CONCERNING

_The Natation of BODIES Upon, or Submersion_

_In, the WATER._

Considering (Most Serene Prince) that the publishing this present

Treatise, of so different an Argument from that which many expect, and

which according to the intentions I proposed in my [A] Astronomicall

_Adviso_, I should before this time have put forth, might peradventure

make some thinke, either that I had wholly relinquished my farther

imployment about the new Celestiall Observations, or that, at least, I

handled them very remissely; I have judged fit to render an account,

aswell of my deferring that, as of my writing, and publishing this

treatise.

[A] His Nuncio Siderio.

As to the first, the last discoveries of _Saturn_ to be

tricorporeall, and of the mutations of Figure in _Venus_, like to

those that are seen in the Moon, together with the Consequents

depending thereupon, have not so much occasioned the demur, as the

investigation of the times of the Conversions of each of the Four

Medicean Planets about _Jupiter_, which I lighted upon in _April_ the

year past, 1611, at my being in _Rome_; where, in the end, I

assertained my selfe, that the first and neerest to _Jupiter_, moved

about 8 _gr._ & 29 _m._ of its Sphere in an houre, makeing its whole

revolution in one naturall day, and 18 hours, and almost an halfe. The

second moves in its Orbe 14 _gr._ 13 _min._ or very neer, in an hour,

and its compleat conversion is consummate in 3 dayes, 13 hours, and

one third, or thereabouts. The third passeth in an hour, 2 _gr._ 6

_min._ little more or less of its Circle, and measures it all in 7

dayes, 4 hours, or very neer. The fourth, and more remote than the

rest, goes in one houre, 0 _gr_ 54 _min._ and almost an halfe of its

Sphere, and finisheth it all in 16 dayes, and very neer 18 hours. But

because the excessive velocity of their returns or restitutions,

requires a most scrupulous precisenesse to calculate their places, in

times past and future, especially if the time be for many Moneths or

Years; I am therefore forced, with other Observations, and more exact

than the former, and in times more remote from one another, to correct

the Tables of such Motions, and limit them even to the shortest

moment: for such exactnesse my first Observations suffice not; not

only in regard of the short intervals of Time, but because I had not

as then found out a way to measure the distances between the said

Planets by any Instrument: I Observed such Intervals with simple

relation to the Diameter of the Body of _Jupiter_; taken, as we have

said, by the eye, the which, though they admit not errors of above a

Minute, yet they suffice not for the determination of the exact

greatness of the Spheres of those Stars. But now that I have hit upon

a way of taking such measures without failing, scarce in a very few

Seconds, I will continue the observation to the very occultation of

_JUPITER_, which shall serve to bring us to the perfect knowledge of

the Motions, and Magnitudes of the Orbes of the said Planets, together

also with some other consequences thence arising. I adde to these

things the observation of some obscure Spots[1], which are discovered in

the Solar Body, which changing, position in that, propounds to our

consideration a great argument either that the Sun revolves in it

selfe, or that perhaps other Starrs, in like manner as _Venus_ and

_Mercury_, revolve about it, invisible in other times, by reason of

their small digressions, lesse than that of _Mercury_, and only

visible when they interpose between the Sun and our eye, or else hint

the truth of both this and that; the certainty of which things ought

not to be contemned, nor omitted.

[1] The Authors Observations of the Solar Spots

_Continuall observation hath at last assured me that these Spots

are matters contiguous to the Body of the Sun, there continually

produced in great number, and afterwards dissolved, some in a

shorter, some in a longer time, and to be by the Conversion or

Revolution of the Sun in it selfe, which in a Lunar Moneth, or

thereabouts, finisheth its Period, caried about in a Circle, an

accident great of it selfe, and greater for its Consequences._

As to the other particular in the next place [B] Many causes have

moved me to write the present Tract, the subject whereof, is the

Dispute which I held some dayes since, with some learned men of this

City, about which, as your Highnesse knows, have followed many

Discourses: The principall of which Causes hath been the Intimation of

your Highnesse, having commended to me Writing, as a singular means to

make true known from false, reall from apparent Reasons, farr better

than by Disputing vocally, where the one or the other, or very often

both the Disputants, through too greate heate, or exalting of the

voyce, either are not understood, or else being transported by

ostentation of not yeilding to one another, farr from the first

Proposition, with the novelty, of the various Proposals, confound both

themselves and their Auditors.

