﻿of Ions made by a, ft, 7, and X Rays. 211 



The swinging needle was allowed to settle down in a few 

 cases, and its deflexion compared with that calculated by- 

 means of the above formula from two swings : the ao-reement 



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was very good. The value of ^ . calculated from observa- 

 tions of K, was found to be '65 when either the lead or 

 aluminium chamber was in connexion with the electrometer. 



The deflexion proper (a? ), when the adjustable chamber 

 was connected with the electrometer, was also calculated by 

 means of this formula. 



The deflexions of the electrometer-needle were obtained 

 from the motion of the image of a scale across the cross-wire 

 of a telescope, a scale being placed in such a position that an 

 image of it was reflected into the telescope by the mirror of 

 the electrometer-needle. 



Besides the experiments with X rays, a set of experiments 

 was carried out with the a rays of uranium. The contrast 

 which appears in the behaviour of these two different ionizing 

 agents will, I think, be brought out better if these experi- 

 ments are described before any of the actual observations 

 made with X rays are given. The apparatus used in these 

 experiments consisted of a square flat metal box (see fig. 2), 



Fi<r. 2. 



19 cms. by 19 cms., and 1*5 cm. high. The electrode con- 

 nected with the electrometer was a thick lead plate, 18 cms. 

 by 18 cms., suspended from insulating supports. The case was 

 connected with the high potential. A plate, covered with a 

 very thin layer of uranium oxide, could be slid in from one 

 side. The distance between the layer of uranium oxide and 

 the lead plate was *5 cm. 



The following table gives some of the readings taken. The 

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leak w r as allowed to run into the electrometer for 13 seconds, 

 the connexion between chamber and electrometer was then 

 broken and the first and second swing of needle read. The 

 deflexion proper ( t r ) was calculated by the formula given, 



the value of ■ , Tr having been found to be '61. 

 1 + K n 



The natural leak of chamber and electrometer (when the 



