152 CHEMICAL DISCOVERY AND INVENTION 



on either side are excited the phosphorescent patch is broadened 

 out on one side showing that the rays causing the fluorescence 

 have been deflected. 



By reversing the magnetic field the broadening of the fluor- 

 escent patch takes place in the opposite direction. The 

 deflection can also be shown by taking advantage of the 

 photographic properties of these rays. 



The /3-rays consist of particles (electrons, see p. 118) carrying 

 a negative charge. This can be ob- 

 served by means of an ingenious device 

 arranged by Strutt and called the 

 " radium clock." It consists of a glass 

 tube evacuated as completely as pos- 

 sible by means of a mercury pump, 

 and partially lined with tinfoil con- 

 nected with earth. In the vertical 

 axis of this vessel is suspended, by a 

 quartz rod, a small tube containing a 

 radium salt in metallic connection with 

 a pair of gold leaves attached to the 

 lower end by means of a brass cap. 

 The lower part of the tube containing 

 the radium is smeared with phosphoric 

 acid to render it conducting. While 

 the negative /3-rays are discharged into 

 the glass of the tube, the gold leaves 

 gradually acquire a positive charge, 

 which they retain, if the vacuum is 

 good, till they diverge sufficiently to 

 fo earth touch the tinfoil lining of the bulb, 

 when they instantly collapse. They 

 then gradually get recharged, and the 

 operation is repeated at intervals, the 

 frequency of which depends on the 

 amount and activity of the substance 

 connected with the gold leaves. (Philo- 

 sophical Magazine, 1903, p. 588.) 

 But the radiations of thorium and radium designated a, /3, 

 and y, are accompanied by an active substance which was found 

 to be carried off in a current of air, and which, though it would 

 pass slowly through paper, could be prevented from escaping 



FIG. 54. 

 STRUTT'S RADIUM CLOCK. 



