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

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1other Operation. And then, the being to make greater Reſiſtance
at one time than at another, from what other doth it proceed, but
only from its being aſſailed at one time with a greater Impetus and
Velocity, and at another time with leſſer?
And if this be ſo then the
ſame quantity of the Velocity of the Moveable is at once the Cauſe
and the Mealure of the quantity of the Reſiſtance.
Therefore all
Motions, whether they be ſlow or ſwift, are retarded and impe­
ded in the ſame proportion: a Notion in my judgment not con­
temptible.
SALV. We may alſo in this ſecond caſe conclude, That the
Fallacies in the Concluſions, which are demonſtrated, abſtracting
from the extern Accidents, are in our Inſtruments of very ſmall
conſideration, in reſpect of the Motions of great Velocities of
which for the moſt part we ſpeak, and of the Diſtances which are
but very ſmall in relation to the Semidiameter and great Circles of
the Terreſtrial Globe.
SIMP. I would gladly hear the reaſon why you ſequeſtrate
the Projects from the Impetus of the Fire, that is, as I conceive from
the force of the Powder, from the other Projects made by Slings,
Bows, or Croſs-bows, touching their not being in the ſame manner
ſubject to the Acceleration and Impediment of the Air.
SALV. I am induced thereto by the exceſſive, and, as I may ſay,
Supernatural Fury or Impetuouſneſs with which thoſe Projects are
driven out: For indeed I think that the Velocity with which a Bul­
let is ſhot out of a Musket or Piece of Ordinance may without any
Hyperbole be called Supernatural.
For one of thoſe Bullets de­
ſcending naturally thorow the Air from ſome immenſe height, its
Velocity, by reaſon of the Reſiſtance of the Air will not go in­
creaſing perpetually: but that which in Cadent Bodies of ſmall
Gravity is ſeen to happen in no very great ^{*} Space, I mean their

being reduced in the end to an Equable Motion, ſhall alſo happen
after a Deſcent of thouſands of yards, in a Ball of Iron or Lead:
and this determinate and ultimate Velocity may be ſaid to be the
greateſt that ſuch a Body can obtain or acquire thorow the Air:
which Velocity I account to be much leſſer than that which cometh
to be impreſſed on the ſame Ball by the fired Powder. And of this
a very appoſite Experiment may advertiſe us.
At an height of an
hundred or more yards let off a Musket charged with a Leaden
Bullet perpendicularly downwards upon a Pavement of Stone; and
with the ſame Musket ſhoot againſt ſuch another Stone at the Di­
ſtance of a yard or two, and then ſee which of the two Bullets is
more flatted: for if that coming from on high be leſs ^{*} dented than

the other, it ſhall be a ſign that the Air hath impeded it, and dimi­
niſhed the Velocity conferred upon it by the Fire in the beginning
of the Motion: and that, conſequently, ſo great a Velocity the Air

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