RELATIONS TO OTHER SCIENCES 145 



are always identical with one another in all their properties, what- 

 ever may be the matter which has furnished them. We have already 

 seen how the direct measurement of the charge leads always to the 

 same result, The mass, both the longitudinal and transverse mass, 

 having the same value for small velocities, can be determined by the 

 measurement of the ratio of the charge to the mass. 



The results obtained for this ratio in the case of cathode rays 

 show some quite marked divergences when different methods of 

 measurement are employed. The first values were given by J. J. 

 Thomson by combining the magnetic deviation of the rays with a 

 . measurement of the energy which they possess by means of the heat 

 produced in a thermoelectric couple which receives them, or by 

 combining this magnetic deviation with the deviation in an electro- 

 static field. The ratio ^ furnished by this second method, the more 

 accurate of the two, is approximately 10 7 electromagnetic units 

 C.G.S. 



Another method first pointed out by Schuster was used successively 

 by Kaufmann and Simon. It consists in combining the magnetic 

 deviation with the measurement of the difference of potential under 

 which the rays are produced, considering that this difference of po- 

 tential is that which exists between the cathode and anode. This 

 hypothesis admitted, the method is capable of great accuracy, and 

 the results which it gives appear to agree with the limiting values, for 

 small velocities of the ratio ^ for the /? rays, although the method 

 employed by Kaufmann in this last measurement is different from 

 that of Schuster. The number obtained by Simon is 1.865X10 7 , 

 nearly double that of J. J. Thomson. The explanation proposed by 

 the latter for this disagreement, according to which the cathode 

 rays are not produced by the total difference of potential between the 

 cathode and the anode, but originate in a region situated in front of 

 the cathode, does not, however, appear satisfactory, since it does not 

 account for the constancy of the results of Kaufmann and Simon 

 when the conditions of the experiment, the difference of potential 

 in particular, were varied between large limits. 



A means of deciding the question would consist in performing a 

 type of experiment already used by Lenard, by subjecting the cathode 

 rays, after their production, to a supplementary and known fall of 

 potential, and determining by the modification which would result 

 in their magnetic deviation the initial fall of potential under which 

 they had been produced. 



(34) The Cathode Corpuscle. However it may be, we can, owing 

 to the results of Kaufmann, affirm the identity of the cathode rays 

 already found independent of the gas and the electrode contained 

 in the Crookes tube, with the /? rays of radium. The measurements 



