_One of the above named Solids, when more grave_ in specie _than the
water, can never be sustained, by any whatever quantity of it._
For having seen how that the Moment wherewith such a Solid, as grave
_in specie_ as the water, contrasts with the Moment of any Mass of
water whatsoever, is able to retain it, even to its totall Submersion,
without its ever ascending; it remaineth, manifest, that the water is
far less able to raise it up, when it exceeds the same _in specie_:
so, that though you infuse water till its totall Submersion, it shall
still stay at the Bottome, and with such Gravity, and Resistance to
Elevation, as is the excess of its Absolute Gravity, above the
Absolute Gravity of a Mass equall to it, made of water, or of a Matter
_in specie_ equally grave with the water: and, though you should
moreover adde never so much water above the Levell of that which
equalizeth the Altitude of the Solid, it shall not, for all that,
encrease the Pression, or Gravitation, of the parts circumfused about
the said Solid, by which greater pression, it might come to be
repulsed; because, the Resistance is not made, but only by those parts
of the water, which at the Motion of the said Solid do also move, and
these are those only, which are comprehended by the two Superficies
equidistant to the Horizon, and their parallels, that comprehend the
Altitude of the Solid immerged in the water.
I conceive, I have by this time sufficiently declared and opened the
way to the contemplation of the true, intrinsecall and proper Causes
of diverse Motions, and of the Rest of many Solid Bodies in diverse
_Mediums_, and particularly in the water, shewing how all in effect,
depend on the mutuall excesses of the Gravity of the Moveables and of
the _Mediums_: and, that which did highly import, removing the
Objection, which peradventure would have begotten much doubting, and
scruple in some, about the verity of my Conclusion, namely, how that
notwithstanding, that the excess of the Gravity of the water, above
the Gravity of the Solid, demitted into it, be the cause of its
floating and rising from the Bottom to the Surface, yet a quantity of
water, that weighs not ten pounds, can raise a Solid that weighs above
100 pounds: in that we have demonstrated, That it sufficeth, that such
difference be found between the Specificall Gravities of the _Mediums_
and Moveables, let the particular and absolute Gravities be what they
will: insomuch, that a Solid, provided that it be Specifically less
grave than the water, although its absolute weight were 1000 pounds,
yet may it be born up and elevated by ten pounds of water, and less:
and on the contrary, another Solid, so that it be Specifically more
grave than the water, though in absolute Gravity it were not above a
pound, yet all the water in the Sea, cannot raise it from the Bottom,
or float it. This sufficeth me, for my present occasion, to have, by
the above declared Examples, discovered and demonstrated, without
extending such matters farther, and, as I might have done, into a long
Treatise: yea, but that there was a necessity of resolving the above
proposed doubt, I should have contented my self with that only, which
is demonstrated by _Archimedes_, in his first _Book De Insidentibus
humido_[14]: where in generall termes he infers and confirms the same
Conclusions, namely, that Solids (_a_) less grave than water, swim or
float upon it, the (_b_) more grave go to the Bottom, and the (_c_)
equally grave rest indifferently in all places, yea, though they
should be wholly under water.
[14] _Of Natation_ (a) _Lib. 1, Prop. 4._ (b) _Id. Lib. 1. Prop.
3._ (c) _Id. Lib. 1. Prop. 3._
[Sidenote: The Authors defence of _Archimedes_ his Doctrine,
against the oppositions of _Buonamico_.]
