Barrow, Isaac
,
Lectiones opticae & geometricae : in quibus phaenomenon opticorum genuinae rationes investigantur, ac exponuntur: et generalia curvarum linearum symptomata declarantur
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cinnè penes vos eſto judicium. </
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<
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xml:space
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">Non diffitebor autem aut penitus diſſi-
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mulabo non eſſe nihil quod his objici poſſit, & </
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<
s
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xml:space
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">dubitandi cauſam inji-
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cere. </
s
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<
s
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xml:space
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preserve
">Cur enim, percontetur aliquis, quando ſolum punctum B vet-
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ſus A renitatur, & </
s
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<
s
xml:id
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xml:space
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">totum lineæ BD quod ſupereſt partes appetat
<
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contrarias, non circa punctum quodpiam aliud in ipſa BD, puncto B
<
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propinquius, ut puta circa X, potiùs iſta gyratio concipiatur peragen-
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da? </
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>
<
s
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xml:space
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">Reſpondeo quàm breviſſimè (quonia@ incitato curſu tendens ul-
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">Fig. 6.</
note
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teriùs æ grè remoras fert) id in natura conſtanter accidere, quum mo-
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tus rectus in circularem degenerat, ut extremæ ſibimet adverſæ mobi-
<
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lium partes omnem motum dirigant ac moderentur, reliquis ad illa-
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rum ductum componentibus ſe, motúſque ſuos attemperantibus; </
s
>
<
s
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xml:space
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">ne-
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que non his quos ob extremarum contraniſmum, atque conflictum
<
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amittere neceſſe habent in illas transfundentibus; </
s
>
<
s
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xml:space
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">quo fit ut mediis
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hinc indè quàm tardiſſimè dimotis extremæ velociùs revolvantur, Ita-
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que cùm extrema puncta B, D partes in contrarium æquâ vi nitantur,
<
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neque niſi circa medium punctum Z rotatio peragatur, quod effectant
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aſſequi poſſint, id ſtatim fiet, & </
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<
s
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">reliquæ partes haud gravatim obſe-
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quentur. </
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<
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xml:space
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">Nè dicam in recta BD nullum aliud punctum exiſtere, cui
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præ aliis jure prærogativa competit, ut circa ipſum mobile libretur.
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</
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<
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xml:space
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">At pluribus abſtinens ad refractionis præcipuam legem haud abſimili
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diſcurſu proliciendam atque declarandam accedo. </
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<
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xml:space
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">Hanc nempe:</
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</
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<
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">IV. </
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">6. </
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<
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">Radii lucis alteri cuipiam diſſimili perſpicuo (nimirum ho-
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mogeneo quoad ſe) incidentes ità refringuntur, ut perpetuò recti ſi-
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nus inclinationum, quas habent incidentes, proportionales ſint rectis
<
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ſinubus inclinationum, quas obtinent refracti. </
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<
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">Huic elucidando, ſta-
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biliendóque decreto; </
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<
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xml:space
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">Parallelogrammum ABDC lucis radium re-
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præſentans impingat planæ ſuperficiei EF pellucidi medii (vel ſit recta
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EF ſectio communis, ut in caſu præcedente, quod & </
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>
<
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xml:space
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">abhinc ſemper
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intelligatur) progreſſum ejus aliquatenus retundentis. </
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>
<
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xml:space
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">Itaque medium
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iſthoc ſubingrediens punctum B procedere, tardiùs quidem, attenta-
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bit per rectam BG, ſeu peripſam AB protractam, intereà verò pun-
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ctum D in primo durans medio motum ſuum priorem adurgebit in re-
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cta CDH. </
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<
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xml:space
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">Hos autem conatus, aliàs irritos futuros (nec enim utrum-
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que poteſt rectum motum illud tardiùs, hoc velociùs incedendo conſer-
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vare) quàm proximè conſequentur, modò circa punctum aliquod in
<
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recta DB producta ſitum, puta quale Z, rotentur; </
s
>
<
s
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xml:space
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">ità ſcilicet ut dum
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punctum D in medio rariori (rarius appello quod minùs reſiſtit, aut
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retardat; </
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<
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">ut & </
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<
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">denſius quod motum magis reprimit, & </
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<
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">tardiorem
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reddit) velociùs latum deſcribit arcum majorem D δ; </
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