478 Hon. R. J. IStrutt on the /Aspersion of 



Probably a slight discharge from the kathode-point carries 

 heate d particles across to the other point, and a heated con- 

 dncting-path is thus formed, whereas no such projection 

 takes place at the other point, so that the spark-gap is not 

 heated by the flame and rendered conductive. 



It is well known that a flame influences the discharge 

 between points; but I know of no previous experiment by 

 which the entirely different effect of a flame on the different 

 poles is shown, when the circuit of the primary coil is inter- 

 rupted by an electrolytic break such as that of Wehnelt. 

 Oxford, September 22, 1899. 



LI. The Dispersion of the Cathode Rays hy Magnetic Force. 

 By the Hon. R. J. Strutt, B.A., Scholar of Trinity Col- 

 lege, Cambridge *. 



MBIRKELAND has observed that when a narrow 

 • beam of cathode rays (produced by an induction- 

 coil) is deflected by a magnetic field, some of the rays are 

 more deflected than others. The beam of rays falling on the 

 glass wall of the tube produces a narrow sharply-defined 

 phosphorescent line. When the rays are deflected by a 

 magnet this line is no longer single, but consists of a number 

 of bright bands with dark spaces between them. This 

 M. Birkeland calls the " magnetic spectrum." Now those 

 cathode particles which produce one of the bright bands must 

 differ in some way from those which produce another. Let 

 us suppose the magnetic field uniform, of intensity H, and at 

 right angles to the direction of the rays ; taking v as the 

 velocity, m as the mass, e as the electric charge of one of the 

 particles, r as the radius of curvature of its path when 

 deflected, then 



TT mv 2 mv 



i±ev= , or r= Tr -. 



r tie 



Since the deflexion, and consequently the value of r, varies 

 for the different bands, it follows that either the value of v 

 must be different for the various kinds of particles, or the 

 value of m/e must be different, or both these quantities must 

 vary. 



It seemed not impossible that there might really be several 

 kinds of particles with different values of m/e. If such a 

 conclusion could be established it would be of great interest. 



The other alternative would be that the values of v differ 

 for any two bands. Now it is scarcely possible to suppose 

 that particles of the same kind and of two different velocities 

 really are emitted simultaneously by a cathode, without sup- 

 posing that particles of intermediate velocities are emitted 



* Communicated by Lord Rayleigh, F.R.S. 