But, because that this Doctrine of Archimedes, perused, transcribed
and examined by _Signor Francesco Buonamico_, in his _fifth Book of
Motion, Chap. 29_, and afterwards by him confuted, might by the
Authority of so renowned, and famous a Philosopher, be rendered
dubious, and suspected of falsity; I have judged it necessary to
defend it, if I am able so to do, and to clear _Archimedes_, from
those censures, with which he appeareth to be charged. _Buonamico_
rejecteth the Doctrine of _Archimedes_, first[15], as not consentaneous
with the Opinion of _Aristotle_, adding, that it was a strange thing
to him, that the Water should exceed the Earth in Gravity[16], seeing on
the contrary, that the Gravity of water, increaseth, by means of the
participation of Earth. And he subjoyns presently after[17], that he was
not satisfied with the Reasons of _Archimedes_, as not being able with
that Doctrine, to assign the cause whence it comes, that a Boat and a
Vessell, which otherwise, floats above the water, doth sink to the
Bottom, if once it be filled with water; that by reason of the
equality of Gravity, between the water within it, and the other water
without, it should stay a top; but yet, nevertheless, we see it to go
to the Bottom.
[15] His first Objection against the Doctrine of _Archimedes_.
[16] His Second Objection.
[17] His third Objection.
He farther addes[18], that _Aristotle_ had clearly confuted the Ancients,
who said, that light Bodies moved upwards[19], driven by the impulse of
the more grave Ambient: which if it were so, it should seem of
necessity to follow, that all naturall Bodies are by nature heavy, and
none light: For that the same would befall the Fire and Air, if put in
the Bottom of the water. And, howbeit, _Aristotle_ grants a Pulsion in
the Elements, by which the Earth is reduced into a Sphericall Figure,
yet nevertheless, in his judgement; it is not such that it can remove
grave Bodies from their naturall places, but rather, that it send them
toward the Centre, to which (as he somewhat obscurely continues to
say,) the water principally moves, if it in the interim meet not with
something that resists it, and, by its Gravity, thrusts it out of its
place: in which case, if it cannot directly, yet at least as well as
it can, it tends to the Centre: but it happens, that light Bodies by
such Impulsion, do all ascend upward: but this properly they have by
nature, as also, that other of swimming. He concludes, lastly[20], that he
concurs with _Archimedes_ in his Conclusions; but not in the Causes,
which he would referre to the facile and difficult Separation of the
_Medium_, and to the predominance of the Elements, so that when the
Moveable superates the power of the _Medium_; as for example, Lead
doth the Continuity of water, it shall move thorow it, else not.
[18] His fourth Objection.
[19] The _A_ncients denyed _A_bsolute Levity.
[20] The causes of Natation & Submersion, according to the
Peripateticks.
This is all that I have been able to collect, as produced against
_Archimedes_ by _Signor Buonamico_: who hath not well observed the
Principles and Suppositions of _Archimedes_; which yet must be false,
if the Doctrine be false, which depends upon them; but is contented to
alledge therein some Inconveniences, and some Repugnances to the
Doctrine and Opinion of _Aristotle_. In answer to which Objections, I
say, first[21], That the being of _Archimedes_ Doctrine, simply different
from the Doctrine of _Aristotle_, ought not to move any to suspect it,
there being no cause, why the Authority of this should be preferred to
the Authority of the other: but, because, where the decrees of Nature
are indifferently exposed to the intellectuall eyes of each, the
Authority of the one and the other, loseth all a{u}thenticalness of
Perswasion, the absolute power residing in Reason; therefore I pass to
that which he alledgeth in the second place[22], as an absurd consequent
of the Doctrine of _Archimedes_, namely, That water should be more
grave than Earth. But I really find not, that ever _Archimedes_ said
such a thing, or that it can be rationally deduced from his
Conclusions: and if that were manifest unto me, I verily believe, I
should renounce his Doctrine, as most erroneous. Perhaps this
Deduction of _Buonamico_, is founded upon that which he citeth of the
Vessel, which swims as long as its voyd of water, but once full it
sinks to the Bottom, and understanding it of a Vessel of Earth, he
infers against _Archimedes_ thus: Thou sayst that the Solids which
swim, are less grave than water: this Vessell swimmeth: therefore,
this Vessell is lesse grave than water. If this be the Illation. I
