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

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SALV. Neither doth this ſuffice, but its requiſite to know
cording to what proportion ſuch accelleration is made; a
blem, that I believe was never hitherto underſtood by any
loſopher or Mathematician; although Philoſophers, and
larly the Peripateticks, have writ great and entire Volumes,
touching motion.
SIMP. Philoſophers principally buſie themſelves about
ſals; they find the definitions and more common ſymptomes,
mitting certain ſubtilties and niceties, which are rather
ſities to the Mathematicians.
And Aristotle did content himſelf
to deſine excellently what motion was in general; and of the
cal, to ſhew the principal qualities, to wit, that one is natural,
another violent; one is ſimple, another compound; one is
equal, another accellerate; and concerning the accelerate,
tents himſelf to give the reaſon of acceleration, remitting the
finding out of the proportion of ſuch acceleration, and other
particular accidents to the Mechanitian, or other inferiour
SAGR. Very well Simplicius. But you Salviatus, when you
deſcend ſometimes from the Throne of Peripatetick Majeſty,
have you ever thrown away any of your hours in ſtudying to find
this proportion of the acceleration of the motion of deſcending
grave bodies?
SALV. There was no need that I ſhould ſtudy for it, in regard
that the Academick our common friend, heretofore ſhewed me a
Treatiſe of his ^{*} De Motu, where this, and many other

dents were demonſtrated.
But it would be too great a digreſſion,
if for this particular, we ſhould interrupt our preſent diſcourſe,
(which yet it ſelf is alſo no better than a digreſſion) and make as
the Saying is, a Comedy within a Comedy.
This is that
cellent tract which
we give the firſt
place in our ſecond
SAGR. I am content to excuſe you from this narration for the
preſent, provided that this may be one of the Propoſitions
ved to be examined amongſt the reſt in another particular meeting,
for that the knowledg thereof is by me very much deſired; and
in the mean time let us return to the line deſcribed by the grave
body in its fall from the top of the Tower to its baſe.
SALV. If the right motion towards the centre of the Earth was
uniforme, the circular towards the Eaſt being alſo uniforme, you
would ſee compoſed of them both a motion by a ſpiral line, of
that kind with thoſe defined by Archimedes in his Book Dc
libus; which are, when a point moveth uniformly upon a right
line, whileſt that line in the mean time turneth uniformly about
one of its extreme points fixed, as the centre of his gyration.
But becauſe the right motion of grave bodies falling, is
ally accelerated, it is neceſſary, that the line reſulting of the

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