Newton, Isaac, Philosophia naturalis principia mathematica, 1713

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                    <margin.target id="note469"/>
                  DE MUNDI
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                  SYSTEMATE</s>
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                  <s>Idem colligitur ex curvatura viæ Cometarum. </s>
                  <s>Pergunt hæc
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                    <arrow.to.target n="note470"/>
                  corpora propemodum in circulis maximis quamdiu moventur cele­
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                  rius; at in fine curſus, ubi motus apparentis pars illa quæ à pa­
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                  rallaxi oritur, majorem habet proportionem ad motum totum ap­
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                  parentem, deflectere ſolent ab his circulis, & quoties Terra mo­
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                  vetur in unam partem, abire in partem contrariam. </s>
                  <s>Oritur hæc
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                  deflexio maxime ex Parallaxi, propterea quod reſpondet motui
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                  Terræ; & inſignis ejus quantitas, meo computo, collocavit diſpa­
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                  rentes Cometas ſatis longe infra Jovem. </s>
                  <s>Unde conſequens eſt
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                  quod in Perigæis & Periheliis, ubi propius adſunt, deſcendunt
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                  ſæpius infra orbes Martis & inferiorum Planetarum. </s>
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                  <s>
                    <margin.target id="note470"/>
                  LIBER
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                  TERTIUS.</s>
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                  <s>Confirmatur etiam propinquitas Cometarum ex luce capitum. </s>
                  <s>
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                  Nam corporis cœleſtis a Sole illuſtrati & in regiones longinquas
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                  abeuntis, diminuitur ſplendor in quadruplicata ratione diſtantiæ:
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                  in duplicata ratione videlicet ob auctam corporis diſtantiam a
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                  Sole, & in alia duplicata ratione ob diminutam diametrum appa­
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                  rentem. </s>
                  <s>Unde ſi detur & lucis quantitas & apparens diameter
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                  Cometæ, dabitur diſtantia, dicendo quod diſtantia ſit ad diſtan­
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                  tiam Planetæ, in ratione diametri ad diametrum directe & ratione
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                  ſubduplicata lucis ad lucem inverſe. </s>
                  <s>Sic minima capillitii Co­
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                  metæ anni 1682 diameter, per Tubum opticum ſexdecim pedum
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                  a
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                  Flamſtedio
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                  obſervata & Micrometro menſurata, æquabat 2′. </s>
                  <s>0″. </s>
                  <s>
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                  Nucleus autem ſeu ſtella in medio capitis vix decimam partem la­
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                  titudinis hujus occupabat, adeoque lata erat tantum 11″ vel 12″. </s>
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                  Luce vero & claritate capitis ſuperabat caput Cometæ anni 1680,
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                  ſtellaſque primæ vel ſecundæ magnitudinis æmulabatur. </s>
                  <s>Ponamus
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                  Saturnum cum annulo ſuo quaſi quadruplo lucidiorem fuiſſe: &
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                  quoniam lux annuli propemodum æquabat lucem globi inter­
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                  medii, & diameter apparens globi ſit quaſi 21″, adeoque lux
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                  globi & annuli conjunctim æquaret lucem globi, cujus diameter
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                  eſſet 30″: erit diſtantia Cometæ ad diſtantiam Saturni ut 1 ad √ 4
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                  inverſe, & 12″ ad 30″ directe, id eſt, ut 24 ad 30 ſeu 4 ad 5.
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                  Rurſus Cometa anni 1665 menſe
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                  Aprili,
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                  ut author eſt
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                  Hevelius,
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                  claritate ſua pene Fixas omnes ſuperabat, quinetiam ipſum Satur­
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                  num, ratione coloris videlicet longe vividioris. </s>
                  <s>Quippe lucidior
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                  erat hic Cometa altero illo, qui in fine anni præcedentis apparu­
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                  erat & cum ſtellis primæ magnitudinis conferebatur. </s>
                  <s>Latitudo
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                  capillitii erat quaſi 6′, at nucleus cum Planetis ope Tubi optici
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                  collatus, plane minor erat Jove, & nunc minor corpore interme-</s>
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