200 



22 



metal vessel of the same shape, 22 cm. high and 13 cm. in diameter, and provided 

 with two tubes (/) through which the gases to be examined are introduced. The 

 ionisation vessel and the inner cylinder (k) are concentrical and together form a 

 condenser. 



When in use, the electroscope, the inner cylinder and the testing vessel are 

 iirmly connected by means of screw threads, but under transport these three parts 

 of the apparatus are detached ; a brass cover is then screwed on to the bottom of 

 the electroscope in order to protect the lower surface of the amber against moisture 

 and dust. A distinctive feature of this testing apparatus is the adjustment of the 



neck of the vessel into which 

 the electroscope is screwed. The 

 ebonite ring (/) ;i) establishes a 

 firm connection between the 

 brass ring (r r) and the lid of 

 the vessel. For this purpose the 

 lid is fitted with a raised rim, 

 which fits hermetically into the 

 ebonite ring. The electroscope 

 is attached to the testing vessel 

 by means of a worm on the 

 inner side of the brass ring (r r). 

 The distance between the brass 

 ring and the rim (s s) is about 

 ^/s mm., so that the electroscope 

 vessel is insulated from the 

 ionisation chamber. A thin india- 

 rubber ring is placed between 

 the outside of the brass ring 

 and the electroscope in order 

 to make the connection between 

 the electroscope and the ionisa- 

 tion chamber airtight. 

 The electroscope vessel and the ionisation chamber, when connected, form 

 the outside of a perfectly closed condenser (a Faraday case). The inside of the 

 condenser is represented by the aluminium leaf, the rod (g) and the cylinder (/c). 

 But when the connection is broken, we have in the electroscope vessel and the 

 ionisation chamber two separate closed condensers of which the inner surfaces are 

 in connection with each other. 



Such a system of condensers establishes the theory that the fluctuations in 

 the charge of the inner system of conductors is proportionate to the changes 

 in the potential difference between the two outer conductors, provided that the 



R 



Fig. 



