Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/368

 No: For the point would be changed, and would be beneath the star first observed.

You are in the right. Now like as that which in this example answereth to the elevation of the Top-Gallant-Top, is not the star, but the point of the Firmament that lyeth in a right line with the eye, and the said top of the Mast, so in the case exemplified, that which in the Firmament answers to the Pole of the Earth, is not a star, or other fixed thing in the Firmament; but is that point in which the Axis of the Earth continued streight out, till it cometh thither doth determine, which point is not fixed, but obeyeth the mutations that the Pole of the Earth doth make. And therefore Tycho, or who ever else that did alledg this objection, ought to have said that upon that same motion of the Earth, were it true, one might observe some difference in the elevation and depression (not of the Pole, but) of some fixed star toward that part which answereth to our Pole.

I already very well understand the mistake by them committed; but yet therefore (which to me seems very great) of the argument brought on the contrary is not lessened, supposing relation to be had to the variation of the stars, and not of the Pole; for if the moving of the Ship but 60. miles, make a fixed star rise to me one degree, shall I not find alike, yea and very much greater mutation, if the Ship should sail towards the said star for so much space as is the Diameter of the Grand Orb, which you affirm to be double the distance that is between the Earth and Sun?

Herein Simplicius, there is another fallacy, which, truth is, you understand, but do not upon the sudden think of the same, but I will try to bring it to your remembrance: Tell me therefore; if when after you have directed the Quadrant to a fixed star, and found v. g. its elevation to be 40. degrees, you should without stirring from the place, incline the side of the Quadrant, so as that the star might remain elevated above that direction, would you thereupon say that the star had acquired greater elevation?

Certainly no: For the mutation was made in the Instrument and not in the Observer, that did change place, moving towards the same.

But if you sail or walk along the surface of the Terrestrial Globe, will you say that there is no alteration made in the said Quadrant, but that the same elevation is still retained in respect of the Heavens, so long as you your self do not incline it, but let it stand at its first constitution?

Give me leave to think of it. I would say without more ado, that it would not retain the same, in regard the pro-