14

SAGR. I do not very well understand the question.

SALV. I will express it better by drawing a Figure: therefore
I will suppose the line A B [in Fig. 3.] parallel to the Horizon,
and upon the point B, I will erect a perpendicular B C; and after
that I adde this slaunt line C A. Understanding now the line C
A to be an inclining plain exquisitely polished, and hard, upon
which descendeth a ball perfectly round and of very hard matter,
and such another I suppose freely to descend by the perpendicular
C B: will you now confess that the impetus of that which de­
scends by the plain C A, being arrived to the point A, may be
equal to the impetus acquired by the other in the point B, after
the descent by the perpendicular C B?

The impetuosity of
moveables equally
approaching to the
centre, are equal.

SAGR. I resolutely believe so: for in effect they have both the
same proximity to the centre, and by that, which I have already
granted, their impetuosities would be equally sufficient to re-carry
them to the same height.

SALV. Tell me now what you believe the same ball would do
put upon the Horizontal plane A B?

Vpon an horizon­
tall plane the move­
able lieth still.

SAGR. It would lie still, the said plane having no declination.

SALV. But on the inclining plane C A it would descend, but
with a gentler motion than by the perpendicular C B?

SAGR. I may confidently answer in the affirmative, it seem­
ing to me necessary that the motion by the perpendicular C B
should be more swift, than by the inclining plane C A; yet ne­
vertheless, is this be, how can the Cadent by the inclination ar­
rived to the point A, have as much impetus, that is, the same de­
gree of velocity, that the Cadent by the perpendicular shall have
in the point B? these two Propositions seem contradictory.

The veloeity by the
inclining plane e­
qual to the veloci­
ty by the perpendi­
oular, and the mo­
tion by the perpen­
dicular swifter
than by the incli­
nation.

SALV. Then you would think it much more false, should I
say, that the velocity of the Cadents by the perpendicular, and
inclination, are absolutely equal: and yet this is a Proposition
most true, as is also this that the Cadent moveth more swiftly by
the perpendicular, than by the inclination.

SAGR. These Propositions to my ears sound very harsh: and
I believe to yours Simplicius?

SIMPL. I have the same sense of them.

SALV. I conceit you jest with me, pretending not to compre­
hend what you know better than my self: therefore tell me Sim­
plicius, when you imagine a moveable more swift than ano­
ther, what conceit do you fancy in your mind?

SIMPL. I fancie one to pass in the same time a greater space
than the other, or to move equal spaces, but in lesser time.

SALV. Very well: and for moveables equally swift, what's
your conceit of them?

SIMPL. I fancie that they pass equal spaces in equal times.