1to be the Altitude, and C B the Amplitude of the Semiparabola A B;
which is deſcribed by the Compoſition of two Lations; of which one is
that of the Moveable deſcending along A C with a Motion Naturally
Acceler ate ex quiete in A; the other is the Equable Tranſverſal Moti
on according to the Horizontal Line A D. The Impetus acquired in C
along the Deſcent A C is determined by the quantity of the ſaid height
A C; for the Impetus of a Moveable
149[Figure 149]
falling from the ſame height is alwaies
one and the ſame: but in the Horizontal
Line one may aſſign not one, but innume
rable Degrees of Velocities of Equable
Motions: out of which multitude that I
may ſingle out, and as it were point with
the finger to that which I make choice of,
I extend or prolong the Altitude C A in
ſublimi, in which, as was done before, I
will pitch upon A E; from which if I
conceive in my mind a Moveable to fall
ex quiete in E, it appeareth that its Im
petus acquired in the Time A, is one with which I conceive the ſame
Moveable being turned along A D to be moved; and its degree of
Vclocity to be that, which in the Time of the Deſcent along E A paſſeth
a Space in the Horizon double to the ſaid E A. This Præmonition I
judged neceſſary.
which is deſcribed by the Compoſition of two Lations; of which one is
that of the Moveable deſcending along A C with a Motion Naturally
Acceler ate ex quiete in A; the other is the Equable Tranſverſal Moti
on according to the Horizontal Line A D. The Impetus acquired in C
along the Deſcent A C is determined by the quantity of the ſaid height
A C; for the Impetus of a Moveable
149[Figure 149]falling from the ſame height is alwaies
one and the ſame: but in the Horizontal
Line one may aſſign not one, but innume
rable Degrees of Velocities of Equable
Motions: out of which multitude that I
may ſingle out, and as it were point with
the finger to that which I make choice of,
I extend or prolong the Altitude C A in
ſublimi, in which, as was done before, I
will pitch upon A E; from which if I
conceive in my mind a Moveable to fall
ex quiete in E, it appeareth that its Im
petus acquired in the Time A, is one with which I conceive the ſame
Moveable being turned along A D to be moved; and its degree of
Vclocity to be that, which in the Time of the Deſcent along E A paſſeth
a Space in the Horizon double to the ſaid E A. This Præmonition I
judged neceſſary.
It is moreover to be advertized that the Amplitude of the Semi
parabola A B ſhall be called by me the Horizontal Line [or Plane]
C B.
parabola A B ſhall be called by me the Horizontal Line [or Plane]
C B.
The Altitude, to with A C, the Axis of the ſaid Parabola.
And the Line E A, by whoſe Deſcent the Horizontal Impetus is de
termined, I call the Sublimity, or height.
termined, I call the Sublimity, or height.
Theſe things being declared and defined, I proceed to Demonſtra
tion.
tion.
SAGR. Stay, I pray you, for here me thinks it is convenient to
adorn this Opinion of our Author with the conformity of it to
the Conceit of Plato about the determining the different Veloci
ties of the Equable Motions of the Revolutions of the Cœleſtial
Bodies; who, having perhaps had a conjecture that no Moveable
could paſſe from Reſt into any determinate degree of Velocity in
which it ought afterwards to be perpetuated, unleſs by paſſing
thorow all the other leſſer degrees of Velocity, or, if you will,
greater degrees of Tardity, which interpoſe between the aſſigned
degree, and the higheſt degree of Tardity, that is of Reſt, ſaid that
God after he had created the Moveable Cœleſtial Bodies that he
might aſſign them thoſe Velocities wherewith they were afterwards
adorn this Opinion of our Author with the conformity of it to
the Conceit of Plato about the determining the different Veloci
ties of the Equable Motions of the Revolutions of the Cœleſtial
Bodies; who, having perhaps had a conjecture that no Moveable
could paſſe from Reſt into any determinate degree of Velocity in
which it ought afterwards to be perpetuated, unleſs by paſſing
thorow all the other leſſer degrees of Velocity, or, if you will,
greater degrees of Tardity, which interpoſe between the aſſigned
degree, and the higheſt degree of Tardity, that is of Reſt, ſaid that
God after he had created the Moveable Cœleſtial Bodies that he
might aſſign them thoſe Velocities wherewith they were afterwards
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