﻿the ol jjarticles expelled from Radium and Actinium. 353 



There are two cases o£ the theory which must bo separately 

 considered : — 



Case 1, when the deflexion of the « particle in passing 



through the electric field is less than d, the distance 



between the plates, 

 Case 2, when the deflexion is greater than d. 



Fig. 3 a. 



o \ a 



C £ 



Case 1, 



Fig. 3 b. 

 a_b_J 



F* 



K 



8 



H 



\ 

 C L £ 



Case 2. 



Case 1. — We shall now consider the theory for the first 

 case. On entering the electric field at A, each ol particle 

 describes a parabolic path, and on emergence from the field 

 moves in a straight line, the direction of which is a tangent 

 to the parabolic path at the moment of emergence. The 

 distance between the plates (0*21 mm.) is so small compared 

 with the length AB (3*77 cms.), that we may assume without 

 sensible error that the electric field is everywhere normal to 

 the path of the rays. Suppose that the electric field is applied 

 in such a direction that the a particle is urged in the direction 

 of the plate AB. Some of the « particles, which before the 

 field was applied fell on the photographic plate, are now 



Phil. Mag. S. 6. Vol. 12. No. 70. Oct. 1906. 2 A 



