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
Brass, a Composition less grave than an equall quantity of Water: and
the place that the Vessel occupyeth in the Water whilst it floats, is
not equall to the Brass alone, but to the Brass and to the Air
together, which filleth that part of the Vessel that is below the
Levell of the water: Moreover, when the Water is infused, the Air is
removed, and there is a composition made of Brass and of water, more
grave _in specie_ than the simple water, but not by vertue of the
water infused, as having greater Specifick Gravity than the other
water, but through the proper Gravity of the Brass, and through the
alienation of the Air. Now, as he that should say that Brass, that by
its nature goes to the Bottom, being formed into the Figure of a
Ketle[50], acquireth from that Figure a vertue of lying in the Water
without sinking, would say that which is false; because that Brass
fashioned into any whatever Figure, goeth always to the Bottom,
provided, that that which is put into the water be simple Brass; and
it is not the Figure of the Vessel that makes the Brass to float, but
it is because that that is not purely Brass which is put into the
water, but an aggregate of Brass and of Air: so is it neither more nor
less false, that a thin Plate of Brass or of Ebony, swims by vertue of
its dilated & broad Figure: for the truth is, that it bares up without
submerging, because that that which is put in the water, is not pure
Brass or simple Ebony, but an aggregate of Brass and Air, or of Ebony
and Air. And, this is not contrary unto my Conclusion, the which,
(having many a time seen Vessels of Mettall, and thin pieces of
diverse grave Matters float, by vertue of the Air conjoyned with them)
did affirm, That Figure was not the Cause of the Natation or
Submersion of such Solids as were placed in the water. Nay more, I
cannot omit, but must tell my Antagonists, that this new conceit of
denying that the Superficies of the Board should be bathed, may beget
in a third person an opinion of a poverty of Arguments of defence on
their part, since that such bathing was never insisted upon by them in
the beginning of our Dispute, and was not questioned in the least,
being that the Originall of the discourse arose upon the swiming of
Flakes of Ice, wherein it would be simplicity to require that their
Superficies might bedry: besides, that whether these pieces of Ice be
wet or dry they alwayes swim, and as the Adversaries say, by reason of
the Figure.
[45] Water hath no Gravity in Water.
[46] Water deminisheth the Gravity of Solids immerged therein.
[47] The Experiment of a brass Ketle swiming when empty, & sinking
when full, alledged to prove that water gravitates in water,
answered.
[48] An Ocean sufficeth not to sink a Vessel specifically less
grave than water.
[49] Air, the Cause of the Natation of empty Vessels of Matters
graver _in specie_ than the water.
Public-domain text, read in full here on John Shaqi.
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