﻿788 Dr. Norman Campbell on 



Fig:* 3 merely shows the part of the curve for small values 

 of Y on a scale larger than that of fig. 2. The continuous 

 and dotted curves in fig. 2 (and the marks o and x, for 



Fi<r. 3. 



the corresponding observations) refer respectively to the 

 results obtained with the induction-coil and the influence- 

 machine. Not all the observations are plotted, but those 

 which are given are thoroughly representative. 



Fig. 4. 



P 0-05 



O 



Q Q Q- 



^ * O 



* o 



It will be observed that there is some difference between 

 the observations with the influence-machine and those with 

 the induction-coil, the values of P for the latter being some- 

 what lower. The difference cannot be due to the coil giving 

 a " reverse current," for the presence of such a current 

 would decrease i 1 and increase i 2 (since cathode rays also 

 cause ionization) and so increase P. I am inclined to think 

 that the smaller values of P with the coil are due to a lack 

 of homogeneity of the positive rays and the presence of some 

 possessing energies considerably lower than the maximum 

 indicated by the spark-gap, a conclusion which is enforced by 

 the fact that the results were much more regular and con- 

 sistent when the influence-machine was used. In an attempt 

 to extend the observations with the machine to higher values 

 of Vj a serious accident to the apparatus occurred. Since the 



