Prof. J. J. Thomson on Cathode Rays. 307 



It will be noticed that the value of m/e is considerably 

 greater for Tube 3, where the opening is a small hole, than 

 for Tubes 1 and 2, where the opening is a slit of much greater 

 area. I am of opinion that the values of m/e got from Tubes 

 1 and 2 are too small, in consequence of the leakage from the 

 inner cylinder to the outer by the gas being rendered a con- 

 ductor by the passage of the cathode rays. 



It will be seen from these tables that the value of m/e is 

 independent of the nature of the gas. Thus, for the first tube 

 the mean for air is '40 X 10 — 7 , for hydrogen *42 X 10~ 7 , and 

 for carbonic acid gas *4x 10 — 7 ; for the second tube the mean 

 for air is "52 X 10 — 7 , for hydrogen *50 x 10~ 7 , and for carbonic 

 acid gas "54 X 10 -7 . 



Experiments were tried with electrodes made of iron instead 

 of aluminium; this altered the appearance of the discharge and 

 the value of v at the same pressure, the values of m/e were, 

 however, the same in the two tubes ; the effect produced by 

 different metals on the appearance of the discharge will be 

 described later on. 



In all the preceding experiments, the cathode rays were 

 first deflected from the cylinder by a magnet, and it was then 

 found that there was no deflexion either of the electrometer or 

 the galvanometer, so that the deflexions observed were 

 entirely due to the cathode rays ; when the glow mentioned 

 previously surrounded the cylinders there was a deflexion of 

 the electrometer even when the cathode rays were deflected 

 from the cylinder. 



Before proceeding to discuss the results of these mea- 

 surements I shall describe another method of measuring 

 the quantities m/e and v of an entirely different kind from 

 the preceding; this method is based upon the deflexion of 

 the cathode rays in an electrostatic field. If we measure the 

 deflexion experienced by the rays when traversing a given 

 length under a uniform electric intensity, and the deflexion 

 of the rays when they traverse a given distance under a 

 uniform magnetic field, we can find the values of m/e and v in 

 the following way : — 



Let the space passed over by the rays under a uniform 

 electric intensity F be I, the time taken for the rays to 

 traverse this space is l/v, the velocity in the direction of F is 

 therefore 



Fe I 

 m v 

 <o that 0, the angle through which the rays are deflected 

 when they leave the electric field and enter a region free 

 from electric force, is given by the equation 



