Metals under the Influence of Alpha Rays. 313 



measurements were taken as before. Then the strip was 

 heated five times, for ten minutes at a time, with intervals of 

 fifteen minutes between, to avoid too great heating of the 

 clamps and copper rods : the pump was kept running contin- 

 uously. Measurements of the S-ray current were then made as 

 before. The results are given in Table 2. 



Table 2. 





Before 



After 



Foils 



C 2 = 150 



C 2 = 134 



2 



100 



100 



3 



no- 



108"2 



4 



102 -1 



101-0 



5 



62-5 



61-0 



6 



24-7 



24-2 



Here there does appear to be a slight alteration in the form 

 of the ionization curve, and in the direction expected. But 

 the differences are so slight that no great confidence can be 

 placed in the result. Further experience with the method did 

 not give any reason for hoping that the question as to the 

 effect of adsorbed gases could be definitely settled in this way. 



The results of this experiment are susceptible of two quite 

 different interpretations. We may say that, since the heating 

 of the platinum strip did not alter the shape of its ionization 

 curve, we may conclude that this shape is due to the properties 

 of the metal itself and not to adsorbed or occluded gases. On 

 the other hand, we may put the emphasis on the fact that, 

 under certain conditions, at least 30 per cent of the S-ray 

 effect is due to such gases, and that when these are removed 

 there is no change in the shape of the curve. If the residual 

 effect is really due to the metal we must suppose that platinum 

 and the adsorbed gases have ionization curves of very nearly 

 the same shape, which is not altogether probable considering 

 the variations which are met with in the curves of gaseous 

 ionization. From this point of view, therefore, it seems more 

 probable that the S-ray emission (slow electrons) is mainly 

 due to such a layer of gas, which may be reduced but not 

 entirely removed by the methods which we have employed.* 



* Since the present investigation was completed, a paper has appeared 

 (Pound, Phil. Mag., xxiii, 813. May, 1912) in which the effect of occluded 

 gases upon the magnitude of the ^-radiation is clearly brought out. 



