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

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1Weſt, nor as you would have it, upon the Piece, but rather far
diſtant towards the Eaſt.
For according to your explanation, it
would have two motions, the which would with one conſent carry
it thitherward, to wit, the common motion of the Earth, which
carrieth the Piece and the ball from C A towards E D; and the
fire which carrieth it by the inclined line B D, both motions
wards the Eaſt, and therefore they are ſuperiour to the motion of
the Earth.
SAGR. Not ſo, Sir. The motion which carrieth the ball
wards the Eaſt, cometh all from the Earth, and the fire hath no
part at all therein: the motion which mounteth the ball upwards,
is wholly of fire, wherewith the Earth hath nothing to do.
that it is ſo, if you give not fire, the ball will never go out of the
Piece, nor yet riſe upwards a hairs breadth; as alſo if you make
the Earth immoveable, and give fire, the ball without any
nation ſhall go perpendicularly upwards.
The ball therefore
ving two motions, one upwards, and the other in gyration, of both
which the tranſverſe line B D is compounded, the impulſe upward
is wholly of fire, the circular cometh wholly from the Earth, and
is equal to the Earths motion: and being equal to it, the ball
maintaineth it ſelf all the way directly over the mouth of the
Piece, and at laſt falleth back into the ſame: and becauſe it
ways obſerveth the erection of the Piece, it appeareth alſo
nually over the head of him that is near the Piece, and therefore
it appeareth to mount exactly perpendicular towards our Zenith,
or vertical point.
SIMP. I have yet one doubt more remaining, and it is, that in
regard the motion of the ball is very ſwift in the Piece, it ſeems
not poſſible, that in that moment of time the tranſpoſition of the
Piece from C A to A D ſhould confer ſuch an inclination upon
the tranſverſe line C D, that by means thereof, the ball when it
cometh afterwards into the air ſhould be able to follow the courſe
of the Earth.
SAGR. You err upon many accounts; and firſt, the inclination
of the tranſverſe line C D, I believe it is much greater than you
take it to be, for I verily think that the velocity of the Earths
tion, not onely under the Equinoctial, but in our paralel alſo, is
greater than that of the ball whilſt it moveth in the Piece; ſo that
the interval C E would be abſolutely much bigger than the whole
length of the Piece, and the inclination of the tranſverſe line
ſequently bigger than half a right angle: but be the velocity of
the Earth more, or be it leſs, in compariſon of the velocity of the
fire, this imports nothing; for if the velocity of the Earth be ſmall,
and conſequently the inclination of the tranſverſe line be little
alſo; there is then alſo need but of little inclination to make the

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