522 WBBER ON THE MEASUREMENT 



tion as the velocity — u, i. e. backwards, and this velocity during 

 the element of time dt would alter by — dii. 



The thii'd mass + a' e' would move with the velocity + u' in 

 the direction of the element «', which with the right lines drawn 

 from a to a', and produced, forms the angle 0. This velocity 

 in the element of time dt would alter by + du'. Moreover, 

 this electric mass would itself share the motion of the element a', 

 which takes place with the velocity ?; in a direction which forms 

 the angle rj with the prolonged right line drawn from « to «', and 

 is contained in a plane lying in this right line, which with the 

 plane running parallel with the element « through the same right 

 line, encloses the angle y. The velocity v would alter during 

 the element of time dthydv. 



The /onrth mass — «'e' would move, in accordance with the 

 determinations for a galvanic current, in the direction of the 

 element a', with the velocity — u', which during the element of 

 time dt alters hy — du' ; but, moreover, like the previous mass, 

 would itself acquire the velocity v of the element «' in the direc- 

 tion already indicated. 



The distances of the two former masses from the two latter, 

 at the moment under consideration, are equal to the distance r 

 of the two elements themselves ; but since they do not remain 

 the same, they may be denoted by r^, r^, r^, r^. 



Lastly, if two planes pass through the right line drawn from 

 a to a', the one parallel to a, the other to «', w would denote the 

 angle enclosed by these tM'o planes. 



Then, on applying the new principle, we obtain as the sum of 

 the forces which act upon the positive and negative electricity in 

 the element «', i.e. as the force which moves the element «' itself, 

 the following expression : — 



■^ aa ue.c^e' f (dr^ drl_ _ drl_ _ dr^ \ 

 • 16 • rr Wdt^ '^ df^ df^ dt"^ ) 



/ddr^ ddr^ _ ddr^ _ ddr\ \ 

 ~ VdW^ IT^ TT ~dt^)J' 



But for the difference of these forces, upon which the induction 

 depends, we have the following expression : — 



__ aa ae.u'b' f (dr^ _ dr^ dr^ _ dr^\ 

 16' rr \\di''' dt' ■*" dt^ df^J 



/ddr^ ddr^ ddr^^ ddr/\\ 



