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

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24350 _d_ = _m_; vel _dy_ - _xy_ = {_d_/_b_}_x x_. Aliaquædam hîc (nonnulla forſan παρέργως)
inſeremus.
XIII. Sit poſitione data recta ID; ſit item curva DNN talis,
11Fig. 46. utin ID ſumpto puncto quopiam G, ductâque rectâ GN ad poſitio-
nem datam IK parallelâ;
ſumptiſque determinatis lineis _g, m, r_;
poſitíſque DG = _x_, & GN = _y_; ſit perpetim _y x_ + _gx_ - _my_ =
{_m_/_r_}_x x_;
linea DNN erit _hyperbola_, ſic determinabilis: Sumatur
DM = _m_;
& per M ducatur ML ad IK parallela; & in hac acci-
piatur MQ = {_mm_/_r_};
& ſit QY = MQ; & ab MY auferatur
YZ = _g_;
connexâque QD, ducatur ZT ad QD parallelâ; erunt
ZM, ZT _aſymptoti_.
Nam ducatur ZS ad MD parallela; cui occurrat GN producta in
R (ſed &
GR ipſam ZT ſecet in P). Eſtque jam PN = RG -
RP - GN = {_mm_/_r_} - _g_ + {_mx_/_r_} - _y_.
adeoque PN x MG = {_m_3/_r_}
- _mg_ + _yx_ + _gx_ - _my_ - {_m_/_r_}_x x_ = {_m_3/_r_} - _mg_ + _o_.
= {_m_3/_r_}
- _mg_ = DM x ZQ.
unde PN. ZQ: : (DM. MG: :) QD.
ZP. ergo PN x ZP = ZQ x QD. Liquetigitur curvam DNN
eſſe _hyperbolam_, cujus _aſymptoti_ ZM, ZT.
Siæquatiò ſit - _yz_ + _gx_ + _my_ = {_m_/_r_} _xx_; eadem erit _hyper-_
_bola_.
Sed puncta G inter B, M tunc accipiuntur; & ità prout aliis
ac aliis locis puncta G deſignantur, æquationis ſigna variantur;
at
non eſt ea jam exponendi locus.
XIV. Poſitione datæ ſint rectæ DB, BA; pérque rectam DB
feratur recta CX ad BA parallela;
item per punctum D rotando
22Fig. 47. tranſeat recta DY, ſic ipſam BA ſecans in E, ut ſit inter rectas BE,
DC eadem ſemper proportio (puta quæ cujuſdam aſſignatæ R ad DB)
rectæ verò DE, CX ſe interſecent punctis N;
erit linea DNN _Pa-_
_rabola_.
Nam ſit R. DB: : DB. P. Eſt ergò BE. DC: : DB. P. Item
eſt DB.
BE: : DC. CN. ergò DB. BE + BE. DC = DC.

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