292 



Prof. R. R. Sarrni on the 



Fig. 2 (a) "represents the gas-chamber. It is made of 

 metal with the left end open. The rim o£ this end is pro- 

 vided with a carefully ground flange, so that the slate G can 

 easily be fixed on to it air-tight with a little grease, as shown 

 in the diagram. At the other end, the chamber has a tube C 

 also of metal passing through the lid as seen in the figure. 



Fig. 2. 



(a} 



zzzzzzzzzzzzzzzzz 



U zz7Z7777>y;.v;yrp7r.'TT 



C FJ C" 



i 



h I 



iE_viZ:2Zl2I 



1 2 3 4- 5- 



i i 1 -i-~ 1 J 



centimetres. 



The tube C has two small holes, one at each end, 2-3 mm 

 in diameter. The hole at the outer end is closed by means 

 of a thin sheet of mica, the stopping-power of which is equi- 

 valent to about 1*5 cm. of air. This forms a small mica 

 window W through which the active particles are shot into 

 the chamber from a source placed next to the mica. The 

 hole at the inner end of C is covered by a small piece of 

 platinum foil with a fine pin-hole F in the centre of it. In 

 addition, there are three or four larger holes in the sides of 

 the tube C as shown at h, h. These are provided to facilitate 

 the exhaustion of the whole chamber CC, and to prevent 

 too much pressure being exerted during the process on the 

 platinum foil. The distance FW = FP — 3 cm, Itis necessary 



