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
its Resistance, which afterwards being arrived at the Air, stayeth
there, and hardly toucheth it; whence I may aswell say, that the water
is more easier divided than the Air.
[92] _Archimed. De Insident. humi_ lib. 2. prop. 1.
I will not on this occasion forbear to give warning of another fallacy
of these persons, who attribute the reason of sinking or swimming to
the greater or lesse Resistance of the Crassitude of the water against
Division, making use of the example of an Egg, which in sweet water
goeth to the bottom, but in salt water swims; and alledging for the
cause thereof, the faint Resistance of fresh water against Division,
and the strong Resistance of salt water. But if I mistake not, from
the same Experiment, we may aswell deduce the quite contrary; namely,
that the fresh water is more dense, and the salt more tenuous and
subtle, since an Egg from the bottom of salt water speedily ascends to
the top, and divides its Resistance, which it cannot do in the fresh,
in whose bottom it stays, being unable to rise upwards. Into such like
perplexities, do false Principles Lead men: but he that rightly
Philosophating, shall acknowledge the excesses of the Gravities of the
Moveables and of the Mediums, to be the Causes of those effects, will
say, that the Egg sinks to the bottom in fresh water, for that it is
more grave than it, and swimeth in the salt, for that its less grave
than it: and shall without any absurdity, very solidly establish his
Conclusions.
Therefore the reason totally ceaseth, that _Aristotle_ subjoyns in the
Text saying[93]; The things, therefore, which have great breadth remain
above, because they comprehend much, and that which is greater, is not
easily divided. Such discoursing ceaseth, I say, because its not true,
that there is in water or in Air any Resistance of Division; besides
that the Plate of Lead when it stays, hath already divided and
penetrated the Crassitude of the water, and profounded it self ten or
twelve times more than its own thickness: besides that such Resistance
of Division, were it supposed to be in the water, could not rationally
be affirmed to be more in its superiour parts than in the middle, and
lower: but if there were any difference, the inferiour should be the
more dense, so that the Plate would be no less unable to penetrate the
lower, than the superiour parts of the water; nevertheless we see that
no sooner do we wet the superiour Superficies of the Board or thin
Piece of Wood, but it precipitatly, and without any retension,
descends to the bottom.
[93] Text 45.
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