ELECTRIC DISCHARGE IN A V\( IIM 1 r 



The two ends, marked + and , of a tube from which nearly all air has been exhausted 

 are connected to electric terminals, thus producing an electric discharge in the vacuum tube. 

 This discharge travels straight along the tube, as in the upper diagram. When a magnetic 

 field is applied, however, the rays are deflected, as shown in the lower diagram. The similar- 

 ity of the behaviour of the electric discharge with the radium rays (see diagram of deflec- 

 tion of radium rays, post) shows that the two phenomena may be identified. It was by 

 this means that the characteristics of electrons were first discovered. 



THE RELATIVE SIZES OF ATOMS AND ELECTRONS 



