Electrons by Metals under Influence of Alpha Rays. 4GT) 



used previously, the saturation value of the current had been 

 obtained with 4- 40 volts on the case. With the platinum, 

 an hour after the liquid air had been applied to the charcoal, 

 it required -f 160 volts to cause saturation, and the current 

 at this potential was 20 per cent, greater than at 40 volts. 

 Four hours later 120 volts was sufficient to cause saturation, 

 and the current was only 12 per cent, greater than at 

 40 volts. After an interval of 24 hours, saturation was 

 reached at 80 volts with a 5 per cent, increase over 40 volts. 

 During the same time the magnitude of the current (taken 

 under similar conditions) fell off about 30 per cent. But the 

 shape of the ionization curve, obtained by using a saturating 

 potential and interposing aluminium foils, changed very 

 little, if at all, while these very considerable changes were 

 going on in the conditions of saturation and in the actual 

 magnitude of the current. The results are given in Table I. 

 The first line of the table gives the time after the liquid air 

 was applied to the charcoal bulb, the second line gives the 

 value of the currents (with two toils interposed) correspond- 

 ing to these times ; the last five lines of the table give the 

 values of the current when different numbers of foil are 

 interposed, the current with two foils being taken as 100 in 

 each case, to facilitate comparison. 



Table I. 



Time 



lhr. 



2 hrs. 

 174 



4 hrs. 



6 hrs. 



24 hrs. 



C 2 



186 



150 



1465 

 100 



129 



100 



Foils 

 2 



100 



100 



100 



3 



112-0 



111-2 



112 3 



1130 



111-8 



4 



103-8 



103 



105 



103-3 



104-7 



5 



59-5 



60-3 



64 



63-7 



662 



6 



231 



23 



25-3 



25-6 



26-6 



It will be seen that the relative values for 2, 3, and 4 foils 

 show no progressive change with the time ; the differences 

 between them are of the order of magnitude of the experi- 

 mental errors. The values for 5 and 6 foils, however, appear 

 to increase with the time ; these values are on the decreasing 

 portion of the ionization curve, where a small change in the 

 range v of the a-rays makes a large difference in the current. 

 The observed increase can be explained by supposing that 

 the progressive removal of occluded gas from the platinum 



