292 ADVANCED ELECTRICITY AND MAGNETISM. 



collapse at a given instant sending out a 7-wave, an a-particle, 

 and a /3-particle. The relative positions reached by the 7-wave, 

 the a-particle, and the jS-particle at a given instant are shown 

 in the figure. The a-particle is a large positively charged particle 

 and the /3-particle is a small negatively charged particle. 



148. Determination of velocity and mass of the particles 

 which constitute canal rays (or a-rays) and cathode rays (or 

 j8-rays). A narrow stream of rays from a radio-active substance 

 may be obtained by the arrangement shown in Fig. 212 in which 



A photographic plate ff 



^radio-active 

 material 



Fig. 212. 



AB is a sensitive photographic plate upon which the narrow 

 stream of rays impinges. Figure 213 shows the effect of an 

 electrical field upon a thin stream of rays from a radio-active 

 substance. The direction of the electric field is shown by the 

 fine horizontal arrows (the lines of force of the electric field pass 

 from the positively charged plate to the negatively charged 

 plate). The effect of the electrical field is to deflect the a-par- 

 ticles in the direction of the field and the /3-particles in the oppo- 

 site direction, while the 7-rays are not deflected at all. The 

 amount of deflection in each case may be determined by develop- 

 ing the photographic plate upon which the rays impinge. The 

 effect of the magnetic field upon the rays from a radio-active 

 substance is shown in Fig. 214 in which the fine horizontal lines 



