A Discourse Presented to the Most Serene Don Cosimo II., Great Duke of Tuscany, Concerning the Natation of Bodies Vpon, and Submersion In, the Water.Galilei, Galileo
Science
A Discourse Presented to the Most Serene Don Cosimo II., Great Duke of Tuscany, Concerning the Natation of Bodies Vpon, and Submersion In, the Water.
Galilei, Galileo
Hydrostatics; Specific gravity
[50] Neither Figure, nor the breadth of Figure, is the Cause of
Natation.
Some peradventure, by way of defence, may say, that wetting the Board
of Ebony, and that in the superiour Superficies, it would, though of
it self unable to pierce and penetrate the water, be born downwards,
if not by the weight of the additionall water, at least by that desire
and propension that the superiour parts of the water have to re-unite
and rejoyn themselves: by the Motion of which parts, the said Board
cometh in a certain manner, to be depressed downwards.
[Sidenote: The Bathed Solid descends not out of any affectation
of union in the upper parts of the water.]
This weak Refuge will be removed, if we do but consider, that the
repugnancy of the inferiour parts of the water, is as great against
Dis-union, as the Inclination of its superiour parts is to union: nor
can the uper unite themselves without depressing the board, nor can it
descend without disuniting the parts of the nether Water: so that it
doth follow, by necessary consequence, that for those respects, it
shall not descend. Moreover, the same that may be said of the upper
parts of the water, may with equall reason be said of the nether,
namely, that desiring to unite, they shall force the said Board
upwards.
Happily, some of these Gentlemen that dissent from me, will wonder,
that I affirm, that the contiguous superiour Air is able to sustain
that Plate of Brass or of Silver, that stayeth above water; as if I
would in a certain sence allow the Air[51], a kind of Magnetick vertue of
sustaining the grave Bodies, with which it is contiguous. To satisfie
all I may, to all doubts, I have been considering how by some other
sensible Experiment I might demonstrate, how truly that little
contiguous and superiour Air sustaines those Solids, which being by
nature apt to descend to the Bottom, being placed lightly on the water
submerge not, unless they be first thorowly bathed; and have found,
that one of these Bodies having descended to the Bottom, by
conveighing to it (without touching it in the least) a little Air,
which conjoyneth with the top of the same, it becometh sufficient, not
only, as before to sustain it, but also to raise it, and to carry it
back to the top, where it stays and abideth in the same manner, till
such time, as the assistance of the conjoyned Air is taken away. And
to this effect, I have taken a Ball of Wax, and made it with a little
Lead, so grave, that it leasurely descends to the Bottom, making with
all its Superficies very smooth and pollite: and this being put gently
into the water, almost wholly submergeth, there remaining vissible
only a little of the very top[52], the which so long as it is conjoyned
with the Air, shall retain the Ball a-top, but the Contiguity of the
Air taken away by wetting it, it shall descend to the Bottom and there
remain. Now to make it by vertue of the Air, that before sustained it
Public-domain text, read in full here on John Shaqi.
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