402 FRAGMENTS OF SCIENCE. 
oration continues, solidification goes on, and we finally 
obtain through the clustering together of innumerable 
molecules, a finite crystalline mass of a definite form. 
What is this form? It sometimes seems a mimicry of the 
architecture of Egypt. We have little pyramids built by 
the salt, terrace above terrace from base to apex, forming a 
series^of steps resembling those up which the traveler in 
Egypt is dragged by his guides. The human mind is as 
little disposed to look without questioning at these pyra- 
midal salt-crystals, as to look at the pyramids of Egypt, 
without inquiring whence they came. How, then, are 
those salt-pyramids built up? 
Guided by analogy, you may, if you like, suppose that, 
swarming among the constituent molecules of the salt, 
there is an invisible population, controlled and coerced by 
some invisible master, placing the atomic blocks in their 
positions. This, however, is not the scientific idea, nor do 
I think your good sense will accept it as a likely one. The 
scientific idea is, that the molecules act upon each other 
without the intervention of slave labor; that they attract 
each other, and repel each other, at certain definite points, 
or poles, and in certain definite directions; and that the 
pyramidal form is the result of this play of attraction and 
repulsion. While, then, the blocks of Egypt were laid 
down by a power external to themselves, these molecular 
blocks of salt are self-posited, being fixed in their places by 
the inherent forces with which they act upon each other. 
I take common salt as an illustration, because it is so 
familiar to us all; but any othercrystalline substance would 
answer my purpose equally well. Everywhere, in fact, 
throughout inorganic nature, we have this formative power, 
as Fichte would call it this structural energy ready to 
come into play, and build the ultimate particles of matter 
into definite shapes. The ice of our winters, and of our 
polar regions, is its handiwork, and so also are the quartz, 
feldspar, and mica of our rocks. Our chalk-beds are for the 
most part composed of minute shells, which are also the 
product of structural energy; but behind the shell, as a 
whole, lies a more remote and subtle formative act. These 
shells are built up of little crystals of calc-spar, and, to 
form these crystals, the structural force had to deal with 
the intangible molecules of carbonate of lime. This ten- 
dency on the part of matter to organize itself, to grow into 
