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

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297104 AEG æquatur _Circulari ſegmento_ ADB demonſtrationem, ne longiùs
evager, obmittam.
XXXIV. Sint duo _circuli_ AIMG, AKNH ſeſe contingentes ad A;
11Fig. 154. communique diametro AHG, utcunque perpendicularis ducatur recta
DN M:
habebit_ſegmentum_ AIMD ad _ſegmentum_ AKND mino-
rem rationem, quam recta DM ad rectam DN.
Nam ſit AR ad AG perpendicularis, ac ipſi AH æqualis; &
connectatur HR, cui occurrat recta MD in X;
ducatúrque recta
GXS;
tum ad axem AG _parametrum_ AS per N deſcripta con-
cipiatur _Ellipſis_ ALNG;
hæc (utì ſatis manifeſtum) intra arcum
AKN tota cadet.
Eſt autem ſegm. AIMD. ſegm. ALND: :
DM.
DN. ergo ſegm. AI MD. ſegm. AKND & lt; DM. DN.
XXXV. Sit Ellipſis YFZT, cujus axes conjugati YZ, FT; ſit item
recta DC axi majori YZ parallela;
& per D, F, C tranſeat circulus
22Fig + 154. DFCV centrum habens K, in ellipſis axe minore FT ſitum;
dico
circuli partem DOFPC intra ellipſis partem DMFNC jacere.
Nam ſit FI ad FV perpendicularis, & in hac ſumatur FS = FV; &
connectatur VS, cui DC producta occurrat in X;
& connexa TX
ipſi FI occurat in R.
& cum ſit GDq = FG x GV = FG x GX;
liquet ipſam FR eſſe ellipſis, axi FT congruam, parametrum; unde
conſtat Propoſitum.
XXXVI. Sit circuli, cujus centrum L, ſegmentum DEC, & ſumpto
33Fig 155. in ejus axe GE puncto quopiam F, ſit curva DMFC talis, ut ductâ
utcunque rectâ RMS ad GE parallelâ, ſit RS.
RM: : GE. GF;
erit DMFC ellipſis, hoc modo determinata: Fiat EG. FG: : GL.
GH;
& per H erigatur YHZ ad DC parallela, ſitque HY par ipſi LE;
erunt HY, HF ellipſis ſemiaxes.
Demonſtratum habetur à _Greg. à S. Vincentio_, L. IV. Prop. 154.
_Corol._ Hinc ſegm. DEC. DMFC: : EG. FG.
XXXVII. Sint duæ circulorum portiones DEC, DOFC, quarum
communis ſubtenſa DC, &
axis GFE; portio major DEC ad portio-
nem DOFC majorem rationem habet eâ, quam habet axis GE ad
axem GF.
Nam ſint L circuli DSEC, & K circuli DOFC centra; & fiat EG.
FG: : GL. GH; & fiat YHZ ad HF perpendicularis & ſit HY æ-
qualis ipſi LE;
tum ſemiaxibus HY, HF deſcripta concipiatur ellipſis
YDMFCZ;
è mox prædictis liquet ellipſin DMFC circulo DOFC
circumduci.
Eſt autem circulare ſegmentum DEC ad ſegmentum el-
lipticum DMFC, ut GE ad GF;
quare ſegm DEC ad ſegm circula-
re DOFC.
rationem habet majorem, quàm GE ad GF: Quod. E. D.

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