Chapter 6

And that we may the better finde what the _cause_ of _Congruity_ and _Incongruity_ in bodies is, it will be requisite to consider, First, what is the _cause_ of _fluidness_; And this, _I conceive_, to be nothing else but a certain _pulse_ or _shake_ of _heat_; for Heat being nothing else but a very _brisk_ and _vehement agitation_ of the parts of a body (as I have elswhere made _probable_) the parts of a body are thereby made so _loose_ from one another, that they easily _move any way_, and become _fluid_. That I may explain this a little by a gross Similitude, let us suppose a dish of sand set upon some body that is very much _agitated_, and shaken with some _quick_ and _strong vibrating motion_, as on a _Milstone_ turn’d round upon the under stone very violently whilst it is empty; or on a very stiff _Drum_-head, which is vehemently or very nimbly beaten with the Drumsticks. By this means, the sand in the dish, which before lay like a _dull_ and unactive body, becomes a perfect _fluid_; and ye can no sooner make a _hole_ in it with your finger, but it is immediately _filled up again_, and the upper surface of it _levell’d_. Nor can you _bury_ a _light body_, as a piece of Cork under it, but it presently _emerges_ or _swims_ as ’twere on the top; nor can you lay a _heavier_ on the top of it, as a piece of Lead, but it is immediately _buried_ in Sand, and (as ’twere) sinks to the bottom. Nor can you make a _hole_ in the side of the Dish, but the sand shall _run out_ of it to a _level_, not an _obvious property_ of a fluid body, as such, but this dos _imitate_; and all this meerly caused by the vehement _agitation_ of the conteining vessel; for by this means, _each_ sand becomes to have a _vibrative_ or _dancing_ motion, so as no other heavier body can _rest_ on it, unless _sustein’d_ by some other on either side: Nor will it suffer any Body to be _beneath_ it, unless it be a _heavier_ then it self. Another Instance of the strange _loosening_ nature of a violent jarring Motion, or a strong and nimble vibrative one, we may have from a piece of _iron_ grated on very strongly with a _file_: for if into that a pin _screw’d_ so firm and hard, that though it has a convenient head to it, yet it can by no means be _unscrew’d_ by the fingers; if, I say, you attempt to unscrew this whilst _grated on by the file_, it will be found to undoe and turn very _easily_. The first of these Examples manifests, how a body actually _divided_ into small parts, becomes a _fluid_. And the latter manifests by what means the agitation of heat so easily _loosens_ and _unties_ the parts of _solid_ and _firm_ bodies. Nor need we suppose heat to be any thing else, besides such a motion; for supposing we could _Mechanically_ produce such a one _quick_ and _strong_ enough, we need not spend _fuel_ to _melt_ a body. Now, that I do not speak this altogether groundless, I must refer the Reader to the Observations I have made upon the shining sparks of Steel, for there he shall find that _the same_ effects are produced upon small chips or parcels of Steel by the _flame_, and by _a quick and violent motion_; and if the body of _steel_ may be thus melted (as I there shew it may) I think we have little reason to doubt that almost _any other_ may not also. Every Smith can inform one how quickly both his _File_ and the _Iron_ grows _hot_ with _filing_, and if you _rub_ almost any two _hard_ bodies together, they will do the same: And we know, that a sufficient degree of heat causes _fluidity_, in some bodies much sooner, and in others later; that is, the parts of the body of some are so _loose_ from one another, and so _unapt to cohere_, and so _minute_ and _little_, that a very _small_ degree of agitation keeps them always in the _state of fluidity_. Of this kind, I suppose, the _Æther_, that is the _medium_ or _fluid_ body, in which all other bodies do as it were swim and move; and particularly, the _Air_, which seems nothing else but a kind of _tincture_ or _solution_ of terrestrial and aqueous particles _dissolv’d_ into it, and agitated by it, just as the _tincture_ of _Cocheneel_ is nothing but some finer _dissoluble_ parts of that Concrete lick’d up or _dissolv’d_ by the _fluid_ water. And from this Notion of it, we may easily give a more Intelligible reason how the Air becomes so capable of _Rarefaction_ and _Condensation_. For, as in _tinctures_, one grain of some _strongly