﻿Ionization by Positive Rays. 



785 



phosphate or a mixture o£ sodium and aluminium phos- 

 phates, passed through the tube T with an energy cor- 

 responding to the difference of potential (V) between S and 

 A, and fell on the copper plate at the same potential as A. 



Fig. 1. 



L o 



The reflected rays and the electrons liberated at C fell on the 

 ■cylinder B and plate D, which were coated with soot to avoid 

 further reflexion. 



All the portion of the apparatus shown was enclosed in a 

 glass tube, covered with metallic foil to avoid electrostatic 

 disturbances and exhausted by connexion through a wide 

 tube to charcoal immersed in liquid air throughout the 

 observations. 



The values of V between and 400 volts were obtained 

 from cells ; no higher potential from this source was avail- 

 able. From 2000 volts upwards they were obtained either 

 from an influence-machine or an induction-coil. With the 

 machine, V was varied by varying a high resistance placed 

 as a shunt across its terminals ; with the coil, V was varied 

 by varying the current in the primary, a unidirectional 

 secondary current being secured by the use of the usual 

 valves. Y, when not greater than 400 volts, was read on a 

 voltmeter ; the higher values were determined by means of 

 i\ spark-gap between balls of 2 cm. diameter, the readings of 



Phil. May. S. 6. Vol. 29. No. 174. June 1915. 3 E 



