﻿Emission of Electrons by X-Rays. 



705 





Fig. 1 shows the final form of the apparatus used. Kays 

 from an X-ray tube enclosed in a thick lead box passed 

 through a small aperture in the box and entered the 

 cylindrical brass examination vessel A through a hemi- 

 spherical glass window W. Inside the vessel, in the path 

 of the rays, was suspended an insulated brass cube (J, which 

 served to carry the materials to be examined. In order that 

 more than one substance might be investigated without dis- 

 mantling the apparatus, the cube was made capable of 

 rotation about a vertical axis by means of a ground-glass 

 joint G, which carried the whole of the insulated system. 



Fio-. 1. 



By turning this joint through 90° at a time different 

 materials could be exposed to the action of the rays. The 

 beam of X-rays was such that the cross-section was never as 

 large as the area of the material under examination, so that 

 only the window and the matter on the face of the cube were 

 exposed to direct X-ray bombardment. An electromagnet M 

 was arranged near the window so that any electrons from 

 the window might be bent back into the walls of the vessel 

 and thus prevented from reaching the cube. The inside of 

 the vessel was lined with filter paper to reduce the effect of 

 the scattered and characteristic radiations from the cube. 

 Inside the vessel and insulated from it was placed a wide- 

 meshed wire cylinder which could be charged to any desired 

 potential. 



3 F 2 



