102 Prof. F. Slate on Electronic 



Rigid dynamics has used us to the couple, which affects- 

 rotational) energy but not momentum. Moment of momen- 

 tum there bridges the break; its factor (g>) appears in 

 kinetic energy also. Both (ay, uj can be employed to 

 standardize (the former at unit axial distance) . That 

 thought falls into lino with equations (9, 10, 11, 12), and 

 with several obtrusive analogies to symptoms of a hidden 

 spin about the axis of advance, which the electron's dynamics 

 reveals. 



The foregoing statements have been kept on general 

 ground (for any (t*i)), with a definite purpose of insisting 

 upon the probably unrealized range within which that is 

 feasible ; but we take up finally the electron for which 

 {v x = c). The dominant criterion on the physical side is 

 yielded by a predetermined (or available) electromagnetic 

 energy (M). The Einstein velocities have been brought 

 under similar control by considerations based on activity *. 

 The dynamical schemes will look towards devising a 

 momentum (Q ; ) reducible to consistency with (M) and its 

 time-rate, when associated with the actual working-speed 

 (r). The remark following equation (17) enlarges some- 

 what the limits of that consistency : but the points of 

 agreement to contrive and their companion conventions may 

 be put thus : 



A'=|(M)=VT'; Q'sm,*; T'=|(Q'); 2E' = »Q';] 



t" [~^/-in/\ , 1 *dm 2 ~\ dv 2 dm 2 j 



vl = - r (E )+ -t' 2 — r^ =m 2 r-r- -t v 2 — — . I 

 [_dt K J 2 dt J 2 dt dt J 



Adding an assumption about effective inertia (m 2 ) to our 

 knowledge of (v) fixes the other (mechanical) quantities - r 

 hence any attempted adjustment of this sort stands or falls 

 mainly on that as a cardinal choice. The last equation 

 enforces the need, where (m 2 ) is variable, of upholding the 

 distinction between (A') and power (dW/dt) which equations 

 (12) formulate. Turning first to Abraham's electron, we 

 shall illustrate how the plan outlined above can be adapted 

 to his original development. That assigns a leading place 

 to " electromagnetic mass," as we know ; also it proves to 

 conform to the present train of ideas, though as a whole 

 they are not made explicit in it. Particularly for that 

 reason, the comparison is prori table. 



* See (I.), p. 437 ; (II.), eq. (18), etc. 