easily answer, granting that this Vessell is lesse grave than water,
and denying the other consequence, namely, that Earth is less Grave
than Water. The Vessel that swims occupieth in the water, not only a
place equall to the Mass of the Earth, of which it is formed; but
equall to the Earth and to the Air together, contained in its
concavity. And, if such a Mass compounded of Earth and Air, shall be
less grave than such another quantity of water, it shall swim, and
shall accord with the Doctrine of _Archimedes_; but if, again,
removing the Air, the Vessell shall be filled with water, so that the
Solid put in the water, be nothing but Earth, nor occupieth other
place, than that which is only possest by Earth, it shall then go to
the Bottom, by reason that the Earth is heavier than the water: and
this corresponds well with the meaning of _Archimedes_. See the same
effect illustrated, with such another Experiment, In pressing a Viall
Glass to the Bottom of the water, when it is full of Air, it will meet
with great resistance, because it is not the Glass alone, that is
pressed under water, but together with the Glass a great Mass of Air,
and such, that if you should take as much water, as the Mass of the
Glass, and of the Air contained in it, you would have a weight much
greater than that of the Viall, and of its Air: and, therefore, it
will not submerge without great violence: but if we demit only the
Glass into the water, which shall be when you shall fill the Glass
with water, then shall the Glass descend to the Bottom; as superiour
in Gravity to the water.
[21] The Authors answer to the first Objection.
[22] The Authors answer to the second Objection.
Returning, therefore, to our first purpose; I say, that Earth is more
grave than water, and that therefore, a Solid of Earth goeth to the
bottom of it; but one may possibly make a composition of Earth and
Air, which shall be less grave than a like Mass of Water; and this
shall swim: and yet both this and the other experiment shall very well
accord with the Doctrine of _Archimedes_. But because that in my
judgment it hath nothing of difficulty in it, I will not positively
affirme that _Signor Buonamico_, would by such a discourse object unto
_Archimedes_ the absurdity of inferring by his doctrine, that Earth
was less grave than Water, though I know not how to conceive what
other accident he could have induced thence.
Perhaps such a Probleme (in my judgement false) was read by _Signor
Buonamico_ in some other Author, by whom peradventure it was
attributed as a singular propertie, of some particular Water, and so
comes now to be used with a double errour in confutation of
_Archimedes_, since he saith no such thing, nor by him that did say it
was it meant of the common Element of Water.
[Sidenote: The Authors answer to the third Objection.]
The third difficulty in the doctrine of _Archimedes_ was, that he
could not render a reason whence it arose, that a piece of Wood, and a
Vessell of Wood, which otherwise floats, goeth to the bottom, if
filled with Water. _Signor Buonamico_ hath supposed that a Vessell of
Wood, and of Wood that by nature swims, as before is said, goes to the
bottom, if it be filled with water; of which he in the following
Chapter, which is the 30 of the fifth Book copiously discourseth: but
I (speaking alwayes without diminution of his singular Learning) dare
in defence of _Archimedes_ deny this experiment, being certain that a
piece of Wood which by its nature sinks not in Water, shall not sinke
though it be turned and converted into the forme of any Vessell
whatsoever, and then filled with Water: and he that would readily see
the Experiment in some other tractable Matter, and that is easily
reduced into several Figures, may take pure Wax, and making it first
into a Ball or other solid Figure, let him adde to it so much Lead as
shall just carry it to the bottome, so that being a graine less it
could not be able to sinke it, and making it afterwards into the forme
of a Dish, and filling it with Water, he shall finde that without the
said Lead it shall not sinke, and that with the Lead it shall descend
with much slowness: & in short he shall satisfie himself, that the
Water included makes no alteration. I say not all this while, but that
its possible of Wood to make Barkes, which being filled with water,
sinke; but that proceeds not through its Gravity, encreased by the
Water, but rather from the Nailes and other Iron Workes, so that it no
longer hath a Body less grave than Water, but one mixt of Iron and
Wood, more grave than a like Masse of Water. Therefore let _Signor
Buonamico_ desist from desiring a reason of an effect, that is not in
nature: yea if the sinking of the Woodden Vessell when its full of
