_B._ It is probable it would. But it may be they know no salt that howsoever prepared, which, with how great a fire soever, can make them melt. And, it may be, the true crystal of the mountain, which is found in great pieces in the Alps, is but a compound of many small ones, and made by the earth’s annual motion; for it is a very swift motion. Suppose now that within a very small cavern of those rocks whose smallest atoms are crystal, and the cavity filled with air; and consider what a tumult would be made by the swift reciprocation of that air; whether it would not in time separate those atoms from the rock, and jumbling them together make them rub off their scurf from one another, and by little and little to touch one another in polished planes, and consequently stick together, till in length of time they become one lump of clean crystal. _A._ I believe that the least parts of created substances lay mingled together at first, till it pleased God to separate all dissimilar natures, and congregate the similar, to which this annual motion is proper. But they say that crystal is found in the open air hanging like icicles upon the rocks, which, if true, defeats this supposition of a narrow cavern, and therefore I must have some farther experience of it before I make it my opinion. But howsoever, it still holds true that diaphanous bodies of all sorts, in their least parts, were made by God in the beginning of the world. But it may be true, notwithstanding those icicles. For the force of the air that could break off those diaphanous atoms in a cavern, can do the same in the open air. And I know that a less force of air can break some bodies into small pieces, not much less hard than crystal, by corrupting them. _B._ That which you now have said is somewhat. But I deny not the possibility, but only doubt of the operation. You may therefore pass to some other question. _A._ Well, I will ask you then a question about refraction. I know already that for the cause of refraction, when the light falleth through a thinner medium upon a thicker, you assign the resistance of the thicker body; but you do not mean there, by _rarum_ and _densum_, two bodies whereof in equal spaces one has more substance in it than the other. _B._ No; for equal spaces contain equal bodies. But I mean by _densum_ any body which more resisteth the motion of the air, and by _rarum_ that which resisteth less. _A._ But you have not declared in what that resistance consisteth. _B._ I suppose it proceedeth from the hardness. _A._ But from thence it will follow, that all transparent bodies that equally refract are equally hard, which I think is not true, because the refraction of glass is not greater, at least in comparison of their hardnesses, than that of water.