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

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309116 ta recta BD; curvam verò tangat recta BT; ſitque BP rectæ BD
particula
indefinitè parva;
ducatúrque recta POad DTparallela,
11Fig. 174. curvam ſecans ad N;
dico PNad NOrationem habere majorem quâ-
vis
deſignabili, puta quàm R ad S.
Nam ſit DE. ET: : RS; connexaque recta BEcurvam ſecet in
G
, rectam POin K;
per G verò ducatur FHad DAparallela.
quoniam igitur BP ponitur indefinitè parva, eſt BP & lt; BF; adeóq;
PK
&
lt; PN (nam ſubtenſa BGintra curvam tota cadit). ergo PN.
NO
&
gt; PK. KO: : DE. ET: : R. S.
IV. Hinc, ſi baſis DBin partes ſecetur indeſinitè multas ad puncta
Z
;
& per hæc ducantur rectæ ad DAparallelæ curvam ſecantes pun-
ctis
E, F, G;
per hæc verò ducantur _Tangentes_ BQ, ER, FS, GT
parallelis
ZE, ZF, ZG, DA occurrentes punctis Q, R, S, T;
habebit recta ADad omnes interceptas EQ, FR, GS, AT(ſi-
mul
ſumptas) rationem quàvis aſſignabili majorem.
Nam ducantur rectæ EY, FX, GV ad BD parallelæ. Habent
igitur
rectæ ZE, YF, XG, VA ad rectas EQ, FR, GS, AT (ſin-
22Fig. 175. gulæ ad ſingulas ſibi in directum poſitas reſpectivè) rationem deſigna-
bili
quâcunque majorem.
ergò ſimul omnes iſtæ ad has ſimul omnes
_rationem_
habent deſignabili quâvis _majorem;_
hoc eſt recta AD ad EQ
+ FR + GS + AT ejuſmodi rationem habet.
V. Hinc inter computandum, omnes EQ, FR, GS, AT ſimul ac-
ceptæ
nihilo æquivalent;
ſeu rectæ ZE, ZQ; & ZF, YR, & c. æ-
quantur
;
item tangentium particulæ BQ, ER, & c. reſpectivis _curvœ_
portiunculis
BE, EF, &
c. pares, & quaſi coincidentes haberi poſſunt.
quin & adſumere tutò licet, quæ evidentèr his cohærent.
VI. Sit porrò _curva_ quævis AB, cujus _Axis_ AD, & ad hunc
33Fig. 176. applicata DB;
æquiſecetur autem DB in partes indefinitè multas ad
puncta
Z, per quæ ducantur rectæ ad AD parallelæ, curvam AB
interſecantes
punctis X;
quibus occurrant per ipſa X ductæ ad BD
parallelæ
rectæ ME, NF, OG, PH;
ſit autem ſegmento ADB
(rectis AD, DB, &
curvâ AB comprehenſo) _circumſcripta ſigura_
ADBMXNXOXPXRA
major _ſpatio_ quodam S;
dico _ſegmentum_
ADB
non eſſe minus quàm S.
Nam ſi ſieripoteſt ſit ADB minus quàm S exceſſu _rectangulaum_
ADLKadæquante
, &
quoniam AReſt indefinitè parva, adeóque
minor
quàm AK, liquet rectangulum ADZRminus eſſe

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