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Euclid: Elementa

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Click to Expand/Collapse OptionTitle
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POSTULATES. 
PETITIONES, SIVE POSTULATA 
求作四則
求作者。不得言不可作。 
1. Let the following be postulated: To draw a straight line from any point to any point. 
I. POSTVLETVR, vt à quouis puncto in quoduis punctum, rectam lineam ducere concedatur.
PRIMVM hoc postulatum planum admodum est, sirectè considerentur ea, quæ paulo ante de linea scripsimus. Nam cum linea sis fluxus quidam puncti imaginarius, atque adeo linea recta fluxus directo omnino itinere progrediens, fit vt sipunctum quodptam ad aliud directo moueri intellexerimus, ducta sane sit à puncto ad punctum recta linea: Id quod prima hac petitione postulat Euclides, quemadmodum hic vides à puncto A, ductamesse rectam lineam ad punctum B; ab eodemque aliam ad punctum C; Item aliam ad punctum D; & sic innumere aliæ ab eodem puncto educi possunt ad alia atque aliæ puncta. 
第一求
自此點至彼點。求作一直線。
此求亦出上篇。蓋自此點直行至彼點。卽是直線。
自甲至乙或至丙、至丁。俱可作直線。 
2. To produce a finite straight line continuously in a straight line. 
II. ET rectam lineam terminatam in continuum recta producere.
QVOD sipunctum illud ferri adhuc cogitauerimus motu directo, & qui omnis inclinationis sit expers, producta erit ipsa recta linea terminata, & nunquam erit finis huius productionis, cum punctum illud intelligere possimus moueri ad infinitam distantiam. Sic lines recta A B, producta est primo in continuum ad punctum C. Deinde ad punctum D, &c. 
第二求
(p. 一四)一有界直線。求從彼界直行引長之。
如甲乙線。從乙引至丙。或引至丁。俱一直行。 
3. To describe a circle with any centre and distance. 
III. ITEM quouis centro, & interuallo circulum describere.
IAM vero, si terminatam rectam lineam cuiuscunque quantitatis mente conceperimus applicatam esse secundum alterum extremũ ad quoduis punctum, ipsamque circa hoc punctum fixum circumduci, donec ad eum reuertatur locum, à quo dimoueri cœpit; descriptus erit circulus, essectumqúe, quod tertia petitio iubet. Exemplum habes in his quinque lineis A B, A C. A D, A E, A F, quæ singulæ citra centrum A, circumulutæ singulos circulos descripserunt iuxta quantitatem, seu interuallum ipsarum.
PRÆTER hæc tria postulata, quibus Euclides contentus fuit, sunt multa alia æquè facilia, è quibus duntaxat in medium proferre decreui illud, quod frequentius repetendum erit in progressu totius Geometriæ. Reliqua enim prudens lector ex se vel facilè intelliget.
 
第三求
不論大小。以點為心求作一圜。 
4. That all right angles are equal to one another. 
IV. ITEM quacunque magnitudine data, sumi posse aliam magnitudinem vel maiorem, vel minorem.
OMNIS enim quantitas continua per additionem augeri, per diuisionem vero diminui potest infinitè: Vnde nunquam dabitur quantitas continua adeo magna, quin ea maior dari possit: neque tam parua, quin minor ea possit exhiberi. Hoc idem in numeris verum est, quod ad additionem pertinet. Nam quilibet numerus per continuam additionem vnitatis augeri potest infinitè: quamuis in eius diminutione ad vnitatem indiuiduam deueniatur. 1  
第四求
(p. 一五)
設一度於此。求作彼度。較此度或大或小。凡言度者。或線或面。或體皆是。或言較小作大可作。較大作小不可作。何者。小之至極。數窮盡故也。此說非是。凡度與數不同。數者。可以長。不可以短。長數無窮。短數有限。如百數減半成五十。減之又減。至一而止。一以下不可損矣。自百以上。增之可至無窮。故曰可長不可短也。度者。可以長。亦可以短。長者增之可至無窮。短者減之亦復無盡。嘗見莊子稱一尺之棰。日取其半。萬世不竭。亦此理也。何者。自有而分。不免為有。若減之可盡。是有化為無也。有化為無。猶可言也。令已分者更復合之。合之又合。仍為尺棰。是始合之初。兩無能幷為一有也。兩無能幷為一有。不可言也 
5. That, if a straight line falling on two straight lines make the interior angles on the same side less than two right angles, the two straight lines, if produced indefinitely, meet on that side on which are the angles less than the two right angles. 
 
 
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