232 FRAGMENTS OF SCIENCE. 
CHA.PTEE XII. 
ON CRYSTALLINE AND SLATY CLEAVAGE.* 
WHEN the student of physical science has to investigate 
the character of any natural force, his first care must be to 
purify it from the mixture of other forces, and thus study 
its simple action. If, for exam pie, 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 it 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. 
