a'= — a 



520 Mr. E. Edser on the Reflexion of Electromagnetic 

 When = 0, (29) reduces to 



(c+ f = -a( e ± V \ 

 vr \c — vj- 



which agrees with (5). 

 From (23) and (27), 



v=\ 2A _ frf — *. .... (30) 



c 2 + ir + 2cv cos v y 



10. The instantaneous value of the pressure exerted on 

 each unit of area of the mirror, may be determined most 

 easily in terms of the force exerted on the screening current 

 induced on the surface of the mirror. Employing the method 

 used in § 6, we find that the tangential force exerted on a 

 unit N pole placed near the surface of the mirror, and 

 moving with it, is equal to 



^{(ccos 0-j-v) Et-(cos 0' — v)E 2 }, 

 c 



its positive direction being from South to North. The screen- 

 ing current C, flowing vertically upwards across unit breadth 

 of the mirror, is therefore given by 



C=~- 2 {(ccos0 + v)E v -(ccos0'-v)'E 2 }. . (31) 



The part of the tangential magnetic force which is not 

 derived from the current, and is independent of the velocity 

 of the mirror, is equal to 



^(Excostf-Escosfl') (32) 



The product of (32) and the value of C given in (31) will 

 give the instantaneous pressure p 1 at a point on the surface 

 of the mirror. From (31), (28), and (15), 



C=0(«cos0 + „); .... (33) 

 and 



(32) = | (cos 0- cos 6< 1) 



E i/ /i (c 2 + v 2 )cos0 + 2cv c 2 + v 2 + 2cv cos 0" 



1 COS0 + 



-BO 



c 2 + v 2 -f 2cv cos c 2 — v* 



_ ™ (c cos + v) 

 — Shi o o . 



c 2 — V 2 



2E 1 2 (ccos0 + v) 2 

 Pi- 



Attc 2 



