PG15491.B00501
Upon this Occasion, I hope it will not be altogether unseasonable, if I propound my conjectures and _Hypothesis_ about the _medium_ and conveyance of light.

PG15491.B00502
I suppose then, that the greatest part of the _Interstitia_ of the world, that lies between the bodies of the Sun and Starrs, and the Planets, and the Earth, to be an exceeding fluid body, very apt and ready to be mov’d, and to communicate the motion of any one part to any other part, though never so far distant: Nor do I much concern my self, to determine what the Figure of the particles of this exceedingly subtile fluid _medium_ must be, nor whether it have any interstitiated pores or vacuities, it being sufficient to solve all the _Phænomena_ to suppose it an exceedingly fluid, or the most fluid body in the world, and as yet impossible to determine the other difficulties.

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That being so exceeding fluid a body, it easily gives passage to all other bodies to move to and fro in it.

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That it neither receives from any of its parts, or from other bodies; nor communicates to any of its parts, or to any other body, any impulse, or motion in a direct line, that is not of a determinate quickness. And that when the motion is of such determinate swiftness, it both receives, and communicates, or propagates an impulse or motion to any imaginable distance in streight lines, with an unimaginable celerity and vigour.

PG15491.B00505
That all kind of solid bodies consist of pretty massie particles in respect of the particles of this fluid _medium_, which in many places do so touch each other, that none of this fluid _medium_ interposes much after the same manner (to use a gross similitude) as a heap of great stones compose one great _congeries_ or mass in the midst of the water.

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That all fluid bodies which we may call _tangible_, are nothing but some more subtile parts of those particles, that serve to constitute all _tangible_ bodies.

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That the water, and such other fluid bodies, are nothing but a _congeries_ of particles agitated or made fluid by it in the same manner as the particles of _Salt_ are agitated or made fluid by a parcel of water, in which they are dissolv’d, and subsiding to the bottom of it, constitute a fluid body, much more massie and dense, and less fluid then the pure water it self.

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That the air on the other side is a certain company of particles of quite another kind, that is, such as are very much smaller, and more easily moveable by the motion of this fluid _medium_; much like those very subtile parts of _Cochenel_, other very deep tinging bodies, where by a very small parcel of matter is able to tinge and diffuse it self over a very great quantity of the fluid dissolvent; or somewhat after that manner, as smoak, and such like minute bodies, or steams, are observ’d to tinge a very great quantity of air; onely this last similitude is deficient in one propriety, and that is a perpetuity or continuance in that state of commixture with the air, but the former does more nearly approach to the nature and manner of the air’s being dissolv’d by this fluid or _Æther_. And this Similitude will further hold in these proprieties; that as those tinctures may be increased by certain bodies, so may they be precipitated by others, as I shall afterwards shew it to be very probable, that the like accidents happen even to the Air it self.

PG15491.B00509
Further, as these solutions and tinctures do alter the nature of these fluid bodies, as to their aptness to propagate a motion or impulse through them, even so does the particles of the Air, Water, and other fluid bodies, and of Glass, Crystal, &c. which are commixt with this bulk of the _Æther_ alter the motion of the propagated pulse of light; that is, where these more bulkie particles are more plentifull, and consequently a lesser quantity of the _Æther_ between them to be mov’d, there the motion must necessarily be the swifter, though not so robust, which will produce those effects, which I have (I hope) with some probability, ascribed to it in the digression about Colours, at the end of the _Observations_ on _Muscovy-glass._

PG15491.B00510
Now, that other Stones, and those which have the closest and hardest textures, and seem (as far as we are able to discover with our eyes, though help’d with the best _Microscopes_) freest from pores, are yet notwithstanding replenish’d with them, an Instance or two will, I suppose, make more probable.

PG15491.B00511
A very solid and unflaw’d piece of cleer white _Marble_, if it be well polish’d and glaz’d, has so curiously smooth a surface, that the best and most polish’d surface of any wrought-glass, seems not to the naked eye, nor through a _Microscope_, to be more smooth, and less porous. And yet, that this hard close body is replenish’d with abundance of pores, I think these following Experiments will sufficiently prove.

