power of cohesion, but that they are held together in very curious ways. And suppose I take some things that are held together by this force, and examine them more minutely. I will first take a bit of glass, and if I give it a blow with a hammer, I shall just break it to pieces. You saw how it was in the case of the flint when I broke the piece off; a piece of a similar kind would come off, just as you would expect; and if I were to break it up still more, it would be as you have seen, simply a collection of small particles of no definite shape or form. But supposing I take some other thing, this stone for instance (fig. 15) [taking a piece of mica[1]], and if I hammer this stone, I may batter it as great deal before I can break it up. I may aven bent id without breaking it; that is to say, I may bend it in one particular direction without breaking it much, although I feel in my hands that I am doing it some injury. But now, if I take it by the edges, I find that it breaks up into leaf after leaf in a most extraordinary manner. Why should it break up like that? Not because all stones do, or all crystals; for there is some salt (fig. 16)—you
- ↑ Mica..—A silicate of alumina and magnesia. It has a bright metallic lustre—hence its name, from mico, to shine.
