﻿380 Dr. Norman Campbell on the 



was completely saturated when U= — 20. The presence of 

 reflexion makes the absolute values obtained unreliable (it- 

 is due to this reflexion that the current is not saturated 

 when U = 0, and that some of the rays appear to have a 

 negative velocity), but it should not influence greatly 

 the comparison of curves taken after different treatments 

 of P. 



The following table shows the results for nickel in states 

 A, B, B'. V in all cases was 400, but it appeared, as was 

 expected, that so long as V was considerably greater than 

 20, the form of the curve was independent of V. The 

 results with other metals were similar in all respects. 



u .... 



. +20 



+ 15 



+10 



+s 



+6 



+4 



+ 2 



+ 1 







_2 



-10 



-20 



p (state A ) . 



. 



•021 



•065 



•090 



•121 



•215 



•358 



•483 



•708 



•915 



•992 



1-000 



Pi » B') . 



.. 



•021 



•075 



•no 



•159 



•250 



•417 



•570 



•732 



•928 



•991 



1000 



P( ,, B) . 



. 



•033 



•087 



•121 



•186 



•295 



•500 



•681 



•811 



•934 



•991 



1-000- 



These figures seem to indicate that, so far as there is any 

 change in the speed of the rays, the speed increases as the 

 ionization decreases — a conclusion which would be recon- 

 cilable with the view that the lower ionization is caused by a 

 difficulty in the emergence of the electrons, so that only 

 those with the greater speed emerge. But it must be 

 remembered that, since the discharge is passed between P 

 and B there may be a change in the reflecting power of B 

 when the ionization is decreased ; a decrease in the reflect- 

 ing power of B with a decrease of ionization might also 

 account for the apparent change in speed, for the number 

 of rays leaving P and failing to return would be increased. 

 The results which have been given show that the reflecting 

 power of P for slow electrons is diminished greatly by the 

 passage of a discharge, and since this change appears to be 

 independent of the direction in which the discharge passes, 

 it is probable that the reflecting power of B is actually 

 diminished by the treatment that causes the decrease in 

 ionization, and that the apparent change in the speed of the 

 electrons is to be traced to this cause. 



8. Some observations were made to determine whether the 

 power of the metal to reflect incident rays with speeds 

 greater than 40 volts was altered during the change from 

 state A to B or B' ; no such change is to be expected, for 

 such reflexion probably takes place, not at the actual surface 

 of the metal, but after the rays have passed through the 

 surface. It is not, however, easy to determine the reflecting 

 power for rays which are capable of producing ionization in 



