1G4 Mr Glazebrook, On some equations connected with [Nov. 28, 



The magnetic forces are 



4nrVS, kF^, WV'S', 

 and the magnetic displacements 



4>7Tfx,VS, 4 i TrfiV 1 S v lir/SV'S'. 

 Take the electric conditions first. 

 Resolving, we have for electric displacements in direction A, 



S cos AP + S t cos AP t = 8' cos AF (18). 



Electric forces in direction B, 



|Uos BP + j* cos BP x =*ja cos BF (19). 



(Since the wave normal is at right angles to BB' the electric 

 force along the wave normal has no component in direction B.) 



In direction C, 



~ cos GP - |i cos G'P l = ~ cos CP' + JL tan % cos NG . . . (20). 



Magnetic displacement in direction A, 



/iVS cos AQ + /iV&cos AQ X = ft' V'& cos AQ' (21). 



Magnetic force in direction B, 



VScosB'Q+V&cosBQ^V'S' cosB'Q' (22). 



In direction C, 



VScos CQ- V& cos C'Q X = V'S' cos GQ (23). 



Also Z =/ * F2 ' Z 7 = /i ' F ' 2 ' 



V V V. 



- — r — - — T7 = • , = p, say, 

 sin <p sm (f> sin <j) 1 r J 



cos AP = sin 9 sin = V cos BQ 



= V sin 6 = p sin 6 sin <£. 



Thus (18) and (22) reduce to 



8 sin 6 sin <£ 4 /S^ sin a sin (^ = S' sin 0' sin $'. 



Again -^ cos jBP = fiV* cos = ju,p* sin 2 <£ cos 0, 



/xFcos AQ = /iFcos sin <p 

 = fxp sin 2 cos 6, 



