432 Professor J. J. Thomson on Cathode Bays. [April 30, 



Thus, if there are N particles entering the cylinder each with a 

 charge e, and Q is the charge inside the cylinder, 



Ne=Q. 

 The kinetic energy of these 



4Nm«;2 = W 



where W is the mechanical equivalent of the heat given to the 



thermal junction. By measuring the curvature of the rays for a 



magnetic field, we get 



m 



— v=l. 



e 



Thus 



e ~ 2 W * 



In an experiment made at a very low pressure, when the rays 

 were kept on for about one second, the charge was sufficient to raise 

 a capacity of 1'5 microfarads to a potential of 16 volts. Thus 



Q = 2-4 X 10-^ 



The temperature of the thermo junction, whose thermal capacity 

 was • 005 was raised 3 • 3° C. by the impact of the rays, thus 



W = 3-3 X 0-005 X 4-2 X W 

 = 6-3 X 10^ 



The value of I was 280, thus 



^ = 1-6X 10-^ 

 e 



This is very small compared with the value 10"'' for the ratio of 

 the mass of an atom of hydrogen to the charge carried by it. If 

 the result stood by itself we might think that it was probable that 

 e was greater than the atomic charge of atom rather than that m 

 was less than the mass of a hydrogen atom. Taken, however, in 

 conjunction with Lenard's results for the absorption of the cathode 

 rays, these numbers seem to favour the hypothesis that the carriers 

 of the charges are smaller than the atoms of hydrogen. 



It is interesting to notice that the value of e/m, which we have 

 found from the cathode rays, is of the same order as the value lO'""^ 

 deduced by Zeeman from his experiments on the effect of a magnetic 

 field on the period of the sodium light. 



[J.J.T.] 



