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

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1holding faſt the ſtone B to its little wheel, than for the holding
the ſtone C to its great one, which is as much as to ſay, that ſuch
a ſmall thing will impede the extruſion in the great wheel, as will
not at all hinder it in the little one.
It is manifeſt therefore that
the more the wheel augmenteth, the more the cauſe of the
jection diminiſheth.
SAGR. From this which I now underſtand, by help of your
nute diſſertation, I am induced to think, that I am able to ſatisfie
my judgment in a very few words.
For equal impetus being
preſſed on both the ſtones that move along the tangents, by the
equal velocity of the two wheels, we ſee the great circumference,
by means of its ſmall deviation from the tangent, to go ſeconding,
as it were, and in a fair way refraining in the ſtone the appetite, if
I may ſo ſay, of ſeparating from the circumference; ſo that any
ſmall retention, either of its own inclination, or of ſome
tion ſufficeth to hold it faſt to the wheel.
Which, again, is not
ble to work the like effect in the little wheel, which but little
ſecuting the direction of the tangent, ſeeketh with too much
gerneſſe to hold faſt the ſtone; and the reſtriction and glutination
not being ſtronger than that which holdeth the other ſtone faſt to

the greater wheel, it ^{*} breaks looſe, and runneth along the
Therefore I do not only finde that all thoſe have erred,
who have believed the cauſe of the projection to increaſe
ding to the augmentation of the vertigo's velocity; but I am
further thinking, that the projection diminiſhing in the inlarging of
the wheel, ſo long as the ſame velocity is reteined in thoſe wheels;
it may poſſibly be true, that he that would make the great wheel
extrude things like the little one, would be forced to increaſe
them as much in velocity, as they increaſe in diameter, which he
might do, by making them to finiſh their converſions in equal
times; and thus we may conclude, that the Earths revolution or
vertigo would be no more able to extrude ſtones, than any little
wheel that goeth ſo ſlowly, as that it maketh but one turn in
ty four hours.
* Strappar la
vezza, is to break
the bridle.
SALV. We will enquire no further into this point for the
ſent: let it ſuffice that we have abundantly (if I deceive not my
ſelf) demonſtrated the invalidity of the argument, which at firſt
ſight ſeemed very concluding, and was ſo held by very famous
men: and I ſhall think my time and words well beſtowed, if I
have but gained ſome belief in the opinion of Simplicius, I will
not ſay or the Earths mobility, but only that the opinion of thoſe
that believe it, is not ſo ridiculous and fond, as the rout of vulgar
Philoſophers eſteem it.
SIMP. The anſwers hitherto produced againſt the arguments
brought againſt this Diurnal Revolution of the Earth taken from

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