OF 



CHAPTER XII. 



ON CRYSTALLINE AND SLATY CLEAVAGE.* 



WHEN the student of physical science has to investigate 

 the character of any natural force, Ms first care must be to 

 purify it from the mixture of other forces, and thus study 

 its simple action. If, for example, he wishes to know how 

 a mass of liquid would shape itself if at liberty to follow 

 the bent of its own molecular forces, he must see that 

 these forces have free and undisturbed exercise. We 

 might perhaps refer him to the dewdrop for a solution of 

 the question; but here we have to do, not only with the 

 action of the molecules of the liquid upon each other, but 

 also with the action of gravity upon the mass, which pulls 

 the drop downward and elongates it. If he would examine 

 the problem in its purity, he must do as Plateau has done, 

 detach the liquid mass from the action of gravity; he 

 would then find the shape to be a perfect sphere. Natural 

 processes come to us in a mixed manner, and to the un- 

 instructed mind are a mass of unintelligible confusion. 

 Suppose half a dozen of the best musical performers to be 

 placed in the same room, each playing his own instrument 

 to perfection, but no two playing 'the same tune; though 

 each individual instrument might be a source of perfect 

 music, still the mixture of all would produce mere noise. 

 Thus it is with the processes of nature, where mechanical 

 and molecular laws intermingle and create apparent con- 

 fusion. Their mixture constitutes what may be called the 

 noise of natural laws, and it is the vocation of the man of 

 science to resolve this noise into its components, and thus 

 to detect the underlying music. 



The necessity of this detachment of one force from all 

 other forces is nowhere more strikingly exhibited than in 

 the phenomena of crystallization. Here, for example, is a 

 solution of common sulphate of soda or Glauber salt. 

 Looking into ii mentally, we see the molecules of that 

 liquid, like disciplined squadrons under a governing eye, 

 arranging themselves into battalions, gathering round dis- 

 tinct centers, and forming themselves into solid masses, 



* From a discourse delivered in the Royal Institution of Great 

 Britain, June 6, 1856. 



