270 Mr. W. Sutherland on 



force mv 2 /p equal to H^v, and therefore our second equation 

 is 



vm/e=*Rp (2) 



By measuring W/Q and Hp, Thomson is able to deduce 

 values of v and m/e from (1) and (2), and these are the values 

 which lead to his remarkable conclusions already given. 



Thomson and Kaufmann control the results of this method 

 by a second method of experimenting, in which deflexion of 

 cathode rays was produced by electrostatic force, as well as 

 by magnetic, the forces in Thomson's experiments being 

 adjusted so that the deflexions in both cases were the same, 

 and therefore, if F is the electric force, 



Fe = Rev (3) 



Thus an independent measure of v is taken, and as it confirms 

 those made by the other method, the experimental evidence 

 for the simplicity of the laws of cathode motion is greatly 

 strengthened. But in the theory of these experiments there 

 is one suppressed premiss, namely, that a charge e must be 

 associated with some mass m. Now in following up the 

 ionic hypothesis as far as it w T ill go, it is our duty to use this 

 premiss as one of the links in the chain of reasoning ; but 

 when it leads us to a conclusion subversive of the ionic 

 hypothesis, namely, that atoms are split up into particles 

 having different charges from the atomic charge in electro- 

 lysis, then we are no longer bound by the ionic hypothesis. 

 It may therefore be that free electrons can appear in the 

 sether, and that in the cathode stream the greater part of the 

 electricity travels as free electrons. 



A systematic statement of the reasons for contemplating 

 the possibility of the motion of free electrons through the 

 gether will be given below ; but in the present connexion it 

 is of most importance to consider whether such electrons could 

 give up to the thermopile the kinetic energy measured by 

 Thomson. From the writings of Thomson, Heaviside, Searle, 

 and Morton (Phil. Mag. [5] xi., xxvii., xxviii., xli., xliv.) 

 we can form an idea as to what takes place when an electron 

 is set in motion. These writings relate to electric charges 

 .on conducting spheres and ellipsoids, the charges being 

 caused to move by the motion of the conductors; but in the 

 case of the free electron we cannot say that its charge is on 

 anything, unless a modified portion of the sether. Our 

 simplest plan is to regard the electron as a spherical shell of 

 electricity of total amount e, the radius being a. 



The main effect of setting such an electron in motion by 

 means of some source of energy, is that electric and magnetic 



