|Salusbury, Thomas Mathematical collections and translations 1667|
offer upon some other day: but I would not have Sagredus of
fended at this digression.
SAGR. I am rather very much pleased with it, for that I re
member that when I studied Logick, I could never comprehend that
so much cry'd up and most potent demonstration of Aristotle.
SALV. Let us go on therefore; and let Simplicius, tell me
what that motion is which the stone maketh that is held fast in the
slit of the sling, when the boy swings it about to throw it a great
SIMP. The motion of the stone, so long as it is in the slit, is
circular, that is, moveth by the arch of a circle, whose stedfast
centre is the knitting of the shoulder, and its semi-diameter the arm
SALV. And when the stone leaveth the sling, what is its mo
tion? Doth it continue to follow its former circle, or doth it go
by another line?
SIMP. It will continue no longer to swing round, for then it
would not go farther from the arm of the projicient, whereas
we see it go a great way off.
SALV. With what motion doth it move then?
SIMP. Give me a little time to think thereof; For I have ne
ver considered it before.
SALV. Hark hither, Sagredus; this is the Quoddam reminisci
in a subject well understood. You have paused a great while,
SIMP. As far as I can see, the motion received in going out of
the sling, can be no other than by a right line; nay, it must ne
cessarily be so, if we speak of the pure adventitious impetus. I
was a little puzled to see it make an arch, but because that arch
bended all the way upwards, and no other way, I conceive that
that incurvation cometh from the gravity of the stone, which na
turally draweth it downwards. The impressed impetus, I say,
without respecting the natural, is by a right line.
The motion im
pressed by the pro
jicient is onely by a
SALV. But by what right line? Because infinite, and towards
every side may be produced from the slit of the sling, and from the
point of the stones separation from the sling.
SIMP. It moveth by that line which goeth directly from the
motion which the stone made in the sling.
SALV. The motion of the stone whilst it was in the slit, you
have affirmed already to be circular; now circularity opposeth
directness, there not being in the circular line any part that is di
rect or streight.
SIMP I mean not that the projected motion is direct in re
spect of the whole circle, but in reference to that ultimate point,
where the circular motion determineth. I know what I would