SVPPOSITION.
I ſuppoſe that the degrees of Velocity acquired by the
ſame Moveable upon Planes of different inclinations
are equal then, when the Elevations of the ſaid
Planes are equal.
ſame Moveable upon Planes of different inclinations
are equal then, when the Elevations of the ſaid
Planes are equal.
By the Elevation of an inclined Plane he meaneth the Per
pendicular, which from the higher term of the ſaid Plane
falleth upon the Horizontal Line produced along by the
lower term of the ſaid Plane inclined: as for better underſtanding;
the Line A B being parallel to the Horizon, upon which let the two
81[Figure 81]
Planes C A, and C D be inclined:
the Perpendicular C B falling up
on the Horizontal Line B A the
Author calleth the Elevation
of the Planes C A and C D;
and ſuppoſeth that the degrees of
Velocity of the ſame Moveable
deſcending along the inclined Planes C A and C D, acqui
red in the Terms A and D are equal, for that their Elevation is
the ſame C B. And ſo great alſo ought the degree of Velocity be
underſtood to be which the ſame Moveable falling from the Point
C would acquire in the term B.
pendicular, which from the higher term of the ſaid Plane
falleth upon the Horizontal Line produced along by the
lower term of the ſaid Plane inclined: as for better underſtanding;
the Line A B being parallel to the Horizon, upon which let the two
81[Figure 81]Planes C A, and C D be inclined:
the Perpendicular C B falling up
on the Horizontal Line B A the
Author calleth the Elevation
of the Planes C A and C D;
and ſuppoſeth that the degrees of
Velocity of the ſame Moveable
deſcending along the inclined Planes C A and C D, acqui
red in the Terms A and D are equal, for that their Elevation is
the ſame C B. And ſo great alſo ought the degree of Velocity be
underſtood to be which the ſame Moveable falling from the Point
C would acquire in the term B.
SAGR. The truth is, this Suppoſition hath in it ſo much of pro
bability, that it deſerveth to be granted without diſpute, alwaies
preſuppoſing that all accidental and extern Impediments are re
moved, and that the Planes be very Solid and Terſe, and the Move
able in Figure moſt perfectly Rotund, ſo that neither the Plane,
nor the Moveable have any unevenneſs. All Contraſts and Im
pediments, I ſay, being removed, the light of Nature dictates to
me without any difficulty, that a Ball heavy and perfectly round
deſcending by the Lines C A, C D, and C B would come to the
terms A D, and B with equal Impetus's.
bability, that it deſerveth to be granted without diſpute, alwaies
preſuppoſing that all accidental and extern Impediments are re
moved, and that the Planes be very Solid and Terſe, and the Move
able in Figure moſt perfectly Rotund, ſo that neither the Plane,
nor the Moveable have any unevenneſs. All Contraſts and Im
pediments, I ſay, being removed, the light of Nature dictates to
me without any difficulty, that a Ball heavy and perfectly round
deſcending by the Lines C A, C D, and C B would come to the
terms A D, and B with equal Impetus's.
SALV. You argue very probably; but over and above the pro
bability, I will by an Experiment ſo increaſe the likelihood, as that
it wants but little of being equal to a very neceſſary Demonſtrati
on. Imagine this leafe of Paper to be a Wall erect at Right-angles
to the Horizon, and at a Nail, faſtned in the ſame, hang a Ball or
Plummet of Lead, weighing an ounce or two, ſuſpended by the
ſmall thread A B, two or three yards long, perpendicular to the
Horizon: and on the Wall draw an Horizontal Line D C, cutting
bability, I will by an Experiment ſo increaſe the likelihood, as that
it wants but little of being equal to a very neceſſary Demonſtrati
on. Imagine this leafe of Paper to be a Wall erect at Right-angles
to the Horizon, and at a Nail, faſtned in the ſame, hang a Ball or
Plummet of Lead, weighing an ounce or two, ſuſpended by the
ſmall thread A B, two or three yards long, perpendicular to the
Horizon: and on the Wall draw an Horizontal Line D C, cutting
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