tinging_ substance may _sensibly_ colour some _hundred thousand_ grains of _appropriated_ Liquors, so as every _drop_ of it has its proportionate share, and be sensibly ting’d, as I have try’d both with _Logwood_ and _Cocheneel_: And as some few grains of _Salt_ is able to infect as great a quantity, as may be found by _præcipitations_, though not so easily by the _sight_ or _taste_; so the _Air_, which seems to be but as ’twere a _tincture_ or _saline substance, dissolv’d and agitated by the fluid and agil Æther_, may disperse and _expand_ it self into a _vast space_, if it have room enough, and infect, as it were, every part of that space. But, as on the other side, if there be but some _few grains_ of the liquor, it may _extract all_ the colour of the tinging substance, and may _dissolve_ all the Salt, and thereby become _much more impregnated_ with those substances, so may _all_ the air that sufficed in a _rarify’d state_ to fill some _hundred thousand_ spaces of Æther, be compris’d in only _one_, but in a position proportionable _dense_. And though we have not yet found out such _strainers_ for Tinctures and Salts as we have for the Air, being yet unable to _separate_ them from their dissolving liquors by any kind of _filtre_, without _præcipitation_, as we are able to _separate_ the Air from the Æther by _Glass_, and several other bodies. And though we are yet unable and ignorant of the ways of _præcipitating_ Air out of the Æther as we can Tinctures, and Salts out of several _dissolvents_; yet neither of these seeming _impossible_ from the nature of the things, nor so _improbable_ but that some happy future industry may find out ways to effect them; nay, further, since we find that Nature _does really perform_ (though by what means we are not certain) both these actions, namely, by _præcipitating_ the Air in Rain and Dews, and by supplying the Streams and Rivers of the World with fresh water, _strain’d_ through secret subterraneous Caverns: And since, that in very many other _proprieties_ they do so exactly _seem_ of the _same nature_; till further observations or tryals do inform us of the _contrary_, we may _safely enough conclude_ them of the _same kind_. For it seldom happens that any two natures have so many properties _coincident_ or the _same_, as I have observ’d Solutions and Air to have, and to be _different_ in the rest. And therefore I think it neither _impossible_, _irrational_, nay nor _difficult_ to be able to _predict_ what is _likely_ to happen in other particulars also, besides those which _Observation_ or _Experiment_ have declared thus or thus; especially, if the _circumstances_ that do often very much conduce to the variation of the effects be duly _weigh’d_ and _consider’d_. And indeed, were there not a _probability_ of this, our _inquiries_ would be _endless_, our _tryals vain_, and our greatest _inventions_ would be nothing but the meer _products_ of _chance_, and not of _Reason_; and, like _Mariners_ in an Ocean, destitute both of a _Compass_ and the sight of the _Celestial guides_, we might indeed, _by chance_, Steer _directly_ towards our desired Port, but ’tis _a thousand to one_ but we _miss_ our aim. But to proceed, we may hence also give a plain reason, how the Air comes to be _darkned_ by _clouds_, &c. which are nothing but a kind of _precipitation_, and how those _precipitations_ fall down in _Showrs_. Hence also could I very easily, and I think truly, deduce the cause of the curious _sixangular figures_ of Snow, and the appearances of _Haloes, &c._ and the sudden _thickning_ of the Sky with Clouds, and the _vanishing_ and _disappearing_ of those Clouds again; for all these things may be very easily _imitated_ in a _glass of liquor_, with some slight _Chymical preparations_ as I have often try’d, and may somewhere else more largely relate, but have not now time to set them down. But to proceed, there are other bodies that consist of particles more _Gross_, and of a more _apt_ figure for _cohesion_, and this requires _somewhat greater_ agitation; such, I suppose ☿, _fermented vinous_ _Spirits_, several _Chymical Oils_, which are much of kin to those Spirits, &c. Others yet require a _greater_, as _water_, and so others _much greater_, for almost infinite degrees: For, I suppose there are very _few_ bodies in the world that may not be made _aliquatenus_ fluid, by _some_ or _other_ degree of agitation or heat.

