PEOCEEDINGS 



OF THE 



Camfeitnje f^jriki^jjJHral jjtonjeig. 



On the motion of a charged ion in a magnetic field. By 

 Professor J. J. Thomson. 



[Received January 23, 1899. Read Januaxy 23, 1899.] 



The motion of a charged particle when under the influence of 

 a magnet has hitherto been chiefly considered when, as in the 

 case of the cathode rays, the free path of the charged particle is 

 so long that the effects of its collision with the molecules of the 

 gas through which it moves are not appreciable. When, however, 

 the free path is small and the collisions numerous the effect of 

 the surrounding gas is to make the velocity of the particle pro- 

 portional to the force acting upon it; when the free path is long it 

 is the acceleration and not the velocity which is proportional to 

 this force. In the following paper I have investigated the effect 

 of a magnet on the motion of a charged particle when the free 

 path is small. 



Let X, Y, Z be the components of the electric intensity, 

 a, /8, 7 those of the magnetic force, u, v, w those of the velocity, 



vol. x. PT. II. 4 



