48 



COHESION. 



up. I may even bend it 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 in- 

 jury. 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 



Fig. 15. 



Fig. 16. 



Fiq. 17. 



crystals; for there is some salt (fig. 16) you 

 know what common salt is ( 13 ) ; here is a piece 

 of this salt which by natural circumstances has 

 had its particles so brought together that they 

 have been allowed free opportunity of combin- 

 ing or coalescing, and you shall see what 

 happens if I take this piece of salt and break 

 it. It does not break as flint did, or as the 

 mica did, but with a clean sharp angle and 



