This also gives us a probable reason of the so much admired _Phænomena_, of the _Oculus Mundi_, an _Oval_ stone, which commonly looks like white Alabaster, but being laid a certain time in Water, it grows _pellucid_, and transparent, and being suffer’d to lie again dry, it by degrees loses that transparency, and becomes white as before. For the Stone being of a hollow spongie nature, has in the first and last of these appearances, all those pores fill’d with the obtunding and reflecting air; whereas in the second, all those pores are fill’d with a _medium_ that has much the same refraction with the particles of the Stone, and therefore those two being _contiguous_, make, as ’twere, one _continued medium_, of which more is said in the 15. _Observation_. There are a multitude of other _Phænomena_, that are produc’d from this same Principle, which as it has not been taken notice of by any yet that I know, so I think, upon more diligent observation, will it not be found the least considerable. But I have here onely time to hint _Hypotheses_, and not to prosecute them so fully as I could wish; many of them having a vast extent in the production of a multitude of _Phænomena_, which have been by others, either not attempted to be explain’d, or else attributed to some other cause than what I have assign’d, and perhaps than the right; and therefore I shall leave this to the prosecution of such as have more leisure: onely before I leave it, I must not pretermit to hint, that by this Principle, multitudes of the _Phænomena_ of the air, as about _Mists_, _Clouds_, _Meteors_, _Haloes_, &c. are most plainly and (perhaps) truly explicable; multitudes also of the _Phænomena_ in colour’d bodies, as liquors, &c. are deducible from it. And from this I shall proceed to a second considerable _Phænomenon_ which these Diamants exhibit, and that is the regularity of their _Figure_, which is a propriety not less general than the former, It comprising within its extent, all kinds of _Metals_, all kinds of _Minerals_, most _Precious stones_, all kinds of _Salts_, multitudes of _Earths_, and almost all kinds of _fluid bodies_. And this is another propiety, which, though a little superficially taken notice of by some, has not, that I know, been so much as attempted to be explicated by any.