Galilei, Galileo - Discourse concerning the natation of bodies

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

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peradventure not hitherto obſerved, cometh to meet with the ſaid
Board, rendering it no longer as it was before, whilſt it did fink more
ponderous than the water, but leſs.

Now, let us return to take the thin Plate of Gold, or of Silver, or the
thin Board of Ebony, and let us lay it lightly upon the water, ſo that it
ſtay there without ſinking, and diligently obſerve its effect. And
firſt, ſee how falſe the aſſertion of Aristotle, and our oponents is, to wit,
that it ſtayeth above water, through its unability to pierce and pene
trate the Reſiſtance of the waters Craſſitude: for it will manifeſtly
appear, not only that the ſaid Plates have penetrated the water, but
alſo that they are a conſiderable matter lower than the Surface of the
ſame, the which continueth eminent, and maketh as it were a Rampert
on all ſides, round about the ſaid Plates, the profundity of which they
ſtay ſwimming: and, according as the ſaid Plates ſhall be more grave
than the water, two, four, ten or twenty times, it is neceſſary, that
their Superficies do ſtay below the univerſall Surface of the water, ſo
much more, than the thickneſs of thoſe Plates, as we ſhal more diſtinctly
ſhew anon. In the mean ſpace, for the more eaſie underſtanding of what
I ſay, obſerve with me a little the preſent

[Figure 8]

Scheme: in which let us ſuppoſe the Surface
of the water to be diſtended, according to the
Lines F L D B, upon which if one ſhall put a
board of matter ſpecifically more grave than
water, but ſo lightly that it ſubmetge not, it
ſhall not reſt any thing above, but ſhall enter with its whole thickneſs
into the water: and, moreover, ſhall ſink alſo, as we ſee by the Board
A I, O I, whoſe breadth is wholly ſunk into the water, the little Ram
perts of water L A and D O incompaſſing it, whoſe Superficies is no
tably higher than the Superficies of the Board. See now whether it be
true, that the ſaid Board goes not to the Bottom, as being of Figure
unapt to penetrate the Craſſitude of the water.

But, if it hath already penetrated, and overcome the Continuity of

the water, & is of its own nature more grave than the ſaid water, why
doth it not proceed in its ſinking, but ſtop and ſuſpend its ſelf within
that little dimple or cavitie, which with its ponderoſity it hath made in
the water? I anſwer; becauſe that in ſubmerging it ſelf, ſo far as till its
Superficies come to the Levell with that of the water, it loſeth a part
of its Gravity, and loſeth the reſt of it as it ſubmergeth & deſcends be
neath the Surface of the water, which maketh Ramperts and Banks
round about it, and it ſuſtaines this loſs by means of its drawing after it,
and carrying along with it, the Air that is above it, and by Contact ad
herent to it, which Air ſucceeds to fill the Cavity that is invironed by
the Ramperts of water: ſo that that which in this caſe deſcends and is
placed in the water, is not only the Board of Ebony or Plate of Iron,

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