Water, may call in question the Doctrine of _Archimedes_, which he
would not have you to follow, is on the contrary consonant and
agreeable to the Doctrine of the Peripateticks, since it aptly
assignes a reason why such a Vessell must, when its full of Water,
descend to the bottom; converting the Argument the other way, we may
with safety say that the Doctrine of _Archimedes_ is true, since it
aptly agreeth with true experiments, and question the other, whose
Deductions are fastened upon erroneouss Conclusions. As for the other
point hinted in this same Instance, where it seemes that _Benonamico_
understands the same not only of a piece of wood, shaped in the forme
of a Vessell, but also of massie Wood, which filled, _scilicet_, as I
believe, he would say, soaked and steeped in Water, goes finally to
the bottom that happens in some porose Woods, which, while their
Porosity is replenished with Air, or other Matter less grave than
Water, are Masses specificially less grave than the said Water, like
as is that Viall of Glass whilest it is full of Air: but when, such
light Matter departing, there succeedeth Water into the same
Porosities and Cavities, there results a compound of Water and Glass
more grave than a like Mass of Water: but the excess of its Gravity
consists in the Matter of the Glass, and not in the Water, which
cannot be graver than it self: so that which remaines of the Wood, the
Air of its Cavities departing, if it shall be more grave _in specie_
than Water, fil but its Porosities with Water, and you shall have a
Compost of Water and of Wood more grave than Water, but not by vertue
of the Water received into and imbibed by the Porosities, but of that
Matter of the Wood which remains when the Air is departed: and being
such it shall, according to the Doctrine of _Archimedes_, goe to the
bottom, like as before, according to the same Doctrine it did swim.
[Sidenote: The Authors answer to the fourth Objection.]
As to that finally which presents itself in the fourth place,
namely, that the _Ancients_ have been heretofore confuted by
_Aristotle_, who denying Positive and Absolute Levity, and truely
esteeming all Bodies to be grave, said, that that which moved upward
was driven by the circumambient Air, and therefore that also the
Doctrine of _Archimedes_, as an adherent to such an Opinion was
convicted and confuted: I answer first, that _Signor Buonamico_ in my
judgement hath imposed upon _Archimedes_, and deduced from his words
more than ever he intended by them, or may from his Propositions be
collected, in regard that _Archimedes_ neither denies, nor admitteth
Positive Levity, nor doth he so much as mention it: so that much less
ought _Buonamico_ to inferre, that he hath denyed that it might be the
Cause and Principle of the Ascension of Fire, and other Light Bodies[23]:
having but only demonstrated, that Solid Bodies more grave than Water
descend in it, according to the excess of their Gravity above the
Gravity of that, he demonstrates likewise, how the less grave ascend
in the same Water[24], accordng to its excess of Gravity, above the
Gravity of them. So that the most that can be gathered from the
Demonstration of _Archimedes_ is, that like as the excess of the
Gravity of the Moveable above the Gravity of the Water, is the Cause
that it descends therein, so the excess of the Gravity of the water
above that of the Moveable, is a sufficient Cause why it descends not,
but rather betakes it self to swim: not enquiring whether of moving
upwards there is, or is not any other Cause contrary to Gravity: nor
doth _Archimedes_ discourse less properly than if one should say: If
the South Winde shall assault the Barke with greater _Impetus_ than is
the violence with which the Streame of the River carries it towards
the South, the motion of it shall be towards the North: but if the
_Impetus_ of the Water shall overcome that of the Winde, its motion
shall be towards the South. The discourse is excellent and would be
unworthily contradicted by such as should oppose it, saying: Thou
mis-alledgest as Cause of the motion of the Bark towards the South,
the _Impetus_ of the Stream of the Water above that of the South
Winde; mis-alledgest I say, for it is the Force of the North Winde
opposite to the South, that is able to drive the Bark towards the
South. Such an Objection would be superfluous, because he which
alledgeth for Cause of the Motion the Stream of the Water, denies not
but that the Winde opposite to the South may do the same, but only
affirmeth that the force of the Water prevailing over the South Wind,
the Bark shall move towards the South: and saith no more than is true.
