Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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[Figure 331]
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deſcribed within the ſame, and neerer to the pole A, ſhall wholly
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be included in the illuminated part; as on the contrary, the
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poſite ones towards the Pole B, contained within the
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lel L M, ſhall remain in the dark. </
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>Moreover, the arch A I
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ing equal to the arch F D, and the arch A F, common to them
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both, the two arches I K F and A F D ſhall be equal, and each
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a quadrant or 90 degrees. </
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>And becauſe the whole arch I F M
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is a ſemicircle, the arch F M ſhall be a quadrant, and equal to
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the other F K I; and therefore the Sun O ſhall be in this ſtate
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of the Earth vertical to one that ſtands in the point F. </
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>But by
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the revolution diurnal about the ſtanding Axis A B, all the points
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of the parallel E F paſſe by the ſame point F: and therefore in
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that ſame day the Sun, at noon, ſhall be vertical to all the
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bitants of the Parallel E F, and will ſeem to them to deſcribe in its
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apparent motion the circle which we call the Tropick of Cancer.
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>But to the inhabitants of all the Parallels that are above the
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rallel E F, towards the North pole A, the Sun declineth from
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their
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Vertex
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or Zenith towards the South; and on the contrary,
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to all the inhabitants of the Parallels that are beneath E F,
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wards the Equinoctial C D, and the South Pole B, the Meridian
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Sun is elevated beyond their
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Vertex
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towards the North Pole A.
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Next, it is viſible that of all the Parallels, only the greateſt C D
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is cut in equal parts by the Terminator of the light I M. </
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>But
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the reſt, that are beneath and above the ſaid grand circle, are all
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interſected in parts unequal: and of the ſuperiour ones, the
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midiurnal arches, namely thoſe of the part of the Terreſtrial
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face, illuſtrated by the Sun, are bigger than the ſeminocturnal
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ones that remain in the dark: and the contrary befalls in the
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remainder, that are under the great one C D, towards the pole B,
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of which the ſemidiurnal arches are leſſer than the ſeminocturnal,
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It is likewiſe apparently manifeſt, that the differences of the ſaid
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arches go augmenting, according as the Parallels are neerer to
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the Poles, till ſuch time as the parallel I K comes to be wholly in
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the part illuminated, and the inhabitants thereof have a day of
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twenty four hours long, without any night; and on the contrary,
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the Parallel L M, remaining all in obſcurity, hath a night of
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twenty four hours, without any day. </
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>Come we next to the
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third Figure of the Earth, placed with its centre in the point
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Cancer, where the Sun ſeemeth to be in the firſt point of
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pricorn. </
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>We have already ſeen very manifeſtly, that by reaſon
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the Axis A B doth not change inclination, but continueth
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lel to it ſelf, the aſpect and ſituation of the Earth is the ſame to
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an hair with that in the firſt Figure; ſave onely that that
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ſphere which in the firſt was illuminated by the Sun, in this
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maineth obtenebrated, and that cometh to be luminous, which in </
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