ent
on their combination has been expended, no further power can be got
out of their mutual attraction. As dynamic agents they are dead. The
materials of the earth's crust consist for the most part of substances
whose atoms have already closed in chemical union--whose mutual
attractions are satisfied. Granite, for instance, is a widely
diffused substance; but granite consists, in great part, of silicon,
oxygen, potassium, calcium, and aluminum, whose atoms united long ago,
and are therefore dead. Limestone is composed of carbon, oxygen, and
a metal called calcium, the atoms of which have already closed in
chemical union, and are therefore finally at rest. In this way we
might go over nearly the whole of the materials of the earth's crust,
and satisfy ourselves that though they were sources of power in ages
past, and long before any creature appeared on the earth capable of
turning their power to account, they are sources of power no longer.
And here we might halt for a moment to remark on that tendency, so
prevalent in the world, to regard everything as made for human use.
Those who entertain this notion, hold, I think, an overweening opinion
of their own importance in the system of nature. Flowers bloomed
before men saw them, and the quantity of power wasted before man could
utilise it is all but infinite compared with what now remains. We are
truly heirs of all the ages; but as honest men it behoves us to learn
the extent of our inheritance, and as brave ones not to whimper if it
should prove less than we had supposed. The healthy attitude of mind
with reference to this subject is that of the poet, who, when asked
whence came the rhodora, joyfully acknowledged his brotherhood with
the flower:

Why thou wert there, O rival of the rose!
I never thought to ask, I never knew,
But in my simple ignorance supposed
The self-same power that brought me there brought you.

Emerson.

A few exceptions to the general state of union of the molecules of the
earth's crust--vast in relation to us, but trivial in comparison to
the total store of which they are the residue--still remain. They
constitute our main sources of motive power. By far the most
important of these are our beds of coal. Distance still intervenes
between the atoms of carbon and those of atmospheric oxygen, across
which the atoms may be urged by their mutual attractions; and we can
utilise the motion