Properties of Thin Films of Platinum. 123 



altered in various ways to find whether the ratio could be 



E 



changed. Measurements of =p- currents were made : — 

 & I 



1st. With the apparatus as already described, just after 



depositing a film. 

 2nd. At atmospheric pressure, and at various pressures 



down to a liquid-air vacuum. 

 3rd. By varying the potential of the walls, but so as to be 



always high enough for the current to be on the 



part BC of the distribution curve. 



Fig. 5. 



4th. After standing in air for a few days. 



5th. After removing the platinum electrode G from the 



apparatus altogether to find whether light reflected 



from it had an influence. 

 6th. With the platinized walls covered with soot to be 



absolutely sure that reflected light from the walls 



had no influence. 

 None of these modifications produced any appreciable 

 change in the ratio 1*26, so that the conclusion can be drawn 



that this maximum ratio y can have larger values than 1*14 

 given by Stuhlmann. 



8. Influence of different sources of Light. 



It was at first intended to investigate the influence of the 

 wave-length of the light used on the dissymmetry. It is very 

 probable that this has some influence, for the velocity of the 

 photoelectrons depends on the frequency. Millikan * has 

 recently shown that there is a method for varying the velo- 

 cities of the photoelectrons which gives much wider ranges 

 than can be obtained by sifting out the different frequencies 

 from a mercury lamp. Whilst the arc can only produce 

 velocities up to about 3 volts, by using a spark as source of 

 light, velocities can be obtained as high as 500 volts. If the 

 velocities of the electrons affect the dissymmetry, this will be 

 * Verh. d. deutsch. Phijs. Ges. No. 14, p. 712 (1912). 