Having therefore in short set down my Notion of a Fluid body, I come in the next place to consider what _Congruity_ is; and this, as I said before, being a _Relative property_ of a fluid, whereby it may be said to be _like_ or _unlike_ to this or that other body, whereby it _does_ or _does not mix_ with this or that body. We will again have recourse to our former Experiment, though but a rude one; and here if we mix in the dish _several kinds_ of sands, some of _bigger_, others of _less_ and finer bulks, we shall find that by the agitation _the fine sand_ will _eject_ and _throw out_ of it self all those _bigger_ bulks of small _stones_ and the like, and those will _be gathered_ together all into _one_ place; and if there be _other_ bodies in it of other natures, those also will be _separated_ into a place by themselves, and _united_ or _tumbled_ up together. And though this do not come up to the _highest property_ of _Congruity_, which is a _Cohæsion_ of the parts of the fluid together, or a kind of _attraction_ and _tenacity_, yet this does as ’twere _shadow_ it out, and somewhat resemble it; for just after the same manner, I suppose the _pulse_ of heat to _agitate_ the small parcels of matter, and those that are of a _like bigness_, and _figure_, and _matter_, will _hold_, or _dance_ together, and those which are of a _differing_ kind will be _thrust_ or _shov’d_ out from between them; for particles that are _similar_, will, like so many _equal musical strings equally stretcht_, vibrate together in a kind of _Harmony_ or _unison_; whereas others that are _dissimilar_, upon what account soever, unless the disproportion be otherwise counter-ballanc’d, will, like so many _strings out of tune_ to those unisons, though they have the same agitating _pulse_, yet make quite _differing_ kinds of _vibrations_ and _repercussions_, so that though they may be both mov’d, yet are their _vibrations_ so _different_, and so _untun’d_, as ’twere to each other, that they _cross_ and _jar_ against each other, and consequently, _cannot agree_ together, but _fly back_ from each other to their similar particles. Now, to give you an instance how the _disproportion_ of some bodies in one respect, may be _counter-ballanc’d_ by a _contrary disproportion_ of the same body in another respect, whence we find that the subtil _vinous spirit_ is _congruous_, or does readily _mix_ with _water_, which in many properties is of a very _differing nature_, we may consider that a _unison_ may be made either by two _strings_ of the same _bigness_, _length_, and _tension_, or by two strings of the same _bigness_, but of _differing length_, and a _contrary differing tension_, or _3ly._ by two strings of _unequal length_ and _bigness_, and of a _differing tension_, or of _equal length_, and _differing bigness_ and _tension_, and several other such varieties. To which _three properties_ in _strings_, will correspond _three proprieties_ also in _sand_, or the _particles_ of bodies, their _Matter_ or _Substance_, their _Figure_ or _Shape_, and their _Body_ or _Bulk_. And from the _varieties_ of these _three_, may arise _infinite varieties_ in fluid bodies, though all agitated by the _same pulse_ or _vibrative_ motion. And there may be as many ways of making Harmonies and Discords with these, as there may be with _musical strings_. Having therefore seen what is the cause of Congruity or Incongruity, those relative properties of fluids, we may, from what has been said, very easily collect, what is the _reason_ of those Relative proprieties also between _fluid bodies_ and _solid_; for since all bodies consist of _particles_ of such a _Substance_, _Figure_, and _Bulk_; but in some they are _united_ together more _firmly_ then to be _loosened_ from each other by every _vibrative_ motion (though I imagine that there is no body in the world, but that some degree of agitation may, as I hinted before, agitate and loosen the particles so as to make them fluid) those _cohering_ particles may _vibrate_ in the same manner almost as those that are _loose_ and become _unisons_ or _discords_, as I may so speak, to them. Now that the _parts_ of all _bodies_, though never so _solid_, do yet _vibrate_, I think we need go no further for proof, then that _all_ bodies have some _degrees_ of _heat_ in them, and that there has not been yet found any thing _perfectly cold_: Nor can I believe indeed that there is any such thing in Nature, as a body whose particles are at _rest_, or _lazy_ and _unactive_ in the great _Theatre_ of the _World_, it being quite _contrary_ to the grand _Oeconomy_ of the Universe. We see therefore what is the reason of the _sympathy_ or uniting of some bodies together, and of the _antipathy_ or flight of others from each other: For _Congruity_ seems nothing else but a _Sympathy_, and _Incongruity_ an _Antipathy_ of bodies, hence _similar_ bodies once _united_ will not _easily part_, and _dissimilar_ bodies once _disjoyn’d_ will not _easily unite_ again; from hence may be very easily deduc’d the reason of the _suspension_ of _water_ and _Quick-silver_ above their usual _station_, as I shall more at large anon shew.

