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

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1is, fifteen firſt minutes of a degree, in one firſt minute of an hour;
that is, fifteen ſeconds of a degree, in one ſecond of an hour; and
becauſe one ſecond is the time of the ſhot, therefore in this time
the Weſtern horizon riſeth fifteen ſeconds of a degree, and ſo
much likewiſe the mark; and therefore fifteen ſeconds of that
cle, whoſe ſemidiameter is five hundred paces (for ſo much the
ſtance of the mark from the Piece was ſuppoſed.) Now let us
look in the table of Arches and Chords (ſee here is Copernicus his
book) what part is the chord of fifteen ſeconds of the
ter, that is, five hundred paces.
Here you ſee the chord (or
tenſe) of a firſt minute to be leſs than thirty of thoſe parts, of
which the ſemidiameter is an hundred thouſand.
Therefore the
chord of a ſecond minute ſhall be leſs then half of one of thoſe
parts, that is leſs than one of thoſe parts, of whichthe
ter is two hundred thouſand; and therefore the chord of fifteen
conds ſhall be leſs than fifteen of thoſe ſame two hundred thouſand
parts; but that which is leſs than (a) fifteen parts of two hun­

dred thouſand, is alſo more than that which is four centeſmes of
five hundred; therefore the aſcent of the mark in the time of the
balls motion is leſſe than four centeſmes, that is, than one twenty
fifth part of a pace; it ſhall be therefore (b) about two inches:
And ſo much conſequently ſhall be the variation of each Weſtern
ſhot, the Earth being ſuppoſed to have a diurnal motion.
Now if I
ſhall tell you, that this variation (I mean of falling two inches ſhort
of what they would do in caſe the Earth did not move) upon

all doth happen in all ſhots, how will you convince me Simplicius,
ſhewing me by an experiment that it is not ſo?
Do you not ſee
that it is impoſſible to confute me, unleſs you firſt find out a way
to ſhoot at a mark with ſo much exactneſſe, as never to miſſe an
hairs bredth?
For whilſt the ranges of great ſhot conſiſt of
rent numbers of paces, as de facto they do, I will affirm that in
each of thoſe variations there is contained that of two inches
ſed by the motion of the Earth.
(a) That is, in
plainer termes the
fraction 15/200000, is
more than the
ction 4/50000, for
viding the
nators by their
minators, and the
firſt produceth
13333 1/3 the other
but 12500.
(b) It ſhall be
neer 2 2/5 inches,
counting the pace
to be Geometrical,
containing 5 foot.
SAGR. Pardon me, Salviatus, you are too liberal. For I would

tell the Peripateticks, that though every ſhot ſhould hit the very
centre of the mark, that ſhould not in the leaſt diſprove the motion
of the Earth.
For the Gunners are ſo conſtantly imployed in
velling the ſight and gun to the mark, as that they can hit the ſame,
notwithſtanding the motion of the Earth.
And I ſay, that if the
Earth ſhould ſtand ſtill, the ſhots would not prove true; but the
Occidental would be too low, and the Oriental too high: now let
Simplicius diſprove me if he can.
It is
ted with great
tilty, that the
Earths motion
poſed, Canon ſhot
ought not to vary
more than in reſt.
SALV. This is a ſubtilty worthy of Sagredus: But whether
this variation be to be obſerved in the motion, or in the reſt of the
Earth, it muſt needs be very ſmall, it muſt needs be ſwallowed up

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