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

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1
Projects
nue their motion
by the right line
that followeth the
direction of the
gether with the
projicient, whil'ſt
they were conjoin'd
therewith.
SIMP. So it is, in my opinion.
SAGR. Now imagine the cylinder to be erected, and that the
Earth doth revolve about with a diurnal motion, carrying the
piece along with it, tell me what ſhall be the motion of the ball
within the cylinder, having given fire?
SIMP. It ſhall be a ſtreight and perpendicular motion, the
der being erected perpendicularly.
SAGR. Conſider well what you ſay: for I believe that it will
not be perpendicular.
It would indeed be perpendicular, if the
Earth ſtood ſtill, for ſo the ball would have no other motion but
that proceeding from the fire.
But in caſe the Earth turns round,

the ball that is in the piece, hath likewiſe a diurnal motion, ſo
that there being added to the ſame the impulſe of the fire, it
veth from the breech of the piece to the muzzle with two motions,
from the compoſition whereof it cometh to paſſe that the motion
made by the centre of the balls gravity is an inclining line.
And
for your clearer underſtanding the ſame, let the piece A C [in
Fig. 2.] be erected, and in it the ball B; it is manifeſt, that the
piece ſtanding immoveable, and fire being given to it, the ball
will make its way out by the mouth A, and with its centre,
ſing thorow the the piece, ſhall have deſcribed the perpendicular
line B A, and it ſhall purſue that rectitude when it is out of the
piece, moving toward the Zenith.
But in caſe the Earth ſhould
move round, and conſequently carry the piece along with it, in
the time that the ball driven out of the piece ſhall move along
the cylinder, the piece being carried by the Earth, ſhall paſſe
to the ſituation D E, and the ball B, in going off, would be at
the corniſh D, and the motion of the bals centre, would have
been according to the line B D, no longer perpendicular, but
clining towards the Eaſt; and the ball (as hath been concluded)
being to continue its motion through the air, according to the
direction of the motion made in the piece, the ſaid motion ſhall
continue on according to the inclination of the line B D, and ſo
ſhall no longer be perpendicular, but inclined towards the Eaſt,
to which part the piece doth alſo move; whereupon the ball may
follow the motion of the Eerth, and of the piece.
Now Simplicius,
you ſee it demonſtrated, that the Range which you took to be
perpendicular, is not ſo.
The revolution
of the Earth
poſed, the ball in
the piece erected
perpendicularly,
doth not move by a
perpendicular, but
an inclined line.
SIMP. I do not very well underſtand this buſineſs; do you,
Salviatus?
SALV. I apprehend it in part; but I have a certain kind of
ſcruple, which I wiſh I knew how to expreſs.
It ſeems to me, that
according to what hath been ſaid, if the Piece be erected
dicular, and the Earth do move, the ball would not be to fall, as
Ariſtotle and Tycho will have it, far from the Piece towards the