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

#### List of thumbnails

< >
 141 142 143 144 145 146 147 148 149 150
< >
page |< < of 701 > >|
1tarding, as being contrary to nature; and would be longer or
ſhorter, according to the greater or leſs impulſe, and according to
the greater or leſs acclivity.
SALV. It ſeems, then, that hitherto you have explained to me
the accidents of a moveable upon two different Planes; and that
in the inclining plane, the grave moveable doth ſpontaneouſly
ſcend, and goeth continually accelerating, and that to retain it in
reſt, force muſt be uſed therein: but that on the aſcending plane,
there is required a force to thruſt it forward, and alſo to ſtay it in
reſt, and that the motion impreſſed goeth continually diminiſhing,
till that in the end it cometh to nothing.
You ſay yet farther,
that in both the one and the other caſe, there do ariſe differences
from the planes having a greater or leſs declivity or acclivity; ſo
that the greater inclination is attended with the greater velocity;
and contrariwiſe, upon the aſcending plane, the ſame moveable
thrown with the ſame force, moveth a greater diſtance, by how
much the elevation is leſs.
Now tell me, what would befall the
ſame moveable upon a ſuperficies that had neither acclivity nor
declivity?
SIMPL. Here you muſt give me a little time to conſider of an
anſwer.
There being no declivity, there can be no natural
nation to motion: and there being no acclivity, there can be no
reſiſtance to being moved; ſo that there would ariſe an
rence between propenſion and reſiſtance of motion; therefore,
methinks it ought naturally to ſtand ſtill.
But I had forgot my
ſelf: it was but even now that Sagredus gave me to underſtand
that it would ſo do.
SALV. So I think, provided one did lay it down gently: but
if it had an impetus given it towards any part, what would
low?
SIMP. There would follow, that it ſhould move towards that
part.
SALV. But with what kind of motion? with the continually
accelerated, as in declining planes; or with the ſucceſſively
tarded, as in thoſe aſcending.
SIMP. I cannot tell how to diſcover any cauſe of acceleration,
or retardation, there being no declivity or acclivity.
SALV. Well: but if there be no cauſe of retardation, much
leſs ought there to be any cauſe of reſt.
How long therefore
would you have the moveable to move?
SIMP. As long as that ſuperficies, neither inclined nor
ned ſhall laſt.
SALV. Therefore if ſuch a ſpace were interminate, the motion
upon the ſame would likewiſe have no termination, that is, would
be perpetual.