These properties therefore (alwayes the concomitants of fluid bodies) produce these following visible _Effects_:

First, They _unite_ the parts of a fluid to its _similar_ Solid, or keep them _separate_ from its _dissimilar_. Hence _Quick-silver_ will (as we noted before) _stick_ to _Gold_, _Silver_, _Tin_, _Lead_, &c. and _unite_ with them: but _roul_ off from _Wood_, _Stone_, _Glass_, &c. if never so little scituated out of its _horizontal level_; and _water_ that will _wet salt_ and _dissolve_ it, will _slip_ off from _Tallow_, or the like, without at all _adhering_; as it may likewise be observed to do upon a _dusty_ superficies. And next they cause the parts of _homogeneal fluid_ bodies readily to _adhere_ together and _mix_, and of _heterogeneal_, to be exceeding _averse_ thereunto. Hence we find, that _two_ small _drops_ of _water_, on any superficies they can roul on, will, if they chance to touch each other, _readily unite_ and _mix_ into one 3d _drop_: The like may be observed with two small _Bowls_ of _Quick-silver_ upon a Table or Glass, provided their surfaces be not _dusty_; and with two drops of _Oyl_ upon fair water, _&c._ And further, _water_ put unto _wine_, _salt water_, _vinegar_, _spirit_ of _wine_, or the like, does immediately (especially if they be shaken together) _disperse_ it self all over them. Hence, on the contrary, we also find, that _Oyl of Tartar_ poured upon _Quick-silver_, and _Spirit of Wine_ on that _Oyl_, and _Oyl of Turpentine_ on that _Spirit_, and _Air_ upon that _Oyl_, though they be stopt closely up into a Bottle, and _shaken_ never so much, they will by no means long suffer any of their bigger parts to be _united_ or included within any of the other Liquors (by which recited Liquors, may be plainly enough represented the four _Peripatetical Elements_, and the more subtil _Æther_ above all.) From this property ’tis, that a drop of _water_ does not mingle with, or vanish into _Air_, but is _driven_ (by that Fluid equally protruding it on every side) and forc’t into as little a space as it can possibly be contained in, namely, into a _Round Globule_. So likewise a little _Air_ blown under the _water_, is _united_ or thrust into a _Bubble_ by the ambient water. And a parcel of _Quick-silver_ enclosed with _Air_, _Water_, or almost any other _Liquor_, is _formed_ into a _round Ball_.

Now the cause why all these included Fluids, newly mentioned, or as many others as are wholly included within a heterogeneous fluid, are not _exactly_ of a _Spherical Figure_ (seeing that if caused by these Principles only, it could be of no other) must proceed from some other kind of _pressure_ against the two opposite flatted sides. This _adventitious_ or _accidental pressure_ may proceed from _divers causes_, and accordingly must _diversifie_ the Figure of the included heterogeneous fluid: For seeing that a body may be included either with a fluid only, or only with a solid, or partly with a fluid, and partly with a solid, or partly with one fluid, and partly with another; there will be found a very great variety of the terminating _surfaces_, much differing from a _Spherical_, according to the various resistance or pressure that belongs to each of these encompassing bodies.

