330 DE PRES^IONE FVNIVM 



vae dr follicifabitur fecunduTi dircdionem A X vi 

 ::z Q> d X — ^ d y ^ quain in thcoria generali voca» 

 ■vimus P^Ji tuin vero fecundu.n dncdionem X Y 

 vi ::i&dy-\-lldXf quae lupra crat y^d s. Hinc 

 igitur erit 

 /?ds—fedx-rndj tt fQJs—fQdy+fHdx, 



§. y. Quoniam igitur hic toram curuam ia 

 eodem plano fitam concpimus, pro ftatu aequiiibrii 

 vnicam habebimus aequationem 



Idyf dx - fdy fUdy -fd xf dy ^fdxfW dx zz o. 

 Tum vcro quia ipfam tenfionem in Y \t datam 

 fpu(ftamus — r , erit 



T--''f^^ifed X -fUdj) -p^^(fQdy-\-rndx 

 Vnde fumtis differentiahous pofitoque dy—pdXy 



vt fit d s~dxV i -{- p p hae duae aequationes fe- 

 quentes induent formas : 



p{redx^fTl(iy)—fQdy-\-r\ldx et 



T = -7T=(/0'^-V-/'n<//)- ,-7^-( iQdy^rUdx) 



in qua fi ex priore loco fH d x-\- fQ dj fubiU- 

 tuatur valor p( fQ dx -fU dy) prodibit 



T =: - V 7+ p p (fQ dx-rn dy ), 

 Diffi^Tentictur prior aequatio, fietque 

 df ( / 0^A- -/ ndy)-{-p(Q dx -Udy)-Qdy-{-IL dx 

 iiuc 



dp(rQdx-fnd)')-n{ i ^pp)dx 

 ideoquc 



/Qdx-fndy-L-^-J^U dx 



<juc 



