Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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compoſition of the two motions do go alwayes receding with
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greater and greater proportion from the circumference of that
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cle, which the centre of the ſtones gravity would have deſigned,
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if it had alwayes ſtaid upon the Tower; it followeth of neceſſity
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that this receſſion at the firſt be but little, yea very ſinall, yea,
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more, as ſmall as can be imagined, ſeeing that the deſcending
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grave body departing from reſt, that is, from the privation of
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motion, towards the bottom and entring into the right motion
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downwards, it muſt needs paſſe through all the degrees of
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ty, that are betwixt reſt, and any aſſigned velocity; the which
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degrees are infinite; as already hath been at large diſcourſed and
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proved.</
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>It being ſuppoſed therefore, that the progreſſe of the
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ration being after this manner, and it being moreover true, that
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the deſcending grave body goeth to terminate in the centre of the
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Earth, it is neceſſary that the line of its mixt motion be ſuch, that
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it go continually receding with greater and greater proportion
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from the top of the Tower, or to ſpeak more properly, from
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the circumference of the circle deſcribed by the top of the Tower,
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by means of the Earths converſion; but that ſuch receſſions be
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leſſer and leſſer
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in infinitum
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; by how much the moveable finds it
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ſelf to be leſſe and leſſe removed from the firſt term where it
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reſted. </
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<
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>Moreover it is neceſſary, that this line of the
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ed motion do go to terminate in the centre of the Earth. </
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>Now
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having preſuppoſed theſe two things, I come to deſcribe about
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the centre A [
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in Fig. </
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>1. of this ſecond Dialogue
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;] with the ſemi
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diameter A B, the circle B I, repreſenting to me the Terreſtrial
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Globe, and prolonging the ſemidiameter A B to C, I have
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ſcribed the height of the Tower B C; the which being carried
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about by the Earth along the circumference B I, deſcribeth with
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its top the arch C D: Dividing, in the next place, the line C A
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in the middle at E; upon the centre E, at the diſtance E C, I
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ſcribe the ſemicircle C I A: In which, I now affirm, that it is very
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probable that a ſtone falling from the top of the Tower C, doth
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move, with a motion mixt of the circular, which is in common,
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and of its peculiar right motion. </
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>If therefore in the circumference
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C D, certain equal parts C F, F G, G H, H L, be marked, and
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from the points F, G, H, L, right lines be drawn towards the
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centre A, the parts of them intercepted between the two
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cumferences C D and B I, ſhall repreſent unto us the ſame
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Tower C B, tranſported by the Terreſtrial Globe towards D I;
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in which lines the points where they come to be interſected by the
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arch of the ſemicircle C I, are the places by whichfrom time to
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time the falling ſtone doth paſſe; which points go continually
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with greater and greater proportion receding from the top of the </
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