PG15491.B00512
The first is, That if you take such a piece, and for a pretty while boyl it in Turpentine and Oyl of Turpentine, you shall find that the stone will be all imbu’d with it; and whereas before it look’d more white, but more opacous, now it will look more greasie, but be much more transparent, and if you let it lie but a little while, and then break off a part of it, you shall find the unctuous body to have penetrated it to such a determinate depth every way within the surface. This may be yet easier try’d with a piece of the same _Marble_, a little warm’d in the fire, and then a little Pitch or Tarr melted on the top of it; for these black bodies, by their insinuating themselves into the invisible pores of the stone, ting it with so black a hue, that there can be no further doubt of the truth of this assertion, that it abounds with small imperceptible pores.

PG15491.B00513
Now, that other bodies will also sink into the pores of _Marble_, besides unctuous, I have try’d, and found, that a very Blue tincture made in _spirit of Urine_ would very readily and easily sink into it, as would also several tinctures drawn with _spirit of Wine_.

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Nor is _Marble_ the only seemingly close stone, which by other kinds of Experiments may be found porous; for I have by this kind of Experiment on divers other stones found much the same effect, and in some, indeed much more notable. Other stones I have found so porous, that with the _Microscope_ I could perceive several small winding holes, much like Worm-holes, as I have noted in some kind of _Purbeck-stone_, by looking on the surface of a piece newly flaw’d off, for if otherwise, the surface has been long expos’d to the Air, or has been scraped with any tool, those small caverns are fill’d with dust, and disappear.

PG15491.B00515
And to confirm this _Conjecture_, yet further, I shall here insert an excellent account, given into the _Royal Society_ by that Eminently Learned Physician, Doctor _Goddard_, of an Experiment, not less instructive then curious and accurate, made by himself on a very hard and seemingly close stone call’d _Oculus Mundi_, as I find it preserv’d in the Records of that Honourable Society.

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A small stone of the kind, call’d by some Authours, _Oculus Mundi_, being dry and cloudy, weigh’d 5²⁰⁹⁄₂₅₆ _Grains_.

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The same put under water for a night, and somewhat more, became transparent, and the superficies being wiped dry, weighed 6³⁄₂₅₆ _Grains_.

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The difference between these two weights, 0⁵⁰⁄₂₅₆ of a _Grain_.

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The same Stone kept out of water one Day and becoming cloudy again weighed, 5²²⁵⁄₂₅₆ _Graines_.

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Which was more then the first weight, 0¹⁶⁄₂₅₆ of a _Grain_.

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The same being kept two Days longer weighed, 5²⁰²⁄₂₅₆ _Graines_.

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Which was less then at first, 0⁷⁄₂₅₆ a _Grain_.

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Being kept dry something longer it did not grow sensibly lighter.

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Being put under water for a night and becoming again transparent and wiped dry, the weight was, _6³⁄₂₅₆ Grains_, the same with the first after putting in water, and more then the last weight after keeping of it dry, 0⁵⁷⁄₂₅₆ of a _Grain_.

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Another Stone of the same kind being variegated with milky _white_ and _gray_ like some sorts of _Agates_, while it lay under water, was alwaies invironed with little Bubbles, such as appear in water a little before boyling, next the sides of the Vessel.

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There were also some the like Bubbles on the Surface of the water just over it, as if either some exhalations came out of it, or that it did excite some fermentation in the parts of the water contiguous to it.

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There was little sensible difference in the transparency of this Stone, before the putting under water, and after: To be sure the milky-_white_ parts continued as before, but more difference in weight then in the former. For whereas before the putting into the water the weight was 18⁹⁷⁄₁₂₈ _Graines_. After it had lyen in about four and twenty hours the weight was 20²⁷⁄₁₂₈ _Graines_, so the difference was, 1⁵⁸⁄₁₂₈ _Graines_.

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The same Stone was infused in the water scalding hot, and so continued for a while after it was cold, but got no more weight then upon infusing in the cold, neither was there any sensible Difference in the weight both times.

PG15491.B00529
In which Experiment, there are three Observables that seem very manifestly to prove the porousness of these seemingly close bodies: the first is their acquiring a transparency, and losing their whiteness after steeping in water, which will seem the more strongly to argue it, if what I have already said about the making transparent, or clarifying of some bodies, as the white powder of beaten Glass, and the froth of some glutinous transparent liquor be well consider’d; for thereby it will seem rational to think that this transparency arises from the insinuation of the water (which has much the same refraction with such stony particles, as may be discover’d by Sand view’d with a _Microscope_) into those pores which were formerly repleat with air (that has a very differing refraction, and consequently is very reflective) which seems to be confirm’d by the second Observable, namely, the increase of weight after keeping, and decrease upon drying. And thirdly, seem’d yet more sensibly confirm’d by the multitude of bubbles in the last Experiment.

