Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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ſtanding of which, I ought firſt to advertiſe you, that when ever
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the new Star, or other Phænomenon is near to the earth, turning
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with a Diurnal motion about the Pole, it will ſeem to be farther
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off from the ſaid Pole, whilſt it is in the lower part of the
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an, then whilſt it is above, as in this Figure [
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being fig. </
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<
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>third of
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this Dial.
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] may be ſeen. </
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<
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>In which the point T. denotes the
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tre of the Earth; O the place of the Obſervator; the Arch VPC
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the Firmament; P. the Pole. </
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<
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>The
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Phænomenon,
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[
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or appearance
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]
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moving along the Circle F S. is ſeen one while under the Pole by
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the Ray O F C. and another while above, according to the Ray
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O S D. ſo that the places ſeen in the Firmament are D. and C. but
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the true places in reſpect of the Centre T, are B, and A,
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ſtant from the Pole. </
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<
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>Where it is manifeſt that the apparent place
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of the
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Phænomenon
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S, that is the point D, is nearer to the Pole than
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the other apparent place C, ſeen along the Line or Ray O F C,
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which is the firſt thing to be noted. </
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<
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>In the ſecond place you muſt
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note that the exces of the apparent inferiour diſtance from the Pole,
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over and above the apparent ſuperiour diſtance from the ſaid Pole,
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is greater than the Inferiour Parallax of the
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Phænomenon,
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that is, I
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ſay, that the exceſſe of the Arch C P, (the apparent inferior
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ſtance) over and above the Arch P D, (the apparent ſuperior
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ſtance) is greater then the Arch C A, (that is the inferiour
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lax.) Which is eaſily proved; for the Arch C P. more exceedeth
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P D, then P B; P B, being bigger than P D, but P B. is equal to
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P A, and the exceſſe of C P, above P A, is the arch, C A,
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fore the exceſſe of the arch C P above the arch P D, is
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er than the arch C A, which is the parallax of the Phænomenon
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placed in F, which was to be demonſtrated. </
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<
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>And to give all
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vantages to the Author, let us ſuppoſe that the parallax of the ſtar
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in F, is the whole exceſſe of the arch C P (that is of the inferiour
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diſtance from the pole) above the arch P D (the inferiour
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ſtance.) I proceed in the next place to examine that which the
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obſervations of all Aſtronomers cited by the Authour giveth us,
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amongſt which, there is not one that maketh not againſt himſelf
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and his purpoſe. </
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<
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>And let us begin with theſe of
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Buſchius,
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who
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findeth the ſtars diſtance from the pole, when it was ſuperiour, to be
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28
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gr. </
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<
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>10 m.
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and the inferiour to be 28
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gr. </
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<
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>30 m.
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ſo that the
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ceſſe is 0
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gr. </
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<
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>20 m.
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which let us take (in favour of the Author) as
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if it all were the parallax of the ſtar in F, that is the angle T F O.
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<
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>Then the diſtance from the
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Vertex
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[or Zenith] that is the arch
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C V, is 67
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gr. </
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<
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>20 m.
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Theſe two things being found, prolong the
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line C O, and from it let fall the perpendicular T I, and let us
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conſider the triangle T O I, of which the angle I is right angle,
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and the angle I O T known, as being vertical to the angle V O C,
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the diſtance of the ſtar from the
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Vertex,
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Moreover in the triangle </
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