[B] The occasion inducing the Author to write this Treatise.

Moreover, it seemed to me convenient to informe your Highnesse of all

the sequell, concerning the Controversie of which I treat, as it hath

been advertised often already by others: and because the Doctrine

which I follow, in the discussion of the point in hand, is different

from that of _Aristotle_; and interferes with his Principles, I have

considered that against the Authority of that most famous Man, which

amongst many makes all suspected that comes not from the Schooles of

the Peripateticks, its farr better to give ones Reasons by the Pen

than by word of mouth, and therfore I resolved to write the present

discourse: in which yet I hope to demonstrate that it was not out of

capritiousnesse, or for that I had not read or understood _Aristotle_,

that I sometimes swerve from his opinion, but because severall Reasons

perswade me to it, and the same _Aristotle_ hath tought me to fix my

judgment on that which is grounded upon Reason, and not on the bare

Authority of the Master[2]; and it is most certaine according to the

sentence of _Alcinoos_, that philosophating should be free. Nor is the

resolution of our Question in my judgment without some benefit to the

Universall[3], forasmuch as treating whether the figure of Solids

operates, or not, in their going, or not going to the bottome in

Water, in occurrences of building Bridges or other Fabricks on the

Water, which happen commonly in affairs of grand import, it may be of

great availe to know the truth.

[2] _Aristotle_ prefers Reason to the Authority ofan Author.

[3] The benefit of this Argument.

I say therfore, that being the last Summer in company with certain

Learned men, it was said in the argumentation; That Condensation was

the propriety of Cold[4], and there was alledged for instance, the

example of Ice: now I at that time said, that, in my judgment, the Ice

should be rather Water rarified than condensed[5], and my reason was,

because Condensation begets diminution of Mass, and augmentation of

gravity, and Rarifaction causeth greater Lightness, and augmentarion

of Masse: and Water in freezing, encreaseth in Masse, and the Ice made

thereby is lighter than the Water on which it swimmeth.

[4] Condensation the Propriety of Cold, according to the

Peripateticks.

[5] Ice rather water rarified, than condensed, and why:

_What I say, is manifest, because, the medium subtracting from the

whole Gravity of Sollids the weight of such another Masse of the

said Medium; as_ Archimedes _proves in his_ [C] First Booke De

Insidentibus Humido; _when ever the Masse of the said Solid

encreaseth by Distraction, the more shall the_ Medium _detract from

its entire Gravity; and lesse, when by Compression it shall be

condensed and reduced to a lesse Masse._

[C] In lib: 1. of Natation of Bodies Prop. 7.

[Sidenote: Figure operates not in the Natation of Sollids.]

It was answered me, tha{t} that proceeded not from the greater Levity,

but from the Figure, large and flat, which not being able to penetrate

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 therefore all Bodyes heavier than

it of what Figure soever they be, indifferently go to the bottome, and

the lighter, though of any figure, float indifferently on the top: and

I suppose that those which hold otherwise, 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 confirmation 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

myselfe in that which _Aristotle_ hath left written on this Subject.

[Sidenote: The cause of the Natation & submersion of Solids in

the Water.]

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

Water, is the excesse of their Gravity, above the Gravity of the

Water; and on the contrary, the excess of the Waters Gravity above the

Gravity of those, is the Cause that others do not descend, rather that

they rise from the Bottom, and ascend to the Surface. This was

subtilly demonstrated by _Archimedes_ in his Book Of the NATATION of

BODIES: Conferred afterwards by a very grave Author, but, if I erre

not invisibly, as below for defence of him, I shall endeavour to

prove.

I, with a different Method, and by other meanes, will endeavour to

demonstrate the same, reducing the Causes of such Effects to more

intrinsecall and immediate Principles, in which also are discovered

the Causes of some admirable and almost incredible Accidents, as that

would be, that a very little quantity of Water, should be able, with

its small weight, to raise and sustain a Solid Body, an hundred or a

thousand times heavier than it.

And because demonstrative Order so requires, I shall define certain

Termes, and afterwards explain some Propositions, of which, as of

things true and obvious, I may make use of to my present purpose.