

 emission at first increases and then rapidly decreases as the 

 a-rays near the end of their range, and the curves obtained 

 show all the characteristics of the ionization curves in gases 

 first obtained by Bragg. 



2. The curves lie within (to the left of) the corresponding 

 curves for gases and have a less conspicuous " knee." So far, 

 they are in agreement with the known results on the retarda- 

 tion of a-rays by metals, and with the hypothesis that the loss 

 of energy by the a-particles is due to an ionization of the 

 metallic molecules. But the close similarity in the behavior of 

 gold and aluminium is not in accordance with this view. 



3. In view of the dissimilarity in the ionization curves of 

 different gases, the agreement in the curves obtained for 

 aluminium and gold is unexpected, and leads to the suspicion 

 that the observed effects may not be due to the metals them- 

 selves, but, perhaps, to a layer of adsorbed gas in both cases. 

 A further investigation of this will be undertaken shortly. 



Sloane Laboratory, Yale University, August, 1911. 



