Salusbury, Thomas
,
Mathematical collections and translations (Tome I)
,
1667
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<
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>SALV. </
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<
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>I ſee that you underſtand the buſineſſe very well. </
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<
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>I
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lieve that you do likewiſe comprehend, that, in regard the ſtar B
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is lower than C, the angle which is made by the rayes of the
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ſight, which departing from the two places A and E, meet in C,
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to wit, this angle A C E, is more narrow, or if we will ſay more
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acute than the angle conſtituted in B, by the rayes A B and
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E
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B.
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<
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>SIMP. </
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<
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>This I likewiſe underſtand very well.</
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<
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>And alſo, the Earth beine very little and almoſt
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ſible, in reſpect of the Firmament
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(or Starry Sphere
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;) and
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ſequently the ſpace A E, paced on the Earth, being very ſmall in
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compariſon of the immenſe length of the lines E G and E F,
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ſing from the Earth unto the Firmament, you thereby collect that
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the ſtar C might riſe and aſcend ſo much and ſo much above the
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Earth, that the angle therein made by the rayes which depart
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from the ſaid ſtationary points A and E, might become moſt
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cute, and as it were abſolutely null and inſenſible.</
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<
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>SIMP. </
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<
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>And this alſo is moſt manifeſt to ſenſe.</
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<
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>SALV. </
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<
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>Now you know
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Simplicius
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that Aſtronomers and
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thematicians have found infallible rules by way of Geometry and
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Arithmetick, to be able by help of the quantity of theſe angles
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B
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and C, and of their differences, with the additional knowledg
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of the diſtance of the two places A and E, to find to a foot the
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remoteneſſe of ſublime bodies; provided alwayes that the
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ſaid diſtance, and angles be exactly taken.</
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<
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>SIMP. </
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<
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>So that if the Rules dependent on
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Geometry
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and
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nomy
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be true, all the fallacies and errours that might be met with
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in attempting to inveſtigate thoſe altitudes of new Stars or
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mets, or other things muſt of neceſſity depend on the diſtance A E,
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and on the angles B and C, not well meaſured. </
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<
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>And thus all thoſe
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differences which are found in theſe twelve workings depend, not
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on the deſects of the rules of the Calculations, but on the errours
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committed in finding out thoſe angles, and thoſe diſtances, by means
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of the Inſtrumental Obſervations.</
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<
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>SALV. True; and of this there is no doubt to be made. </
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<
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>Now
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it is neceſſary that you obſerve intenſely, how in removing the Star
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from B to C, whereupon the angle alwayes grows more acute, the
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ray E B G goeth farther and farther off from the ray A B D in
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the part beneath the angle, as you may ſee in the line E C F,
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whoſe inferiour part E C is more remote from the part A C, than
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is the part E B, but it can never happen, that by any whatſoever
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immenſe receſſion, the lines A D and E F ſhould totally ſever from
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each other, they being finally to go and conjoyn in the Star: and
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onely this may be ſaid, that they would ſeparate, and reduce
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ſelves to parallels, if ſo be the receſſion ſhould be infinite, which </
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