Galilei, Galileo - Discourse concerning the natation of bodies

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

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In lib: 1. of Na
tation of Bodies
Prop. 7.

Figure operates
not in the Nata
tion of Sollids.

It was anſwered me, that that proceeded not from the greater Levity;

but from the Figure, large and flat, which not being able to pene
trate the Reſiſtance of the Water, is the cauſe that it ſubmergeth not.
I replied, that any piece of Ice, of whatſoever Figure, ſwims upon
the Water, a manifeſt ſigne, that its being never ſo flat and broad,
hath not any part in its floating: and added, that it was a manifeſt
proofe hereof to ſee a piece of Ice of very broad Figure being thruſt
to the botome of the Water, ſuddenly return to flote atoppe, which
had it been more grave, and had its ſwimming proceeded from its
Forme, unable to penetrate the Reſiſtance of the Medium, that
would be altogether impoſſible; I concluded therefore, that the Figure
was in ſort a Cauſe of the Natation or Submerſion of Bodies,
but the greater or leſſe Gravity in reſpect of the Water: and there
fore all Bodyes heavier than it of what Figure ſoever they be, indiffe
rently go to the bottome, and the lighter, though of any figure, float
indifferently on the top: and I ſuppoſe that thoſe which hold other
wiſe, were induced to that beliefe, by ſeeing how that diverſity
of Formes or Figures, greatly altereth the Veloſity, and Tardity
of Motion; ſo that Bodies of Figure broad and thin, deſcend
far more leaſurely into the Water, than thoſe of a more compacted
Figure, though both made of the ſame Matter: by which ſome
might be induced to believe that the Dilatation of the Figure might
reduce it to ſuch ampleneſſe that it ſhould not only retard but wholly
impede and take away the Motion, which I hold to be falſe. Upon
this Concluſion, in many dayes diſcourſe, was ſpoken much, and
many things, and divers Experiments produced, of which your
Highneſſe heard, and ſaw ſome, and in this diſcourſe ſhall have
all that which hath been produced againſt my Aſſertion, and what
hath been ſuggeſted to my thoughts on this matter, and for con
firmation of my Concluſion: which if it ſhall ſuffice to remove that
(as I eſteem hitherto falſe) Opinion, I ſhall thinke I have not
unprofitably ſpent my paynes and time. and although that come
not to paſſe, yet ought I to promiſe another benefit to my ſelfe,
namely, of attaining the knowledge of the truth, by hearing my
Fallacyes confuted, and true demonſtrations produced by thoſe
of the contrary opinion.

And to proceed with the greateſt plainneſs and perſpicuity that
I can poſſible, it is, I conceive, neceſſary, firſt of all to declare
what is the true, intrinſecall, and totall Cauſe, of the aſcending of
ſome Sollid Bodyes in the Water, and therein floating; or on the
contrary, of their ſinking. and ſo much the rather in aſmuch as I
cannot ſatisfie my ſelfe in that which Ariſtotle hath left written on
this Subject.

The cauſe of the
Natation & ſub

I ſay then the Cauſe why ſome Sollid Bodyes deſcend to the

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