Galilei, Galileo - Discourse concerning the natation of bodies

Galilei, Galileo, Discourse concerning the natation of bodies, 1663

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T he Authors
confutation of
the Peripateticks
Cauſes of Nata
tion & Submerſi
on.

Water & other
fluids void of
Reſiſtance a
gainſt Diviſion.

T he predomi
nancy of Ele
ments in Move
ables to be con
ſidered only in
relation to their
excefs or defectus
of Gravity in
reference to the
Medium.

T he immedi
ate Cauſe of Na
tation is that the
Moveable is leſs
grave than the
Water.

T he Peripate
ticks alledge for
the reaſon of
Natation the
Cauſe of the
Cauſe.

Gravity a
Cauſe moſt per
ſpicuous to
ſence:

Let us not then deſpiſe thoſe Hints, though very dark, which
Reaſon, after ſome contemplation, offereth to our Intelligence, and
lets be content to be taught by Archimedes, that then any Body ſhall

ſubmerge in water, when it ſhall be ſpecifically more grave than it
and that if it ſhall be leſs grave, it ſhall of neceſſity ſwim, and

that it will reſt indifferently in any place under water, if its Gravity
be perfectly like to that of the water.

Lib 1. of Na
tation Prop. 7.

Id. Lib. 1.
Prop. 4.

Id. Lib. 1:
Prop. 3.

Theſe things explained and proved, I come to conſider that which
offers it ſelf, touching what the Diverſity of figure given unto the
ſaid Moveable hath to do with theſe Motions and Reſts; and pro
ceed to affirme, that,

THEOREME V.

The diverſity of Figures given to this or that Solid

cannot any way be a Cauſe of its abſolute Sinking or
Swimming.

Diverſity of
Figure no Cauſe
of its abſolute
Natation or Sub
merſion.

So that if a Solid being formed, for example, into a Spherical
Figure, doth ſink or ſwim in the water, I ſay, that being formed
into any other Figure, the ſame figure in the ſame water, ſhall
ſink or ſwim: nor can ſuch its Motion by the Expanſion or by o
ther mutation of Figure, be impeded or taken away.

The Expanſi
on of Figure, re
tards the Veloci
ty of the aſcent
or deſcent of the
Moveable in the
water; but doth
not deprive it of
all Motion.

The Expanſion of the Figure may indeed retard its Velocity, aſ
well of aſcent as deſcent, and more and more according as the ſaid Fi
gure is reduced to a greater breadth and thinneſs: but that it may bere
duced to ſuch a form as that that ſame matter be wholly hindred from
moving in the ſame water, that I hold to be impoſſible. In this I have
met with great contradictors, who producing ſome Experiments, and
in perticular a thin Board of Ebony, and a Ball of the ſame Wood
and ſhewing how the Ball in Water deſcended to the bottom, and
the Board being put lightly upon the Water ſubmerged not, but reſt
ed; have held, and with the Authority of Ariſtotle, confirmed them
ſelves in their Opinions, that the Cauſe of that Reſt was the breadth
of the Figure, u able by its ſmall weight to pierce and penetrate the
Reſiſtance of the Waters Craſſitude, which Reſiſtance is readily o
vercome by the other Sphericall Figure.

This is the Principal point in the preſent Queſtion, in which I per
ſwade my ſelf to be on the right ſide.

Therefore, beginning to inveſtigate with the examination of ex
quiſite Experiments that really the Figure doth not a jot alter the deſ
cent or Aſcent of the ſame Solids, and having already demonſtra
ted that the greater or leſs Gravity of the Solid in relation to the Gra
vity of the Medium is the cauſe of Deſcent or Aſcent: when ever we

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