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.
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.
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.
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.
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.
A small stone of the kind, call’d by some Authours, Oculus Mundi, being dry and cloudy, weigh’d 5²⁰⁹⁄₂₅₆ Grains.
The same put under water for a night, and somewhat more, became transparent, and the superficies being wiped dry, weighed 6³⁄₂₅₆ Grains.
The difference between these two weights, 0⁵⁰⁄₂₅₆ of a Grain.
The same Stone kept out of water one Day and becoming cloudy again weighed, 5²²⁵⁄₂₅₆ Graines.
Which was more then the first weight, 0¹⁶⁄₂₅₆ of a Grain.
The same being kept two Days longer weighed, 5²⁰²⁄₂₅₆ Graines.
Which was less then at first, 0⁷⁄₂₅₆ a Grain.
Being kept dry something longer it did not grow sensibly lighter.
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.
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.
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.
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.
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.
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.
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.
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?
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.