64 LEAKAGE IN ULTRA-VIOLET LIGHT [CH. vi. 



some residual air, interfering with the perfectly free 

 path of the moving bodies. Nevertheless it was sharp 

 enough for fair determination ; and the result was 

 again, in this case also, that the ratio e/m came out 

 10 7 c.g.s., or more exactly 7xl0 6 ; corresponding 

 closely with the values found by J. J. Thomson, 

 confirmed subsequently by both Lenard and Kauf- 

 mann, for the cathode ray particles. 



Another phenomenon on which measurements were 

 made w r as the discharge of negative electricity from 

 an incandescent carbon filament in an atmosphere of 

 rarified hydrogen. This also is subject to disturb- 

 ance by a magnetic field, as was shown by Elster and 

 Geitel ; and a series of measurements, on lines similar 

 to the preceding, resulted in a value 



- =87x 10 6 c.g.s., 

 m 



a value of the same order of magnitude as before : one 

 thousand times greater than the electrochemical or 

 electrolytic value for hydrogen, and many thousand 

 times greater than for other substances, but always 

 constant and independent of the nature of the sub- 

 stance present. 



Another method for measuring these quantities, in 

 what may seem a more direct manner, was devised 

 by Professor Lenard and is depicted in fig. 10. It 

 will be realised that the remarkable character of 

 these experiments is the fact that nothing is visible : 

 there are no cathode rays to be seen, nor any 

 phosphorescent spot produced ; all that can be 

 observed is either a maximum deflexion of the 

 electrometer, as by Lenard's plan, or a zero deflexion 

 suddenly changed to a finite deflexion, in J. J. 

 Thomson's plan. 



