763 



and higher orders c/\) = -f-) = 9(^1 = y(2) =0 if not a = i = 4. This 



■^ •^' ab ' ab •' ab ' ab 



involves, exact up to terms of the second order inclusive, 



when not ^ r ^ 4. In the latter case 



and 



For /> and </ we lind for the same reasons 



44 \ 



and 



Now, putting 



^,,(1) = — c';iandi7,/-')=-rV, 



and neglecting quantities of order 2 in ;/44 '',</44-i y,^^ , y,,-', c(i! 

 and c''^', we find 



, , .,4'^'öy,;-2) ö</„'.-^>dy„a) 



and so 







and in the case = r ^ 4 



dB dX du dE dk du 



.s —=inLx + |c^ — /^ , ^ -- =r I c;.Af* + fc:^ — 3/- . 



a,9// ÖAV. :< Ö*V^ d.«,^. «,3y. Öx=< ^ a Ö.P^ do!^ 



In consequence to all these considerations we get 



(o/, da \ 



/ 0/ oft dft d^ \ Ö;. df< 



\dx.:dx., dx^dx.,J a OXxOXx 



Now, if everywhere we replace 22 -^— - — bv A (/j/) — jiAX — - P.Afi, 

 we obtain 



