An essay touching the gravitation, or non-gravitation of fluid bodies, and the reasons thereof

CHAP. VII.

Concerning the most probable solution of the Phaenomenon of the Non-Gravitation of Water in its fluid consistence.

IN matters controverted, though it be more easie to find faults with the suppositions of others, than to substitute such in their room as may be less capable of Ex∣ception; yet it is but just that (if it be possible) for every one that ex∣cepts against anothers supposition, should exhibit one of his own, that so he may run the same tryal with o∣thers, as others have done with him. And therefore in the former Chapter having (as near as I can understand them) propounded the

Solutions of other men, and laid them by, as seeming to me either inevident, or not giving a reasona∣ble account of the Probleme, I shall now exhibit my own Conjecture of the Reason of this Appearance in Nature, wishing it no better suc∣cess with others, than it deserves.

I have before premised, that 1. this question must not be under∣stood of a vessel of water, as the continens and res contenta make but one common Body, for so it is but in nature of a solid and not of a fluid body, and there is in that re∣spect no more consideration to be had of its fluidity, than if the wa∣ter in the vessel had been congeled into a whole Kegg of Ice; for the Kegg of Ice and the Water in the Bucket, together with the Bucket containing it; or the Water in the Bladder, together with the Blad∣der containing it, descend by one

simple line of Gravitation, perpen∣dicularly from its centre of Gra∣vity towards the centre of the Earth: but the question is touch∣ing the gravitation of the water in its fluid consistence, though con∣tained in the Ocean, or in a Tub or Bucket. 2. That I do not in this place contend against all Gravita∣tion of water, for possibly there may be some little allowed it, as un∣to Air, and especially by reason of the interspersions in the water (as likewise in the Air) of some small Atomes or Particles of terrestrial Matter, which may be heterogene∣ous to the nature of water as such, and as those Particles are in their gravity heavier than water, so they may accidentally cause a greater gravitation in the Particles of some water more than of other, as hath been before said.

But that which I contend for in

this place, is first, that the gravita∣tion of water in its fluid consisten∣cy, whether in the Sea or in a Bucket, if any at all, yet is so incon∣siderable, that it doth not conside∣rably press upon subjected bodies, nor incommodate Animals that live therein at any profundity, and not in the thousandth part in actu∣al gravitation proportionable to the weight of a Column of water commensurate in base to the subje∣cted body, and extending from the same to the superficies of the water. Secondly, to assign some reason of such Non-gravitation, and why it is not, no nor indeed can be.

The former of these is in effect confessed by all impartial Writers, and evident to every days experi∣ence. The latter therefore, name∣ly the reason thereof, are the subject of this Chapters inquiry.

And I think the reasons of this

Non-gravitation of the Particles of water upon such subjected bodies, are especially two. The first is Me∣chanical, from the structure of the fluid water; and the second is meer∣ly natural, from the nature of Flu∣ids. Touching the former of these, the Mechanical Solution of this Problem, this hath been in effect given before, in the Non-gravita∣tion of the parts of solid bodies while in Continuity, which it is plain though they all together gra∣vitate upon the Scale, yet one part doth not gravitate upon another: And water, though a fluid body, yet hath its continuity, which is undivided, and so gravitates not upon its own parts, nor upon any body within it of equal or greater weight than it self. But 2. admit, that water, in respect of its fluidity, should most participate of the na∣ture

or reason of solute and separa∣ble bodies, that are only contigu∣ous; yet even in those solute bo∣dies, as Sand, Granes, Shot, every Monad of such solute bodies gives support to the superjacent Particles, though not united into one continu∣um, as in the instances of a Pyramid of square Stones, a heap of Wheat, or of Callice Sand; wherein a kind of Arch is made over the subjected bodies, that they by no means su∣stain the whole weight of the in∣cumbent column, proportionate to the base of the body included.

But in case of the body of water, the same advantage is infinitely more improveable for the ease and security of the subjacent bodies, whether animate or not. For al∣though I shall not take advantage of the imaginary configuration of the Particles of water invented by des Cartes, who supposeth them to

be like small oblong filaments or fibres, not much unlike little Grigs or Eels, which would easily make a consistency, that like an Arch would protect and cover the subja∣cent body. Nevertheless I shall say this, that the union of its parts are much closer than that of the Monads of Callice sand, for the water is quid continuum, though fluidum; & therefore as the parts of one conti∣nued solid body do not gravitate upon the other parts, but only upon the common base of the whole bo∣dy; so the parts of water do not gravitate upon themselves, nor up∣on any particular base less than their own base, but one part su∣stains the other without any gravi∣tation: as the Arch of a well fra∣med Vault, doth not press upon the subjected Vault, but each part is sustained by the other, and the whole by those walls from whence

the Ribs of the Arch are drawn. A very little industrious trial of the suspension of Sand in a Tube fra∣med for that purpose, will make the Instance more intelligible, than words or writing can do it.

It may possibly be true, that a more broad body, heavier than so much quantity of water, may have a greater gravitation of water up∣on it than a narrower, because the arch that is made over it by the wa∣ter, is greater than that Arch that is made over the narrower body. For instance, let us suppose that in the bottom of a Bucket of water, three foot deep, and one foot in the circumference, there be placed an Ebony rundle, of one Inch thick, and eight Inches Diameter; and in the bottom of the like Bucket there be placed a rundle of Ebony of four Inches Diameter, and of such a thickness as may make the

weight of it equal to the weight of the greater rundle, as in the subje∣cted Figures.

[illustration]

I say it may fall out, that the wa∣ter may more gravitate upon the greater Rundle, than upon the les∣ser, because that small Cone of wa∣ter that is incumbent upon the greater, which hath the larger base, makes a larger Conical body of wa∣ter upon that which hath the lar∣ger basis, than that which hath the narrower. This may be easily tried by a pair of Scales, industriously or∣dered for such an Experiment. But however that fall out, it is most evident, that the whole weight of the column of water, commensu∣rate to the base of either Rundle,

and extending it self to the superfi∣cies of the water, doth not in its full weight gravitate upon either, un∣less we suppose a hole in the bot∣tom of the Vessel under either Run∣dle, and then indeed the water will gravitate upon the Rundle, because it gravitates upon the hole.

But if the subjected body be lighter than the like quantity of water, commensurable to its bulk, then it is true the water will un∣dermine that lighter body, and car∣ry it to the superficies, notwithstan∣ding the superimpendent Cone or Column of water: but this is not to my present purpose to explicate, and therefore I leave it.