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

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1with that which hath been ſaid already, namely, that in caſe the
Earth ſhould move, the ſhots made Eaſtward would prove too
high, &c.
the ball, as it is probable, being to move along the
SALV. But if I ſhould ſay, that ſo it falleth out upon triall,
how would you cenſure me?
SIMP. It is neceſſary to proceed to experiments for the
ving of it.
SALV. But do you think, that there is to be found a Gunner ſo
skilful, as to hit the mark at every ſhoot, in a diſtance of v.g. five
hundred paces?
SIMP. No Sir; nay I believe that there is no one, how good a
marks-man ſoever that would promiſe to come within a pace of
the mark,
SALV. How can we then, with ſhots ſo uncertain, aſſure our
ſelves of that which is in diſpute?
SIMP. We may be aſſured thereof two wayes; one, by
king many ſhots; the other, becauſe in reſpect of the great
city of the Earths motion, the deviation from the mark would in
my opinion be very great.
SALV. Very great, that is more than one pace; in regard that
the varying ſo much, yea and more, is granted to happen ordinarily
even in the Earths mobility.
SIMP. I verily believe the variation from the mark would be
more than
A Computation
how much the
ges of great ſhot
ought to vary from
the marke, the
Earths motion
ing granted.
SALV. Now I deſire that for our ſatisfaction we do make thus
in groſſe a ſlight calculation, if you conſent thereto, which will
ſtand us in ſtead likewiſe (if the computation ſucceed as I expect)
for a warning how we do in other occurrences ſuffer our ſelves, as
the ſaying is, to be taken with the enemies ſhouts, and ſurrender
up our belief to what ever firſt preſents it ſelf to our fancy.
now to give all advantages to the Peripateticks and Tychonicks,
let us ſuppoſe our ſelves to be under the Equinoctial, there to ſhoot
a piece of Ordinance point blank Eaſtwards at a mark five
dred paces off.
Firſt, let us ſee thus (as I ſaid) in a level, what
time the ſhot after it is gone out of the Piece taketh to arrive at
the mark; which we know to be very little, and is certainly no
more than that wherein a travailer walketh two ſteps, which alſo
is leſs than the ſecond of a minute of an hour; for ſuppoſing
that the travailer walketh three miles in an hour, which are nine
thouſand paces, being that an hour containes three thouſand, ſix
hundred ſecond minutes, the travailer walketh two ſteps and an
half in a ſecond, a ſecond therefore is more than the time of the
balls motion.
And for that the diurnal revolution is twenty four
hours, the Weſtern horizon riſeth fifteen degrees in an hour, that

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