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

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1means move again faſter, than in the air. It onely reſts for me to
underſtand, whether in this ſecond motion on the Earth it move
more ſwiftly, than in the firſt; for then it would move in
tum, alwayes accelerating.
SAGR. I did not abſolutely affirm, that this ſecond motion is
more ſwift than the firſt; but that it may happen ſo to be
SIMP. This is that, which I apprehend not, and which I
deſire to know.
SAGR. And this alſo you know of your ſelf. Therefore tell
me: When you let the top fall out of your hand, without
king it turn round (i. e. ſetting it) what will it do at its coming to
the ground?
SIMP. Nothing, but there lie ſtill.
SAGR. May it not chance, that in its fall to the ground it may
acquire a motion?
Think better on it.
SIMP. Unleſſe we let it fall upon ſome inclining ſtone, as
children do playing at ^{*} Chioſa, and that falling ſide-wayes upon

the ſame, it do acquire the motion of turning round upon its toe,
wherewith it afterwards continueth to move progreſſively on the
floor, I know not in what other manner it can do any thing but
lie ſtill where it falleth.
* A Game in Italy,
which is, to glide
bullets down an
inclining ſtone,
SAGR. You ſee then that in ſome caſe it may acquire a new
When then the top jerked up from the ground, falleth
down again, why may it not caſually hit upon the declivity of
ſome ſtone fixed in the floor, and that hath an inclination that
way towards which it moveth, and acquiring by that ſlip a new
whirle over and above that conferred by the laſh, why may it
not redouble its motion, and make it ſwifter than it was at its
firſt lighting upon the ground?
SIMP. Now I ſee that the ſame may eaſily happen. And I
am thinking that if the top ſhould turn the contrary way, in
riving at the ground, it would work a contrary effect, that is,
the motion of the accidental whirl would retard that of the
SAGR. And it would ſometimes wholly retard and ſtop it, in
caſe the revolution of the top were very ſwift.
And from hence
riſeth the reſolution of that ſlight, which the more skilful Tennis
Players uſe to their advantage; that is, to gull their adverſary by
cutting (for ſo is their Phraſe) the Ball; which is, to return it
with a ſide Rachet, in ſuch a manner, that it doth thereby
quire a motion by it ſelf contrary to the projected motion, and ſo
by that means, at its coming to the ground, the rebound, which
if the ball did not turn in that manner, would be towards the
adverſary, giving him the uſual time to toſſe it back again, doth

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