Mr Wilson, On the Magnetic Deflection of Cathode Rays. 179 



Note on the Magnetic Deflection of Cathode Rays. By Harold 

 A. Wilson, D.Sc, M.Sc, B.A., Trinity College, Clerk Maxwell 

 Student. 



[Read 6 May 1901.] 



The experiments described in this note were undertaken with 

 the object of proving, more completely than has hitherto been 

 done, that the ratio of the charge carried by a cathode ray particle 

 or corpuscle to its mass is independent of the nature of the metal 

 of which the cathode is composed. 



It was shown by Prof. J. J. Thomson 1 that this ratio is the 

 same for cathodes of aluminium and iron and by W. Kaufmann 2 

 that it is the same for cathodes of aluminium and copper so that it 

 is the same with aluminium, iron and copper cathodes. 



In view of the great interest attaching to Prof. Thomson's 

 corpuscular theory it seemed to be worth while to prove experi- 

 mentally that the ratio in question is the same for a larger number 

 of metals having a greater range of properties than the above 

 three. 



The method I have used is similar to that employed by Kauf- 

 mann (loc. cit.). A narrow beam of the rays is deflected by the 

 magnetic field produced by a coil carrying a constant current and 

 the deflection and the potential difference used to produce the 

 rays are measured. 



If C is the current in the coil, V the potential difference em- 

 ployed and d the deflection of the end of the beam of rays, then 



d- — 

 ~ vT' 



where A is a constant which for a particular apparatus is propor- 

 tional to a / — , e and m being the charge and mass respectively of 

 a cathode ray particle. This formula was found by Kaufmann to 



1 Phil. Mag. [5] xliv., Oct. 1897. 



2 Wied. Ann. 61, pp. 544—552, 1897. 



VOL. XL PT. III. 14 



