Salusbury, Thomas Mathematical collections and translations 1667

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154
from the piece; and the departing from the state of rest, cannot
be, unlesse the immobility of the Terrestrial Globe be presuppo­
sed, which is the conclusion of that was in dispute; Therefore,
I reply, that those who make the Earth moveable, answer, that
the piece, and the ball that is in it, partake of the same motion
with the Earth; nay that they have this together with her from
nature; and that therefore the ball departs in no other manner
from its quiescence, but conjoyned with its motion about the cen­
tre, the which by its projection upwards, is neither taken away,
nor hindered; and in this manner following, the universal motion
of the Earth towards the East, it alwayes keepeth perpendicular
over the said piece, as well in its rise as in its return. And the
same you see to ensue, in making the experiment in a ship with
a bullet shot upwards perpendicularly with a Crosse-bow, which
returneth to the same place whether the ship doth move, or stand
still.

An instance a­
gainst the diurnal
motion of the earth,
taken from the shot
of a Peece of Ordi­
nance perpendicu­
larly.

The answer to the
objection, shewing
the equivoke.

Another answer
to the same objecti­
on.

SAGR. This satisfieth very well to all; but because that I have
seen that Simplicius taketh pleasure with certain subtilties to
puzzle his companions, I will demand of him whether, suppo­
sing for this time that the Earth standeth still, and the piece ere­
cted upon it perpendicularly, directed to our Zenith, he do at all
question that to be the true perpendicular shot, and that the ball
in departing, and in its return is to go by the same right line,
still supposing all external and accidental impediments to be re­
moved?

SIMP. I understand that the matter ought to succeed exactly
in that manner.

SAGR. But if the piece were placed, not perpendicularly, but
inclining towards some place, what would the motion of the ball
be? Would it go haply, as in the other shot, by the perpendi­
cular line, and return again by the same?

SIMP. It would not so do; but issuing out of the piece, it
would pursue its motion by a right line which prolongeth the e­
rect perpendicularity of the concave cylinder of the piece, unlesse
so far as its own weight would make it decline from that erection
towards the Earth.

SAGR. So that the mounture of the cylinder is the regulator of
the motion of the ball, nor doth it, or would it move out of that
line, if its own gravity did not make it decline downwards. And

therefore placing the cylinder perpendicularly, and shooting the
ball upwards, it returneth by the same right line downwards; be­
cause the motion of the ball dependent on its gravity is down­
ward, by the same perpendicular. The journey therefore of the
ball out of the piece, continueth or prolongeth the rectitude or
perpendicularity of that small part of the said journey, which it
made within the said piece; is it not so?