PG15491.B00530
We find also most Acid Salts very readily to dissolve and separate the parts of this body one from another; which is yet a further Argument to confirm the porousness of bodies, and will serve as such, to shew that even Glass also has an abundance of pores in it, since there are several liquors, that with long staying in a Glass, will so _Corrode_ and eat into it, as at last, to make it pervious to the liquor it contain’d, of which I have seen very many Instances.

PG15491.B00531
Since therefore we find by other proofs, that many of those bodies which we think the most solid ones, and appear so to our sight, have notwithstanding abundance of those grosser kind of pores, which will admit several kinds of liquors into them, why should we not believe that Glass, and all other transparent bodies abound with them, since we have many other arguments, besides the propagation of light, which seem to argue for it?

PG15491.B00532
And whereas it may be objected, that the propagation of light is no argument that there are those atomical pores in glass, since there are _Hypotheses_ plausible enough to solve those _Phænomena_, by supposing the pulse onely to be communicated through the transparent body.

PG15491.B00533
To this I answer, that that _Hypothesis_ which the industrious _Mersennus_ has publish’d about the slower motion of the end of a Ray in a denser _medium_, then in a more rare and thin, seems altogether unsufficient to solve abundance of _Phænomena_, of which this is not the least considerable, that it is impossible from that supposition, that any colours should be generated from the refraction of the Rays; for since by that _Hypothesis_ the _undulating pulse_ is always carried perpendicular, or at right angles with the Ray or Line of direction, it follows, that the stroke of the pulse of light, after it has been once or twice refracted (through a Prisme, for example) must affect the eye with the same kind of stroke as if it had not been refracted at all. Nor will it be enough for a Defendant of that _Hypothesis_, to say, that perhaps it is because the refractions have made the Rays more weak, for if so, then two refractions in the two parallel sides of a _Quadrangular Prisme_ would produce colours, but we have no such _Phænomena_ produc’d.

PG15491.B00534
There are several Arguments that I could bring to evince that there are in all transparent bodies such atomical pores. And that there is such a fluid body as I am arguing for, which is the _medium_, or Instrument, by which the pulse of Light is convey’d from the _lucid body_ to the enlightn’d. But that it being a digression from the Observations I was recording, about the Pores of _Kettering-Stone_, it would be too much such, if I should protract it too long; and therefore I shall proceed to the next _Observation_.

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* * * * *

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Observ. XVI. _Of _Charcoal_, or burnt _Vegetables_._

PG15491.B00537
Charcoal, or a Vegetable burnt black, affords an object no less pleasant than instructive, for if you take a small round Charcoal, and break it short with your fingers, you may perceive it to break with a very smooth and sleek surface, almost like the surface of black sealing Wax; this surface, if it be look’d on with an ordinary _Microscope_, does manifest abundance of those pores which are also visible to the eye in many kinds of _Wood_, rang’d round the pith, both a in kind of circular order, and a radiant one. Of these there are a multitude in the substance of the Coal, every where almost perforating and drilling it from end to end; by means of which, be the Coal never so long, you may easily blow through it; and this you may presently find, by wetting one end of it with Spittle, and blowing at the other.

PG15491.B00538
But this is not all, for besides those many great and conspicuous irregular spots or pores, if a better _Microscope_ be made use of, there will appear an infinite company of exceedingly small, and very regular pores, so thick and so orderly set, and so close to one another, that they leave very little room or space between them to be fill’d with a solid body, for the apparent _interstitia_ or separating sides of these pores seem so thin in some places, that the texture of a Honey-comb cannot be more porous. Though this be not every where so, the intercurrent partitions in some places being very much thicker in proportion to the holes.

PG15491.B00539
Most of these small pores seem’d to be pretty round, and were rang’d in rows that radiated from the pith to the bark; they all of them seem’d to be continued open pores, running the whole length of the Stick; and that they were all perforated, I try’d by breaking off a very thin sliver of the Coal cross-ways, and then with my _Microscope_, diligently surveying them against the light, for by that means I was able to see quite through them.

