Homogeneous Corpuscular Radiation. 



341 



into the aperture B flush with the surface of the end plate. 

 A thin sheet of aluminium (*003 cm.) stretched as tightly as 

 possible was fastened over this aperture with Chatterton 

 compound. The pressure inside the ionization-chamber was 

 kept a little higher than atmospheric, and under these con- 

 ditions the aluminium window was as nearly as possible flush 

 with the plane of the end plate, even when the window was 

 only 1 mm. away from the plate R 2 and subject to its electro- 

 static attraction. The position of the inner sliding tube 

 relative to the outer case could be determined by means of a 

 millimetre scale engraved upon the surface of the inner tube, 

 while the outer casing carried a suitable vernier scale. The 

 diameter of the circular tertiary radiator was approximately 

 4*2 cm. The ionization-chamber was charged to a poten- 

 tial of +240 volts, a potential high enough to ensure a 

 saturation current from the case to the insulated plate in all 



Fisr. 2. 



Fiar. 3. 



ew volts. 



->/?&£ 



Earl 



cases. A portion of the secondary rays from the radiator \l l 

 passed through the window of E 2 , an electroscope of the 

 ordinary Wilson type. The ionization produced in this 

 electroscope served as a measure of the intensity of the 

 secondary beam. 



In figs. 2 and 3 are given views, in plan and elevation 

 respectively, of the various parts of the ionization-chamber I. 

 The wires leading from the radiator R 2 to the electroscope E :{ 

 were surrounded by earthed tubes. A key fitted to the 

 electroscope E 3 made it possible to earth or insulate the 

 radiator R 2 at will. When R 2 was earthed the 

 the electroscope E 3 to which it was connected 

 zero position, and this could be observed by 



gold-leaf 

 took 



of 

 up its 

 means of a 



microscope fitted with a scale in the eyepiece. On insulating 



