Barrow, Isaac, Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur

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26774 M x TP: : RP. SP; & connectatur SF; hæc curvam
FBF tanget;
id quod omnino ſimili diſcurſu demonſtratur, quo ter-
tia hujus;
tantùm hîc (non per E ad VD parallela ducitur, at) con-
nectitur ET;
& loco ſeptimæ allegatur octava ſeptimæ Lectionis.
quid plura?
XIII. Adnotetur, ſi linea EBE ſit recta, (rectæ nempe BR coin-
cidens) eſſe lineam FBF ex _infinitis hyperbolis_ (vel _hyperboliformi-_
_bus_) aliquam;
quarum igitur (unà cùm aliarum infinities diverſi ge-
neris plurium) _Tangentes_ determinandi modum uno _Tbeoremate_ com-
plexi ſumus.
XIV. Quòd ſi puncta T, R non ad eaſdem partes puncti D (vel P)
cadant;
curvæ FBF tangens (BS) deſignatur faciendo N x RD-:
11Fig. 102. M \\ - N} x TD. M x TD: : RD. SD.
Simili planè diſcurſu conſtat hoc, tantùm (quartæ loco) ſeptimæ
Lectionis quintam adhibendo.
XV. Hinc autem nedum _Ellipſoidum_ omnium (poſito nempe line-
am EBE rectam eſſe, lineæ BR coincidentem) aſt aliarum alterius
generis _linearnm innumer abilium Taxgentes_ unâ operâ determinan-
tur.
_Exemplum._ Si PF ſit è quatuor mediis quarta, ſeu M = 5; & N
= 4;
erit SD = {5 TD x RD/4 RD - TD. }
_Notetur_; Si contigerit eſſe ND x RD = M/- N} x TD, eſſe DS
infinitam;
ſeu BS ipſi VD parallelam. Alia poſſent adnotari; ſed
relinquo.
XVI. Inter alias curvas innumeras, etiam hâc methodo _Ciſſois_ &
_Ciſſoidaliam_ omne genus comprehenditur:
Sit utique ſemirectus an-
22Fig. 103. gulus DSB;
curvæque duæ SGB, SEE ſic ad ſe referantur, ut
ductâ liberè rectâ GE ad BD parallelâ, (quæ lineas expoſitas, ut
conſpicis, ſecet) ſint PG, PF, PE continuè proportionales;
tangat
autem recta GT curvam SGB in G, reperietur quæ ad E lineam SEB
tangit, faciendo 2 TP - SP.
TP: : SP. RP; utique connexa
RE curvam SEE tanget.
Id quod è præmiſſis facilè colligitur.
Quòd ſi jam curva SGB ſit circulus, & applicationis angulus

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