And just thus when _Archimedes_ saith, that the Gravity of the Water
prevailing over that by which the moveable descends to the Bottom,
such moveable shall be raised from the Bottom to the Surface alledgeth
a very true Cause of such an Accident, nor doth he affirm or deny that
there is, or is not, a vertue contrary to Gravity, called by some
Levity, that hath also a power of moving some Matters upwards. Let
therefore the Weapons of _Signor Buonamico_ be directed against
_Plato_[25], and other _Ancients_, who totally denying _Levity_, and
taking all Bodies to be grave, say that the Motion upwards is made,
not from an intrinsecal Principle of the Moveable, but only by the
Impulse of the _Medium_; and let _Archimedes_ and his Doctrine escape
him, since he hath given him no Cause of quarelling with him. But if
this Apologie, produced in defence of _Archimedes_, should seem to
some insufficient to free him from the Objections and Arguments,
produced by _Aristotle_ against _Plato_, and the other _Ancients_, as if
they did also fight against _Archimedes_, alledging the Impulse of the
Water as the Cause of the swimming of some Bodies less grave than it[26],
I would not question, but that I should be able to maintaine the
Doctrine of _Plato_ and those others to be most true, who absolutely
deny Levity, and affirm no other Intrinsecal Principle of Motion to be
in Elementary Bodies save only that towards the Centre of the Earth[27],
nor no other Cause of moving upwards, speaking of that which hath the
resemblance of natural Motion, but only the repulse of the _Medium_,
fluid, and exceeding the Gravity of the Moveable[28]: and as to the
Reasons of _Aristotle_ on the contrary, I believe that I could be able
fully to answer them, and I would assay to do it, if it were
absolutely necessary to the present Matter, or were it not too long a
Digression for this short Treatise. I will only say, that if there
were in some of our Ellementary Bodies an Intrinsecall Principle and
Naturall Inclination to shun the Centre of the Earth, and to move
towards the Concave of the Moon, such Bodies, without doubt, would
more swiftly ascend through those _Mediums_ that least oppose the
Velocity of the Moveable, and these are the more tenuous and subtle;
as is, for example, the Air in comparison of the Water, we daily
proving that we can with farre more expeditious Velocity move a Hand
or a Board to and again in one than in the other[29]: nevertheless, we
never could finde any Body, that did not ascend much more swiftly in
the water than in the Air. Yea of Bodies which we see continually to
ascend in the Water, there is none that having arrived to the confines
of the Air, do not wholly lose their Motion[30]; even the Air it self,
which rising with great Celerity through the Water, being once come to
its Region it loseth all
[23] Of Natation, Lib. 1. Prop. 7.
[24] Of Natation, Lib. 1. Prop. 4.
[25] _Plato_ denyeth Positive Levity.
[26] The Authors defence of the doctrine of _Plato_ and the
_Ancients_, who absolutely deny Levity:
[27] According to _Plato_ there is no Principle of the Motion, of
descent in Naturall Bodies, save that to the Centre.
[28] No cause of the motion of Ascent, save the Impulse of the
_Medium_, exceeding the Moveable in Gravitie.
[29] Bodies ascend much swifter in the Water, than in the Air.
[30] All Bodies ascending through Water, lose their Motion,
comming to the confines of the Air.
[Sidenote: The lighter Bodies ascend more swiftly through Water.]
