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

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VI. _Hyperbolam_ AEB, cujus _Centrum_ C, tangant duæ rectæ
BT
, ES, &
reliqua ponantur ut in proximè præcedente; erit T D:
11Fig. 137. A D & lt; SP. AP.
Nam eſt CA. CD: : CT. CA. unde CA - CT. CD -
CA
:
: CT. CA; hoceſt TA. AD: : CT. CA. ſuppare diſ-
curſu
, eſt SA.
AP: : CS. CA. Verùm eſt CT. CA & lt; CS.
CA. quare TA. AD & lt; SA. AP; ſeu componendo TD. AD
&
lt; SP. AP.
VII. _Circali_ AEB (cujus _Centrum_ C) & _paraboliformis_ AFB
communes
ſint axis AD, &
baſis BD; ſit autem _paraboliformis_ ex-
ponens
{_n_/_m_};
& AD = {_m_ - 2 _n_/_m_ - _n_} CA (vel _m_ - _n_. _m_ - 2 _n_: :
CA
.
AD) _circulum_ verò tangat recta BT; hæc quoque _paraboli-_
_formem_
AFB continget.
Nam quia BT _circulum_ tangit, eſt CT CA: : CA. CD; unde TA.
22Fig. 138.AD: :. CACD. componendóque TD. AD: : CA + CD. CD Item, quo-
uiam
eſt (ex hypotheſi) CA.
AD: : _m_ - _n_. _m_ -2 _n_; erit per ratio-
nis
converſionem CA.
CD: : _m_ - _n. n_. & componendo CA +
CD
.
CD: : _m. n_. hoc eſt TD. AD: : _m. n_. unde palàm 332 _hujus ap._ quòd BT _paraboliformem_ AFB tangit.
VIII. Subnotetur, quòd inversè, datâ ratione ipſius AD ad CA’
deſignabitur
hinc _paraboliformis_;
quæ _Circulum_ AEB ad B contin-
get
.
Nempe, ſi AD = {_s_/_t_}, erit {_t_ - _s_/2 _t_ - _s_} dictæ _paraboliformis ex-_
ponens
.
Nam poſito fore {_t_ - _s_/2 _t_ - _s_} = {_n_/_m_}; erit ideò (juxta crucem
multiplicando
) _mt_ - _ms_ = 2 _tn_ - _sn_;
& tranſponendo _mt_ -
2
_nt_ = _ms_ - _ns_.
ac ideò (æqualitatem ad analogiſmum redigendo)
_m_
- _n.
m_ - 2 _n_: : _t. s_: : CA. AD. itaque conſtat ex anteceden-
te
Propoſitum.
IX. Manente quoad cætera ſeptimæ hypotheſi, _paraboliformis_
AFB
extra _circulum_ AEB tota cadet.
Nam utcunque ducatur recta GEF ad DB parallela; quæ ſecet
44Fig. 139. circulum ad E, paraboliformem in F;
ductæque concipiantur rectæ
ES
_circulum_, &
recta FR _paraboliformem_ contingentes;

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