493 



Using the same methods as described abov-e, the ionisation chamber (I) 

 is constructed. No mica windows are needed in the front door or the 

 back side of" (this ionisation) chamber. The dimensions of (I) are 12 x 12 x 

 12 cm., and the thickness of the walls is 1.7 mm. With the exception of the 



A 



Fig. 2. 



mica window the door to the ionisation chamber is constructed like that of 

 the door to the gold leaf box. The front door should be binged to the 

 box and the back side can either be permanently soldered to the box or it 

 can be fastened by means of hinges. 



The two boxes (E) and (I) are fastened together by screws, the right 

 hand sides being flush with each other as shown in Fig. 1. This arrange- 



