Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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1downwards, and alſo forwards or backwards ten or fifteen fathom,
keeping it all the while parallel to its ſelf, the viſive ray cannot
ſtray from the point obſerved in the object, more than thoſe
teen fathom; and becauſe in a diſtance of eight or ten miles, the
Inſtrument takes in a much greater ſpace than the Gally or other
Veſſel kenn'd; therefore that ſmall mutation ſhall not make me
loſe ſight of her.
The impediment therefore, and the cauſe of
loſing the object cannot befall us, unleſſe upon the mutation made
angularly; ſince that Teleſcopes tranſportation higher or lower, to
the right, or to the left, by the agitation of the ſhip, cannot import
any great number of fathomes.
Now ſuppoſe that you had two
Teleſcopes fixed, one at the Partners cloſe by the Deck, and the
ther at the round top, nay at the main top, or main top-gallant
top, where you hang forth the Pennon or ſtreamer, and that they
be both directed to the Veſſel that is ten miles off, tell me,
ther you believe that any agitation of the ſhip, & inclination of the
Maſt, can make greater changes, as to the angle, in the higher tube,
than in the lower?
One wave ariſing, the prow will make the main
top give back fifteen or twenty fathom more than the foot of the
Maſt, and it ſhall carry the upper tube along with it ſo greata ſpace,
& the lower it may be not a palm; but the angle ſhall change in one
Inſtrument aſwell as in the other; and likewiſe a ſide-billow ſhall
bear the higher tube an hundred times as far to the Larboard or
Starboard, as it will the other below; but the angles change not at
all, or elſe alter both alike.
But the mutation to the right hand or
left, forwards or backwards, upwards or downwards, bringeth no
ſenſible impediment in the kenning of objects remote, though the
alteration of the angle maketh great change therein; Therefore it
muſt of neceſſity be confeſſed, that the uſe of the Teleſcope on the
round top is no more difficult than upon the Deck at the Partners;
ſeeing that the angular mutations are alike in both places.
SALV. How much circumſpection is there to be uſed in affirming
or denying a propoſition?
I ſay again, thar hearing it reſolutely
med, that there is a greater motion made on the Maſts top, than at
its partners, every one will perſwade himſelf, that the uſe of the
leſcope is much more difficult above than below.
And thus alſo I w
ill excuſe thoſe Philoſophers, who grow impatient and fly out into
paſſion againſt ſuch as will not grant them, that that Cannon bullet
which they cleerly ſee to fall in a right line perpendicularly, doth
abſolutely move in that manner; but will have its motion to be by
an arch, and alſo very much inclined and tranſverſal: but let us
leave them in theſe labyrinths, and let us hear the other objections,
that our Author in hand brings againſt Copernicus.
SIMP. The Author goeth on to demonſtrate that in the
ctrine of Copernicus, it is requiſite to deny the Senſes, and the

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