And, howbeit, Experience shewes, that the Bodies, successively less
grave, do most expeditiously ascend in water, it cannot be doubted,
but that the Ignean Exhalations do ascend more swiftly through the
water, than doth the Air: which Air is seen by Experience to ascend
more swiftly through the Water, than the Fiery Exhalations through the
Air[31]: Therefore, we must of necessity conclude, that the said
Exhalations do much more expeditiously ascend through the Water, than
through the Air; and that, consequently, they are moved by the Impulse
of the Ambient _Medium_, and not by an intrinsick Principle that is in
them, of avoiding the Centre of the Earth; to which other grave Bodies
tend.
[31] Fiery Exhalations ascend thorow the Water more swiftly than
doth the Air; & the Air ascends more swiftly thorow the Water,
than Fire thorow the Air.
[Sidenote: _T_he Authors confutation of the Peripateticks Causes
of Natation & Submersion.]
To that which for a finall conclusion, _Signor Buonamico_ produceth
of going about to reduce the descending or not descending, to the
easie and uneasie Division of the _Medium_, and to the predominancy of
the Elements: I answer, as to the first part, that that cannot in any
manner be admitted as a Cause, being that in none of the Fluid
_Mediums_, as the Air, the Water, and other Liquids, there is any
Resistance against Division[32], but all by every the least Force, are
divided and penetrated, as I will anon demonstrate: so, that of such
Resistance of Division there can be no Act, since it self is not in
being. As to the other part, I say, that the predominancy of the
Elements in Moveables[33], is to be considered, as far as to the excesse
or defect of Gravity, in relation to the _Medium_: for in that Action,
the Elements operate not, but only, so far as they are grave or light:
therefore, to say that the Wood of the Firre sinks not, because Air
predominateth in it, is no more than to say, because it is less grave
than the Water. Yea, even the immediate Cause, is its being less grave
than the Water[34]: and it being under the predominancy of the Air, is the
Cause of its less Gravity: Therefore, he that alledgeth the
predominancy of the Element for a Cause, brings the Cause of the
Cause, and not the neerest and immediate Cause. Now, who knows not
that the true Cause is the immediate, and not the mediate[35]? Moreover,
he that alledgeth Gravity, brings a Cause most perspicuous to Sence[36]:
The cause we may very easily assertain our selves; whether Ebony, for
example, and Firre, be more or less grave than water: but whether
Earth or Air predominates in them, who shall make that manifest?
Certainly, no Experiment can better do it than to observe whether they
swim or sink. So, that he who knows, not whether such a Solid swims,
unless when he knows that Air predominates in it, knows not whether it
swim, unless he sees it swim, for then he knows that it swims, when he
knows that it is Air that predominates, but knows not that Air hath
the predominance, unless he sees it swim: therefore, he knows not if
it swims, till such time as he hath seen it swim.
[32] Water & other fluids void of Resistance against Division.
[33] _T_he predominancy of Elements in Moveables to be considered
only in relation to their excess or defect of Gravity in reference
to the _Medium_.
[34] _T_he immediate Cause of Natation is that the Moveable is
less grave than the Water.
[35] _T_he Peripateticks alledge for the reason of Natation the
Cause of the Cause.
[36] Gravity a Cause most perspicuous to sence.
Let us not then despise those Hints, though very dark, which Reason,
after some contemplation, offereth to our Intelligence, and lets be
content to be taught by _Archimedes_, that then any Body shall
submerge in water[37], when it shall be specifically more grave than it,
and that if it shall be less grave[38], it shall of necessity swim, and
that it will rest indifferently in any place under water, if its
Gravity be perfectly like to that of the water.
[37] Lib 1. of Natation Prop. 7
[38] Id. Lib. 1. Prop. 4.
These things explained and proved[39], I come to consider that which
offers it self, touching what the Diversity of figure given unto the
said Moveable hath to do with these Motions and Rests; and proceed to
affirme, that,
[39] Id. Lib 1. Prop. 3.