218 Mr. W. Wilson on the Effect of Pressure on 



internal diameter is 10 inches, the height 16 inches, and the 

 thickness of the walls 1*5 inch. This is surrounded by an 

 iron water-jacket about *5 inch thick. A massive lid which 

 is made gas-tight by means of a lead joint can be fastened 

 down to the main body by screws S S which are 10 in number. 

 A rod K which projects into the chamber can be moved up 

 and doAvn by an insulated screw, and is itself insulated from 

 the rest of the apparatus by mica. The air is prevented from 

 escaping along the surface of the rod by means of a stuffing- 

 box. The leak of the air from the vessel was quite small, 

 not amounting to more than *5 atmosphere per hour at 

 40 atmospheres, and even this could be largely stopped by 

 tightening the stuffing-box. 



The electroscope used consisted of an aluminium vessel, 

 10 cms. cube, with a base of brass. Aluminium was used 

 because it has been found by other observers that the natural 

 ionization in vessels made from it is small. It rested on a 

 wooden stand securely fixed to the bottom of the pressure- 



Fisr. 2 



TOK 



chamber. A vertical section of the electroscope is shown in 

 fig. 2. The brass -base contained a central hole 1 cm. in 



