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 
, AC 
d = , 
flv 
where A is a constant which for a particular apparatus is propor- 
tional to /y/ — , 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. XI. PT. III. 
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