CATHODE RAYS. 167 



be differently deflected from the single corpuscle; thus we should get 

 the magnetic spectrum. 



I have endeavored by the following method to get a measurement of 

 the ratio of the mass of these corpuscles to the charge carried by them. 

 A double cylinder with slits in it, such as that used in a former experi- 

 ment, was placed in front of a cathode which was curved so as to 

 focus to some extent the cathode rays on the slit; behind the slit, in 

 the inner cylinder, a thermal junction was placed which covered the 

 opening so that all the rays which entered the slit struck against the 

 junction, the junction got heated, and knowing the thermal caj)acity of 

 the junction, we could get the mechanical equivalent of the heat com- 

 municated to it. The deflection of the electrometer gave the charge 

 which entered the cylinder. Thus, if there are ]^ particles entering 

 the cylinder each with a charge e, and Q is the charge inside the cyl- 

 inder, 



The kinetic energy of these 



^ IST m -y^- = W 



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

 mal junction. By measuring the curvature of the rays for a magnetic 

 field we get 



Thus 



— V = 1. 





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 lO-'''. 



The temperature of the thermo junction, whose thermal capacity was 

 0-005 was raised 3*3° C. by the impact of the rays, thus 



W = 3-3 X 0-005 X 4-2 X 10^ 

 = 6-3x105. 



The value of I was 280, thus 



!^=l-6xl0-^. 



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 



