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

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1your gun ſtill; and if the mark ſhall move, the gun muſt be kept upon
the mark by moving.
And upon this dependeth the proper anſwer

to the other argument taken from the ſhot of a Canon, at the
mark placed towards the South or North: wherein is alledged,
that if the Earth ſhould move, the ſhots would all range
ward of the mark, becauſe that in the time whilſt the ball, being
forc'd out of the Piece, goeth through the air to the mark, the ſaid
mark being carried toward the Eaſt, would leave the ball to the
Weſtward.
I anſwer therefore, demanding whether if the
non be aimed true at the mark, and permitted ſo to continue, it
will conſtantly hit the ſaid mark, whether the Earth move or ſtand
ſtill?
It muſt be replied, that the aim altereth not at all, for if
the mark doth ſtand ſtill, the Piece alſo doth ſtand ſtill, and if it,
being tranſported by the Earths motion, doth move, the Piece doth
alſo move at the ſame rate, and, the aim maintained, the ſhot
proveth always true, as by what hath been ſaid above, is
feſt.
The manner how
Fowlers ſhoot birds
flying.
The anſwer to
the objection tak n
from the ſhots of
towards the North
and South.
SAGR. Stay a little, I entreat you, Salviatus, till I have
pounded a certain conceit touching theſe ſhooters of birds flying,
whoſe proceeding I believe to be the ſame which you relate, and
believe the effect of hitting the bird doth likewiſe follow: but yet
I cannot think that act altogether conformable to this of ſhooting
in great Guns, which ought to hit as well when the piece and mark
moveth, as when they both ſtand ſtill; and theſe, in my opinion,
are the particulars in which they diſagree.
In ſhooting with a
great Gun both it and the mark move with equal velocity, being
both tranſported by the motion of the Terreſtrial Globe: and
beit ſometimes the piece being planted more towards the Pole,
than the mark, and conſequently its motion being ſomewhat
er than the motion of the mark, as being made in a leſſer circle,
ſuch a difference is inſenſible, at that little diſtance of the piece
from the mark: but in the ſhot of the Fowler the motion of the
Fowling-piece wherewith it goeth following the bird, is very ſlow
in compariſon of the flight of the ſaid bird; whence me thinks it
ſhould follow, that that ſmall motion which the turning of the
Birding-piece conferreth on the bullet that is within it, cannot,
when it is once gone forth of it, multiply it ſelf in the air, untill it
come to equal the velocity of the birds flight, ſo as that the ſaid bullet
ſhould always keep direct upon it: nay, me thinketh the bird
would anticipate it and leave it behind.
Let me add, that in this
act, the air through which the bullet is to paſs, partaketh not of the
motion of the bird: whereas in the caſe of the Canon, both it,
the mark, and the intermediate air, do equally partake of the
mon diurnal motion.
So that the true cauſe of the Marks-man
his hitting the mark, as it ſhould ſeem, moreover and beſides the