1868. | Mathematical and Physical Science. 509 
Egypt without inquiring whence they came. How, then, are those 
salt-pyramids built up ? 
Guided by analogy, we may suppose that, swarming among the 
constituent molecules of the salt, there is an invisible population, 
euided and coerced by some invisible master, and placing the atomic 
blocks in their positions. This, however, is not the scientific idea. 
The scientific idea is, that the molecules act upon each other without 
the intervention of slave labour; that they attract each other and 
repel each other at certain definite points, 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 forces 
with which they act upon each other. Throughout inorganic 
nature, we have this formative power,—this structural energy 
ready to come into play, and build the ultimate particles of matter 
into definite shapes. It is present everywhere. The ice of our 
winters and of our polar regions is its handywork, and so equally 
are the quartz, felspar, and mica of our rocks. 
Let us pass from what we are accustomed to regard as a dead 
mineral to a living grain of corn. In the corn the molecules are 
also set in definite positions. But what has built together the mole- 
cules of the corn? Regarding crystalline architecture, we may, if we 
please, consider the atoms and molecules to be placed in position by 
a power external to themselves. The same hypothesis is open to us 
now. But if in the case of crystals we have rejected this notion 
of an external architect, we are bound to reject it now, and to con- 
clude that the molecules of the corn are self-posited by the forces 
with which they act upon each other. It would be poor philosophy 
to invoke an external agent in the one case and to reject it in the 
other. 
Let us now place the grain of corn in the earth and subject it 
to a certain degree of warmth. In other words, let the molecules, 
both of the corn and of the surrounding earth, be kept in a state 
of agitation; for warmth is, in the eye of science, tremulous mole- 
cular motion. Under these circumstances, the grain and the sub- 
stances which surround it interact, and a molecular architecture is 
the result of this interaction. A bud is formed; this bud reaches 
the surface, where it is exposed to the sun’s rays, which are also 
to be regarded as a kind of vibratory motion. And as the common 
motion of heat with which the grain and the substances surround- 
ing it were first endowed, enabled the grain and these substances 
to coalesce, so the specific motion of the sun’s rays now enables the 
green bud to feed upon the carbonic acid and the aqueous vapour of 
the air, appropriating those constituents of both for which the blade 
has an elective attraction, and permitting the other constituent to 
