FACTORS OF A CORPUSCLE. 



57 



they undergo. The path of the corpuscles is made visible 

 by a special method to be afterward considered. 



This fact, namely, that a magnetic force will bend a beam of 

 corpuscles, solves our problem. It may be shown beyond all 

 question that when a magnet is presented at a stream of 

 corpuscles, each corpuscle tends to describe a circle at right 

 angles to the magnetic force, and, furthermore, that the 



Fig. 13. Showing raj^s deflected by horseshoe magnet. 



radius of this circle equals ^ where m is the mass of the 



corpuscle, v its velocity, e its electrical charge, and H the 

 amount of the magnetic force. Returning to the diagram 

 of the apparatus, you will find that it is possible to meas- 

 ure the radius of this circle of corpuscular motion ; for when 

 the magnetic force is just sufficient to deflect the corpuscles 

 wholly to the electrode, C, they travel from E to C along 



