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
Whether Figure have any influence upon the encrease or diminution of
the Resistance in any Weight against its being raised in the Air[78]; and
I suppose, that I am to maintain the Affirmative, asserting that a
Mass of Lead, reduced to the Figure of a Ball, shall be raised with
less force, then if the same had been made into a thinne and broad
Plate, because that it in this spacious Figure, hath a great quantity
of Air to penetrate, and in that other, more compacted and contracted
very little: and to demonstrate the truth of such my Opinion, I will
hang in a small thred first the Ball or Bullet, and put that into the
water, tying the thred that upholds it to one end of the Ballance that
I hold in the Air, and to the other end I by degrees adde so much
Weight, till that at last it brings up the Ball of Lead out of the
water: to do which, suppose a Gravity of thirty Ounces sufficeth; I
afterwards reduce the said Lead into a flat and thinne Plate, the
which I likewise put into the water, suspended by three threds, which
hold it parallel to the Surface of the water, and putting in the same
manner, Weights to the other end, till such time as the Plate comes to
be raised and drawn out of the water: I finde that thirty six ounces
will not suffice to seperate it from the water, and raise it thorow
the Air: and arguing from this Experiment, I affirm, that I have fully
demonstrated the truth of my Proposition. Here my Oponents desires me
to look down, shewing me a thing which I had not before observed, to
wit, that in the Ascent of the Plate out of the water, it draws after
it another Plate (_if I may so call it_) of water, which before it
divides and parts from the inferiour Surface of the Plate of Lead, is
raised above the Levell of the other water, more than the thickness of
the back of a Knife: Then he goeth to repeat the Experiment with the
Ball, and makes me see, that it is but a very small quantity of water,
which cleaves to its compacted and contracted Figure: and then he
subjoynes, that its no wonder, if in seperating the thinne and broad
Plate from the water, we meet with much greater Resistance, than in
seperating the Ball, since together with the Plate, we are to raise a
great quantity of water, which occurreth not in the Ball: He telleth
me moreover, how that our Question is, whether the Resistance of
Elevation be greater in a dilated Plate of Lead, than in a Ball, and
not whether more resisteth a Plate of Lead with a great quantity of
water, or a Ball with a very little water: He sheweth me in the close,
that the putting the Plate and the Ball first into the water, to make
proofe thereby of their Resistance in the Air, is besides our case,
which treats of Elivating in the Air, and of things placed in the Air,
and not of the Resistance that is made in the Confines of the Air and
water, and by things which are part in Air and part in water: and
lastly, they make me feel with my hand, that when the thinne Plate is
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