J!^ •> N r f t t '»■«1 



<// V(P' + Q* + R'), at vero vire:» normalis et tangentialis 

 Uis et ©rf^J reducuntur ad hanc vnicam: d s V [[V -\- Q')\ 

 neccfTe e(l vt fiat V(n- + 0') == >^( P"' "^ ^' + Q') ideoque 

 n' — P^ H- Q' -+- R= - 0% fuie 



II n ^ j^- - (P P -i- Q Q -I- R R) ^ X* - </ j'. 



§. 12. Supra autcm vidimu3 efle 

 Qds — ^dx^q^dy-^-^Kdz^ 

 vnde fit 



^rt^j' — PP^A-'-hQQ(/y-f-R Kdz' 



4- aP (^dxdy-^z^^dxdz-^-il^dydz, 



Tum vero loco d s' valorem fuum d x^ -^- d y^ -^- d z^ fub- 

 ftituendo erit 



r_|_(PP_|-QQ_|_RR)^.v' 

 (PP-hQQ-hRRW.f^r ]+ (PP-f- QQ-j-R R)^)'* 



^4-(PP-^QQ_|_RRj^S', 



vnde fi fubtrahatur O' d s\ remanebit 



nn^.rzr(QQ4-RR)^A:= + (PP + RR)^r + (PP+QQ)'^^* 

 - 2?(ldxdy- 2?Kdxdz-'2(lRdydz, 

 quac exprcflio maniftflo rcducitur ad fummam trium (e- 

 quentium quadratorum: 



nnds- - (Pdr - Qr/.v)'-f ((Idz - R dyY + (Rdx - Vd z]\ 



§. 13. Cum jgitur fupra inuenerimus 



?df 



