Salusbury, Thomas, Mathematical collections and translations (Tome I), 1667

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1
SIMP. The top will run reeling along the floor towards that
part whither its upper parts encline it.
SAGR. And why not whither the contrary parts tend, namely,
thoſe which touch the ground?
SIMP. Becauſe thoſe upon the ground happen to be impeded
by the roughneſs of the touch, that is, by the floors unevenneſs;
but the ſuperiour, which are in the tenuous and flexible air, are
hindred very little, if at all; and therefore the top will obey their
inclination.
SAGR. So that that taction, if I may ſo ſay, of the neither
parts on the floor, is the cauſe that they ſtay, and onely the upper
parts ſpring the top forward.
SALV. And therefore, if the top ſhould fall upon the ice, or
other very ſmooth ſuperficies, it would not ſo well run forward, but
might peradventure continue to revolve in it ſelf, (or ſleep)
out acquiring any progreſſive motion.
SAGR. It is an eaſie thing for it ſo to do; but yet
leſs, it would not ſo ſpeedily come to ſleep, as when it falleth on
a ſuperficies ſomewhat rugged.
But tell me, Simplicius, when
the top turning round about it ſelf, in that manner, is let fall, why
doth it not move forwards in the air, as it doth afterwards when it
is upon the ground?
SIMP. Becauſe having air above it, and beneath, neither thoſe
parts, nor theſe have any where to touch, and not having more
caſion to go forward than backward, it falls perpendicularly.
SAGR. So then the onely reeling about its ſelf, without other
impetus, can drive the top forward, being arrived at the ground,
very nimbly.
Now proceed we to what remains. That laſh,
which the driver tyeth to his Top-ſtick, and with which, winding
it about the top, he ſets it (i. e. makes it go) what effect hath it on
the ſaid top?
SIMP. It conſtrains it to turn round upon its toe, that ſo it may
free it ſelf from the Top-laſh.
SAGR. So then, when the top arriveth at the ground, it cometh
all the way turning about its ſelf, by means of the laſh.
Hath it
not reaſon then to move in it ſelf more ſwiftly upon the ground,
than it did whilſt it was in the air?
SIMP. Yes doubtleſs; for in the air it had no other impulſe
than that of the arm of the projicient; and if it had alſo the
ing, this (as hath been ſaid) in the air drives it not forward at all:
but arriving at the floor, to the motion of the arm is added the
progreſſion of the reeling, whereby the velocity is redoubled.
And
I know already very well, that the top skipping from the ground,
its velocity will deminiſh, becauſe the help of its circulation is
wanting; and returning to the Earth will get it again, and by that