1round upon their centres with equal velocities, ſo as that two

veables, which ſuppoſe for example to be two ſtones placed in the

points B and C, come to be carried along the circumferences B G

and C E, with equal velocities; ſo that in the ſame time that the

ſtone B ſhall have run the arch B G, the ſtone C will have paſt the

arch C E. I ſay now, that the whirl or vertigo of the leſſer wheel

is much more potent to make the projection of the ſtone B, than

the vertigo of the bigger wheel to make that of the ſtone C.

Therefore the projection, as we have already declared, being to be

made along the tangent, when the ſtones B and C are to ſeparate

from their wheels, and to begin the motion of projection from the

points B and C, then ſhall they be extruded by the impetus

ceived from the vertigo by (or along) the tangents B F and C D.

The two ſtones therefore have equal impetuoſities of running

long the tangents B F and C D, and would run along the ſame, if

they were not turn'd aſide by ſome other force: is it not ſo

gredus?

veables, which ſuppoſe for example to be two ſtones placed in the

points B and C, come to be carried along the circumferences B G

and C E, with equal velocities; ſo that in the ſame time that the

ſtone B ſhall have run the arch B G, the ſtone C will have paſt the

arch C E. I ſay now, that the whirl or vertigo of the leſſer wheel

is much more potent to make the projection of the ſtone B, than

the vertigo of the bigger wheel to make that of the ſtone C.

Therefore the projection, as we have already declared, being to be

made along the tangent, when the ſtones B and C are to ſeparate

from their wheels, and to begin the motion of projection from the

points B and C, then ſhall they be extruded by the impetus

ceived from the vertigo by (or along) the tangents B F and C D.

The two ſtones therefore have equal impetuoſities of running

long the tangents B F and C D, and would run along the ſame, if

they were not turn'd aſide by ſome other force: is it not ſo

gredus?

SAGR. In my opinion the buſineſſe is as you ſay.

SALV. But what force, think you, ſhould that be which averts

the ſtones from moving by the tangents, along which they are

tainly driven by the impetus of the vertigo.

the ſtones from moving by the tangents, along which they are

tainly driven by the impetus of the vertigo.

SAGR. It is either their own gravity, or elſe ſome glutinous

matter that holdeth them faſt and cloſe to the wheels.

matter that holdeth them faſt and cloſe to the wheels.

SALV. But for the diverting of a moveable from the motion

to which nature inciteth it, is there not required greater or leſſer

force, according as the deviation is intended to be greater or

ſer? that is, according as the ſaid moveable in its deviation hath a

greater or leſſer ſpace to move in the ſame time?

to which nature inciteth it, is there not required greater or leſſer

force, according as the deviation is intended to be greater or

ſer? that is, according as the ſaid moveable in its deviation hath a

greater or leſſer ſpace to move in the ſame time?

SAGR. Yes certainly: for it was concluded even now, that to

make a moveable to move; the movent vertue muſt be increaſed

in proportion to the velocity wherewith it is to move.

make a moveable to move; the movent vertue muſt be increaſed

in proportion to the velocity wherewith it is to move.

SALV. Now conſider, that for the deviating the ſtone upon

the leſſe wheel from the motion of projection, which it would

make by the tangent B F, and for the holding of it faſt to the

wheel, it is required, that its own gravity draw it back the whole

length of the ſecant F G, or of the perpendicular raiſed from the

point G, to the line B F, whereas in the greater wheel the

on needs to be no more than the ſecant D E, or the

lar let fall from the tangent D G to the point E, leſſe by much

than F G, and alwayes leſſer and leſſer according as the wheel is

made bigger. And foraſmuch as theſe retractions (as I may call

them) are required to be made in equal times, that is, whil'ſt the

wheels paſſe the two equal arches B G and C E, that of the ſtone

B, that is, the retraction F G ought to be more ſwift than the

ther D E; and therefore much greater force will be required for

the leſſe wheel from the motion of projection, which it would

make by the tangent B F, and for the holding of it faſt to the

wheel, it is required, that its own gravity draw it back the whole

length of the ſecant F G, or of the perpendicular raiſed from the

point G, to the line B F, whereas in the greater wheel the

on needs to be no more than the ſecant D E, or the

lar let fall from the tangent D G to the point E, leſſe by much

than F G, and alwayes leſſer and leſſer according as the wheel is

made bigger. And foraſmuch as theſe retractions (as I may call

them) are required to be made in equal times, that is, whil'ſt the

wheels paſſe the two equal arches B G and C E, that of the ſtone

B, that is, the retraction F G ought to be more ſwift than the

ther D E; and therefore much greater force will be required for