PG15491.B00540
These pores were so exceeding small and thick, that in a line of them, ¹⁄₁₈ part of an Inch long, I found by numbering them no less then 150. small pores; and therefore in a line of them an Inch long, must be no less then 2700. pores, and in a circular _area_ of an Inch diameter, must be about 5725350. of the like pores; so that a Stick of an Inch Diameter, may contain no less then seven hundred and twenty five thousand, besides 5 Millions of pores, which would, I doubt not, seem even incredible, were not every one left to believe his own eyes. Nay, having since examin’d _Cocus, black and green Ebony, Lignum Vitæ_, &c. I found, that all these Woods have their pores, abundantly smaller then those of soft light Wood; in so much, that those of _Guajacum_ seem’d not above an eighth part of the bigness of the pores of Beech, but then the _Interstitia_ were thicker; so prodigiously curious are the contrivances, pipes, or sluces by which the _Succus nutritius_, or Juyce of a Vegetable is convey’d from place to place.

PG15491.B00541
This _Observation_ seems to afford us the true reason of several _Phænomena_ of Coals; as

PG15491.B00542
First, why they look black; and for this we need go no further then the _Scheme_, for certainly, a body that has so many pores in it as this is discover’d to have, from each of which no light is reflected, must necessarily look black, especially, when the pores are somewhat bigger in proportion to the intervals then they are cut in the _Scheme_, black being nothing else but a privation of Light, or a want of reflection; and wheresoever this reflecting quality is deficient, there does that part look black, whether it be from a porousness of the body, as in this Instance, or in a deadning and dulling quality, such as I have observ’d in the _Scoria_ of Lead, Tin, Silver, Copper, &c.

PG15491.B00543
Next, we may also as plainly see the reason of its shining quality, and that is from the even breaking off of the stick, the solid _interstitia_ having a regular termination or surface, and having a pretty strong reflecting quality, the many small reflections become united to the naked eye, and make a very pretty shining surface.

PG15491.B00544
Thirdly, the reason of its hardness and brittleness seems evident, for since all the watery or liquid substance that moistn’d and toughn’d those _Interstitia_ of the more solid parts, are evaporated and remov’d, that which is left behind becomes of the nature almost of a stone, which will not at all, or very little, bend without a _divulsion_ or _solution_ of its _continuity_.

PG15491.B00545
It is not my design at present, to examine the use and _Mechanisme_ of these parts of Wood, that being more proper to another Enquiry; but rather to hint, that from this Experiment we may learn,

PG15491.B00546
First, what is the cause of the blackness of many burnt bodies, which we may find to be nothing else but this; that the heat of the fire agitating and rarifying the waterish, transparent, and volatile water that is contain’d in them, by the continuation of that action, does so totally expel and drive away all that which before fill’d the pores, and was dispers’d also through the solid mass of it, and thereby caus’d an universal kind of transparency, that it not onely leaves all the pores empty, but all the _Interstitia_ also so dry and _opacous_, and perhaps also yet further perforated, that that light onely is reflected back which falls upon the very outward edges of the pores, all they that enter into the pores of the body, never returning, but being lost in it.

PG15491.B00547
Now, that the Charring or coaling of a body is nothing else, may be easily believ’d by one that shall consider the means of its production, which may be done after this, or any such manner. The body to be charr’d or coal’d, may be put into a _Crucible_, Pot, or any other Vessel that will endure to be made red-hot in the fire without breaking, and then cover’d over with Sand, so as no part of it be suffer’d to be open to the Air, then set into a good fire, and there kept till the Sand has continu’d red hot for a quarter, half, an hour or two, or more, according to the nature and bigness of the body to be coal’d or charr’d, then taking it out of the fire, and letting it stand till it be quite cold, the body may be taken out of the Sand well charr’d and cleans’d of its waterish parts; but in the taking of it out, care must be had that the Sand be very neer cold, for else, when it comes into the free air, it will take fire, and readily burn away.

PG15491.B00548
This maybe done also in any close Vessel of Glass, as a _Retort_, or the like, and the several fluid substances that come over may be receiv’d in a fit _Recipient_, which will yet further countenance this _Hypothesis_: And their manner of charring Wood in great quantity comes much to the same thing, namely, an application of a great heat to the body, and preserving it from the free access of the devouring air; this may be easily learn’d from the History of Charring of Coal, most excellently describ’d and publish’d by that most accomplish’d Gentleman, Mr. _John Evelin_, in the 100, 101, 103, pages of his _Sylva_, to which I shall therefore refer the curious Reader that desires a full information of it.

