﻿of Ions made by a, j3, 7, and X Rays. 275 



identical construction, though somewhat smaller, and its lead 

 plate was connected with the mercury cup e. 



The X rays were generated by an X-ray bulb F, which 

 was enclosed, together with the induction-coil, in a lead box 

 having a window for the exit of the rays. When X raya 

 were allowed to fall on the two chambers, some of the rays 

 penetrated the aluminium plates, and meeting the lead plates 

 gave rise to an intense secondary radiation from the surface 

 of the lead, so that the air between the plates was principally 

 ionized by secondary X rays. The intensity of the primary 

 raya was cut down to the required amount by placing sheets 

 of tinfoil over the w T indow of the lead chamber in which the 

 X-ray bulb and induction-coil were enclosed. 



The primary X rays were investigated by means of two 

 chambers of the form EF. The electrodes of these chambers 

 consisted of brass rings over which tissue-paper had been 

 tightly stretched, and this covered with thin aluminium-leaf. 

 This arrangement introduced little secondary radiation. The 

 electrodes were at a distance of "5 cm. from one another. 

 The central electrode of the standard chamber was connected 

 with the mercury cup e, and that of the adjustable chamber 

 was connected with the mercury cup c. Each pair of outside 

 electrodes was connected with a battery. 



If na denote the leak per second in the adjustable chamber, 

 the leak in the standard chamber may be denoted by nb, and 

 the ratio of the leaks of the two chambers, when taken for a 



time t, is I — j- j, that is ( - ), a quantity independent of the 



time of leak and the variations in intensity of the rays. If 

 the leak in the adjustable chamber changes when a different 

 E.M.F. is applied, the change is proportional to a, that is to 



a , . . 



t , since is constant. 

 



It was found that if the electrodes of the two chamber 3 

 were not of exactly the same material, the compensation was 

 not perfect. This appeared to be due to the X rays varying 

 not only in intensity but also in nature, and their variations 

 in nature not giving rise to equal relative changes in the 

 intensity of the secondary radiations, on account of the 

 materials being different. 



The observations were carried out in the foilowino- 

 manner : — 



At the beginning of an observation the mercury cup d was 

 kept earthed, and each of the cups e and c kept connected 

 with d. The current was then started in the primary circuit 



T 2 



