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

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[Item 1.]
[2.] Imprimatur,
[3.] LECTIONES _OPTICÆ & GEOMETRICÆ:_ In quibus PHÆNOMENωN OPTICORUM Genuinæ _Rationes_ inveſtigantur, ac exponuntur: ET _Generalia_ Curvarum Linearum _Symptomata declarantur_. Auctore Isaaco Barrow, Collegii _S S. Trinitatis_ in Academia _Cantab._ Præfecto, Et _SOCIETATIS REGIÆ_ Sodale.
[4.] LONDINI, Typis _Guilielmi Godbid_, & proſtant venales apud _Robertum Scott_, in vico Little-Britain. 1674.
[5.] SPECTATISSIMIS VIRIS Roberto Raworth & Thomæ Buck ARMIGERIS;
[6.] Iſaac Barrow
[7.] Epistola ad LECTOREM.
[8.] Epiſtola; in qua Operis hujus Argumen-tum, & ſcopus brevitèr exponuntur.
[9.] Lect. I.
[10.] Lect. II.
[11.] Lect. III.
[12.] _Corol_. 1. Ang. _a_ BG. ang. _a_ BP > ang. δ BH. ang. δ BP. 2. Ang. _a_ BG. ang. PBG > ang. δ BH. PBH.
[13.] Lect. IV.
[14.] Lect.V.
[15.] Lect. VI.
[16.] Lect. VI I.
[17.] Lect. VIII.
[18.] Lect. IX.
[19.] Lect. X.
[20.] Lect. XIV.
[21.] Lect. XV.
[22.] APPENDICVLA.
[23.] Lect. XVI.
[24.] Lect. XVII.
[25.] Lect. XVIII.
[26.] ERRATA.
[27.] Benevolo Lectori.
[28.] Lectio I.
[29.] Lect. II.
[30.] Lect. III.
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6143 jam aliquoties inſinuatâ; ſcilicet ut ſit AB. YB : : √ Iq -Rq. I;
& deſignetur quilibet refractus KN; tum continuetur ratio YB ad
BN;
ut ſit ad has proportione quarta BP; & per punctum P du-
11Fig. 57, 58. catur recta PZ ad AB parallela;
refracto KN occurrens in Z; dico
nullum alium refractum per Z traſire.
Nam ſi ſieri poteſt tranſeat
alius ZR;
& per Y traducantur rectæ NYG, RYS ; è præmon-
ſtratis apparet quòd ſit RS = NG.
item è prædictis manifeſtum 2212. Lect. 4. quò RS & gt; N G. quæ repugnant.
339 hujus Lect.
XVI. Non diſpari ratione, quoad caſum ſecundum, deſignetur quilibet
refractus KN;
& fiat KB . GB : : √ Rq - Iq. R; tum adnexâ
GN, ad ipſas NG, GB ſumatur tertia proportionalis V;
& ſiat
NG.
V : : BN. NP; & per punctum P ducatur PY ad BA pa-
rallela refractum NK decuſſans in Z;
dico nullum alium refractum
per ipſum Z meare.
Nam, ſi neges, tranſeat alius ZR; & per
Y trajiciatur RY S;
& quoniam ZP . YP : : KB. GB : : √ Rq
- Iq.
R. ex * antedictis apparet fore RS = NG. quinetiam ob
44* 14. Lect.4. NGq .
GBq : : NG. V : : BN . NP . erit dividendo NBq.
GBq : : BP . NP . hoc eſt NPq. PYq : : BP . NP; inde facile
deducitur eſſe BP quartam proportionalem in ratione YP ad PN ;

conſequentérque fore RS minimâ NG majorem .
quod adver-
ſatur oſtenſis .
itaque potiùs per Z nullus alius tranſit reſractus:
Q.
E. D.
XV I. Prætereà, ſi refractum NKZ interſecet alius quilibet M I,
ad rectiorem pertinens incidentem (hoc eſt ut incidentiæ punctum M
inter B, &
N jaceat) interſectio X ſolitario puncto Z citerior erit
(ſeu perpendiculari KB propinquior) .
Nam ab X demittatur per-
55Fig. 59, 60. pendicularis XQ.
ipſam NG ſecans in γ ; & (in primo caſu) per
M, Y traducatur recta MY H.
ergò MH = Nγ. quare minima earum
quæ per Y angulo XQF interſeri poſſuntinter puncta M, N cadet
(utì nuper admonitum, &
adſtructum). puta ad φ. ergò quum ſit
BP quarta proportionalis in ratione YB ad BN ;
& BQ quarta
proportionalis in ratione YB ad B φ, erit PB &
gt; QB; adeóque
recta XQ rectis ZP, KB interjacet :
Q. E . D.
In ſecundo caſu, per γ trajiciatur recta M γ H. ergò cùm ſit
Q X.
Q γ : : PZ. PY : : √ Rq - Iq. R. erit HM = GN. ergò
minima per γ ducibilium angulo AB F intercipienda punctis M, N
intercider;
puta ad φ. quare QB quarta proportionalis erit in ratione
γ Qad Q φ;
& eſt γ Q. Qφ & gt; (γ Q. QN.) : : YP. PN . &

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