PG15491.B00549
Next, we may learn what part of the Wood it is that is the _combustible_ matter, for since we shall find that none, or very little of those fluid substances that are driven over into the Receiver are _combustible_, and that most of that which is left behind is so, it follows, that the solid _interstitia_ of the Wood are the _combustible_ matter. Further, the reason why uncharr’d Wood burns with a greater flame then that which is charr’d, is as evident, because those waterish or volatil parts issuing out of the fired Wood, every way, not onely shatter and open the body, the better for the fire to enter, but issuing out in vapours or wind, they become like so many little _æolipiles_, or Bellows, whereby they blow and agitate the fir’d part, and conduce to the more speedy and violent consumption or dissolution of the body.

PG15491.B00550
Thirdly, from the Experiment of charring of Coals (whereby we see that notwithstanding the great heat, and the duration of it, the solid parts of the Wood remain, whilest they are preserv’d from the free access of the air undissipated) we may learn, that which has not, that I know of, been publish’d or hinted, nay, not so much as thought of, by any; and that in short is this.

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First, _that the Air_ in which we live, move, and breath, and which encompasses very many, and cherishes most bodies it encompasses, that this Air is the _menstruum_, or universal dissolvent of all _Sulphureous_ bodies.

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Secondly, _that this action_ it performs not, till the body be first sufficiently heated, as we find requisite also to the dissolution of many other bodies by several other _menstruums_.

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Thirdly, _that this action_ of dissolution, produces or generates a very great heat, and that which we call Fire; and this is common also to many dissolutions of other bodies, made by _menstruums_, of which I could give multitudes of Instances.

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Fourthly, _that this action_ is perform’d with so great a violence, and does so minutely act, and rapidly agitate the smallest parts of the _combustible_ matter, that it produces in the _diaphanous medium_ of the Air, the action or pulse of light, which what it is, I have else-where already shewn.

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Fifthly, _that the dissolution_ of sulphureous bodies is made by a substance inherent, and mixt with the Air, that is like, if not the very same, with that which is fixt in _Salt-peter_, which by multitudes of Experiments that may be made with _Salt-peter_, will, I think, most evidently be demonstrated.

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Sixthly, _that in this dissolution_ of bodies by the Air, a certain part is united and mixt, or dissolv’d and turn’d into the Air, and made to fly up and down with it in the same manner as a _metalline_ or other body dissolved into any _menstruums_, does follow the motions and progresses of that _menstruum_ till it be precipitated.

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Seventhly, That as there is one part that is dissoluble by the Air, so are there other parts with which the parts of the Air mixing and uniting, do make a _Coagulum_, or _precipitation_, as one may call it, which causes it to be separated from the Air, but this _precipitate_ is so light, and in so small and rarify’d or porous clusters, that it is very volatil, and is easily carry’d up by the motion of the Air, though afterwards, when the heat and agitation that kept it rarify’d ceases, it easily condenses, and commixt with other indissoluble parts, it sticks and adheres to the next bodies it meets withall; and this is a certain _Salt_ that may be extracted out of _Soot_.

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Eighthly, that many indissoluble parts being very apt and prompt to be rarify’d, and so, whilest they continue in that heat and agitation, are lighter then the Ambient Air, are thereby thrust and carry’d upwards with great violence, and by that means carry along with them, not onely that _Saline concrete_ I mention’d before, but many terrestrial, or indissoluble and irrarefiable parts, nay, many parts also which are dissoluble, but are not suffer’d to stay long enough in a sufficient heat to make them prompt and apt for that action. And therefore we find in _Soot_, not onely a part, that being continued longer in a competent heat, will be dissolv’d by the Air, or take fire and burn; but a part also which is fixt, terrestrial, and irrarefiable.

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Ninthly, that as there are these several parts that will rarifie and fly, or be driven up by the heat, so are there many others, that as they are indissoluble by the _aerial menstruum_, so are they of such sluggish and gross parts, that they are not easily rarify’d by heat, and therefore cannot be rais’d by it; the volatility or fixtness of a body seeming to consist only in this, that the one is of a texture, or has component parts that will be easily rarify’d into the form of Air, and the other, that it has such as will not, without much ado, be brought to such a constitution; and this is that part which remains behind in a white body call’d Ashes, which contains a substance, or _Salt_, which Chymists call _Alkali_: what the particular natures of each of these bodies are, I shall not here examine, intending it in another place, but shall rather add that this _Hypothesis_ does so exactly agree with all _Phænomena_, of Fire, and so genuinely explicate each particular circumstance that I have hitherto observ’d, that it is more then probable, that this cause which I have assign’d is the true adequate, real, and onely cause of those _Phænomena_; And therefore I shall proceed a little further, to shew the nature and use of the Air.
