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

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1contrary term, another intrinſick and natural quality, which

keth it averſe to motion.
Therefore tell me again; do you not
think that the inclination v. g. of grave bodies to move
wards, is equal to the reſiſtance of the ſame to the motion of
jection upwards?
The inclination of
grave bodies to the
motion downwards,
is equal to their
reſiſtance to the
motion upwards.
SAGR. I believe that it is exactly the ſame. And for this reaſon
I ſee that two equal weights being put into a ballance, they do
ſtand ſtill in equilibrium, the gravity of the one reſiſting its
ing raiſed by the gravity wherewith the other preſſing
wards would raiſe it.
SALV. Very well; ſo that if you would have one raiſe up the
other, you muſt encreaſe the weight of that which depreſſeth,
or leſſen the weight of the other.
But if the reſiſtance to
ing motion cunſiſt onely in gravity, how cometh it to paſſe, that

in ballances of unequal arms, to wit in the ^{*} Stiliard, a weight
ſometimes of an hundred pounds, with its preſſion downwards,
doth not ſuffice to raiſe up on of four pounds; that ſhall
poiſe with it, nay this of four, deſcending ſhall raiſe up that
of an hundred; for ſuch is the effect of the pendant weight upon
the weight which we would weigh?
If the reſiſtance to motion
reſideth onely in the gravity, how can the arm with its weight of
four pounds onely, reſiſt the weight of a ſack of wool, or bale of
ſilk, which ſhall be eight hundred, or a thouſand weight; yea
more, how can it overcome the ſack with its moment, and raiſe
it up?
It muſt therefore be confeſt Sagredus, that here it maketh
uſe of ſome other reſiſtance, and other force, beſides that of
ſimple gravity.
* A portable
lance wherewith
market-people
weigh their
modities, giving it
gravity by
ving the weight
farther from the
cock: call'd by the
Latines, Campana
trutina.
SAGR. It muſt needs be ſo; therefore tell me what this
cond virtue ſhould be.
SALV. It is that which was not in the ballance of equal
arms; you ſee then what variety there is in the Stiliard; and
on this doubtleſſe dependeth the cauſe of the new effect.
SAGR. I think that your putting me to it a ſecond time, hath
made me remember ſomething that may be to the purpoſe.
In
both theſe beams the buſineſs is done by the weight, and by the
motion; in the ballance, the motions are equal, and therefore the
one weight muſt exceed it in gravity before it can move it; in the
ſtiliard, the leſſer weight will not move the greater, unleſs when
this latter moveth little, as being ſlung at a leſſer diſtance, and the
other much, as hanging at a greater diſtance from the lacquet or
cock.
It is neceſſary therefore to conclude, that the leſſer weight
overcometh the reſiſtance of the greater, by moving much, whilſt
the other is moved but little.
SALV. Which is as much as to ſay, that the velocity of the
moveable leſs grave, compenſateth the gravity of the moveable
more grave and leſs