4tf ) m { £*#* 



tur. Vnde patet , ipfum punctum fummum A in infinittim 

 finiftrorfum remoueri ; initium ergo huius curuae erit B, vbi 

 tanecns B D cft verticalis — —-. 



$• 9- Quod fi iani pro hac curua loco d s fcribamus 



V dx*-\-dy\ aequatio prodit x V dx 7 -\- dy r ~~- dx~b d\ 

 pofi to ~ = b , ita vt b exhibcat longitudinem fili protrafti; 

 vndc deducitur dy ~ d ^ V b b — x x, quac aequatio, pofit» 



V b b — x x — z , vt fit xxzzzbb-zz et 1* — — z d z 

 abit in hanc: </j — - ^^ - </s - 6 4^ergomtegrau- 

 do y — z — \ b l ?-~ confcquenter 



yzzzC-^-V bb-xx-\ bl b f^=^ . 



j -» t> — \ bb — xx. 



Vnde patct, fumto x — c, fbre y ~ C -f- b l oo, vnde intci- 

 ligitur, punchim A finiftrorfum in infinitum elongari. 



§. 10. Combincmus iam iftas duas hypothcfes ita, vt 

 forfitan ad vciitatem fatis prope acccdamus; pofito nimirum 

 angulo incidcntiac — (J), ft.atuam.us impulfionem vcnti propor- 

 tionalcm cfTc huic formulae : ( i — a) fin. Cp ! -f- a fm. Cj), vbi a 

 fit fracho fatis parua. Hinc cnim , quando angulus Cj) parum 

 a rcclo discrcpat, vt fit fin. Cj) — i, haec formula dabit i. Sin 

 autcm angulus Cj) fucrit valde paruus , vt fin. (J)' quafi euanes- 

 cat prac fin. Cj), impulfio fcquetur rationem fimplicem a fin. (J). 

 Quarc cum noftro cafu fit fin. <$> — t* , vis a vento orta crit 



'(-Ui ( * - *) ki -+- 4i- ) = - v d \ > >P^ P° flto £r - - « » 



aequatio noftra erit ~- z~ ( i — a j ~- -\- a d x , idcoquc 

 *—— ~ ( i — a) d x* -\- a d x d s, quac polito r/ s ~ r d x abit 

 in hanc: '-— ;i-a + ar. vnde deducitur .v — »«( , ' — «-*-« £j 

 Quare ctim f\t s zzzfr d x ~ r x —fx d r , hiuc habebiimis 

 J x d r zz - 2 ( i - a) a - -\- » a a l r , ficque ablcilfi v defini- 

 tur pcr nouam variabilem r, per quam etiam arcus s ita expri- 

 mitur, vt fit .c ~ 2 a a -+- *-^~ — } — z a xl r. 

 Acla Acad. Jmp. SY. To///. /. P. /. B b §. 1 1. 



