Discourse on Floating Bodies Part 3

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 Frances...o...b..onamico_, 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 partic.i.p.ation 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 a.s.sign 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 princ.i.p.ally 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 pa.s.s 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 Ma.s.s 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 Ma.s.s compounded of Earth and Air, shall be less grave than such another quant.i.ty 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 ill.u.s.trated, with such another Experiment, In pressing a Viall Gla.s.s to the Bottom of the water, when it is full of Air, it will meet with great resistance, because it is not the Gla.s.s alone, that is pressed under water, but together with the Gla.s.s a great Ma.s.s of Air, and such, that if you should take as much water, as the Ma.s.s of the Gla.s.s, 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 Gla.s.s into the water, which shall be when you shall fill the Gla.s.s with water, then shall the Gla.s.s 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 Ma.s.s 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 Ma.s.se 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 a.s.signes 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 ma.s.sie 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 Ma.s.ses specificially less grave than the said Water, like as is that Viall of Gla.s.s 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 Gla.s.s more grave than a like Ma.s.s of Water: but the excess of its Gravity consists in the Matter of the Gla.s.s, 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 circ.u.mambient 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 a.s.sault 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 a.s.say 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 a.s.sertain 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.

THEOREME V.

[Sidenote: Diversity of Figure no Cause of its absolute Natation or Submersion.]

_The diversity of Figures given to this or that Solid, cannot any way be a Cause of its absolute Sinking or Swimming._

So that if a Solid being formed, for example, into a Sphericall Figure, doth sink or swim in the water, I say, that being formed into any other Figure, the same figure in the same water, shall sink or swim: nor can such its Motion by the Expansion or by other mutation of Figure, be impeded or taken away.

[Sidenote: The Expansion of Figure, r.e.t.a.r.ds the Velocity of the ascent or descent of the Moveable in the water; but doth not deprive it of all Motion.]