Which Properties may in general be deduced from two heads, _viz._ _Motion_, and _Rest_. For, either this Globular Figure is altered by a _natural Motion_, such as is _Gravity_, or a _violent_, such as is any _accidental motion_ of the fluids, as we see in the _wind_ ruffling up the water, and the _purlings_ of _Streams_, and _foaming_ of _Catarracts_, and the like. Or thirdly, By the _Rest_, _Firmness_ and _Stability_ of the ambient _Solid_. For if the including _Solid_ be of an _angular_ or any other _irregular_ Form, the included _fluid_ will be near of the _like_, as a Pint-_Pot_ full of _water_, or a _Bladder_ full of _Air_. And next, if the including or included fluid have a greater _gravity_ one than another, then will the _globular_ Form be deprest into an _Elliptico-spherical_: As if, for example, we suppose the Circle _ABCD_, in the _fourth Figure_, to represent a _drop of water_, _Quick-silver_, or the like, included with the _Air_ or the like, which supposing there were no _gravity_ at all in either of the _fluids_, or that the _contained_ and _containing_ were of the _same weight_, would be _equally comprest_ into an exactly _spherical_ body (the ambient fluid _forcing equally_ against every side of it.) But supposing either a greater _gravity_ in the included, by reason whereof the parts of it being _prest_ from _A_ towards _B_, and thereby the whole put into _motion_, and that _motion_ being _hindred_ by the _resistance_ of the _subjacent_ parts of the ambient, the _globular_ Figure _ADBC_ will be _deprest_ into the _Elliptico-spherical_, _EGFH_. For the side _A_ is _detruded_ to _E_ by the _Gravity_, and _B_ to _F_ by the _resistance_ of the subjacent medium: and therefore _C_ must necessarily be thrust to _G_; and _D_ to _H_. Or else, supposing a greater _gravity_ in the _ambient_, by whose more then ordinary _pressure_ against the under side of the included globule; _B_ will be forced to _F_, and by its _resistance_ of the motion _upwards_, the side _A_ will be _deprest_ to _E_, and therefore _C_ being thrust to _G_ and _D_ to _H_; the _globular_ Figure by this means also will be made an _Elliptico-spherical_. Next if a fluid be included _partly_ with one, and _partly_ with another fluid, it will be found to be shaped _diversly_, according to the proportion of the _gravity_ and _incongruity_ of the 3 _fluids_ one to another: As in the _second Figure_, let the upper _MMM_ be _Air_, the middle _LMNO_ be common _Oyl_, the lower _OOO_ be _Water_, the _Oyl_ will be form’d, not into a _spherical_ Figure, such as is represented by the _pricked Line_, but into such a Figure as LMNO, whose side LMN will be of a flatter _Elliptical_ Figure, by reason of the great disproportion between the _Gravity_ of _Oyl_ and _Air_, and the side LOM of a rounder, because of the smaller difference between the weight of _Oyl_ and _Water_. Lastly, The _globular_ Figure will be changed, if the _ambient_ be partly _fluid_ and partly _solid_. And here the termination of the incompassed _fluid_ towards the incompassing is shap’d according to the proportion of the congruity or incongruity of the _fluids_ to the _solids_, and of the gravity and incongruity of the _fluids_ one to another. As suppose the subjacent _medium_ that hinders an included fluids descent, be a _solid_, as let KI, in the _fourth Figure_, represent the smooth superficies of a _Table_; EGFH, a parcel of _running Mercury_; the side GFH will be more flatted, according to the proportion of the incongruity of the _Mercury_ and _Air_ to the _Wood_, and of the _gravity_ of _Mercury_ and _Air_ one to another; The side GEH will likewise be a little more deprest by reason the subjacent parts are now at rest, which were before in motion.