i54 



Est ant.em 

 ( (dxd'y-dyd^x)^ ( dx''(dyY-'2dxdxd^xdy-\-dy^(d'xy\ 

 {dzd^x - dxd^zy =x -+- dz^ (d^xf- 2 dxdzd^'x dH -+- dx^ {dH)A 

 {dyd^z - dzdyy) (~h dy^ {dH)^- 2 dydzdy dH~h dz- {dyYj 



qui valor, ob ds- z:^ dx^ -\- df^ -{- dz'^ hincque dz^ z:i. ds^ 



— dx^ — dy^ et posito ds constante 



dz — — Ç^dx — g dy, 

 ad sequentem reducitur 



dx^{dyy'-2dxdyd^xdy-hdy^(d^xY ■ ^ 



-^ds%d^xy-dx^{d''xy-dx^{d^xy-i-2dx^{d^xy+2dxdyd^xd-y\ 



-l -^-dx^{d=zyK 



l4- d/^ (d^zy r^ 2dxdyd^xdy -(- 2dy^ (dyy -h ds- {dyYi 



I ^dx-{dyy-dy^{dyy] 



_ UJs^ {(d^^xy-h (dyyj -+- dx^ (d^xy-^ 2dxdyd^xdy-i~ dy\dyy) 

 ~~ j ^ (c?x= ^ dy^) {d'zy ' S 



zn ds- ((d'xy -^ {dyy)-h{dxd^x-hdydyy-+-{dx^ -h dy^) {d'zy 



— ds^- {{d'xy -H {dyy)) -F dz^ {d'z:)^-+-(dx'-^dy') {dHy 



— ds^ ( (a'^x)2 ^ (c/^r)^ -f- (c/^z)^) ;, 

 atque ita habebfrur 



AAl V . i\ _ ^^-^- — - -~ -^^^^ ^ 



quae expressio,. ob radium carvedinis 



r . 



denuo in hanc abit : 



XXV. N =r — '^ ; 

 ubi signuriï — , viiu normalem, N secundiinï directiones c 



