Ionization of Platinum by Cathode Rays. 293 



curve represented by curve B (state B) it was as great as 

 Ab volts. 



Fig. 2. 

 20 



-R 1 



- " '■ I ... T ... 



1 







/ 

















__J- — 1 — j-4 — f^^^ 









'"' 



O / 2 3 4 6" 6 ? 8 51 to II a j 

 V - V * SfuuLcL erf Hays 



Xo 



30 



In determining the effect of the subsequent history of the 

 platinum the complete curve, similar to those of fig. 2, was 

 not traced. Three quantities only were measured: — (1) R Hl ', 

 the value of R' for the minimum just before the ionization 

 potential ; (2) W, the speed of the rays corresponding to the 

 ionization potential ; (3) Z=(I W — I*>)/Iwj where I w and I 20 

 are the values of I when the speed of the rays are Wand 20 volts 

 respectively. Z has no special significance, but it measures 

 with sufficient definiteness the form of the curve ; it was 

 found that, in the range shown in fig. 2, the curve for which 

 Z was less was always flatter, and lay completely below the 

 curve for which Z was greater. The greater is Z the greater 

 is the ionization caused in the platinum by rays with a speed 

 between W and 20 volts *. For curves A and B Z is 1*40 

 and 0'47 respectively. 



* It would probably have been better to measure V rather than Z ; 

 a small Z corresponds to a large V . But in some cases the value of 

 Y was inconveniently large. 



