cter of steam from the fire, and we
have now reached the source of the _movement_ of steam, and traced it
to the fire. In fact, we have found the source of power, in this most
mechanical of all mechanical machines, to be removed from the department
of knowledge which treats of machines!

But we need not pause here, although we must now enter a little way into
chemical, instead of mechanical science. The fire prepares the water to
act as a carrier of power; it must contain power, therefore; and what
is it which we call fire? In placing on the grate coal or wood, and
providing for the contact of a continuous current of air, we intend to
bring about certain chemical actions as consequent on a disposition
which we know coal and wood to possess. When we apply fire, the chemical
actions commence and the usual effects follow. Now, if we for a moment
dismiss the consideration of the means adopted, it becomes apparent to
every one, that, as the fire will continue to increase with successive
additions of fuel, or as it will continue indefinitely with a regular
supply, there must be something else than mere motor action here. We
cannot call it chemical action, and dismiss the thought, and neglect
further inquiry, unless we would place ourselves with those who regard
the movement of the steamboat as being due to the machinery.

Our farther progress in this analysis will soon open a wide field of
knowledge and inquiry; but it is sufficient for our present purpose, if,
by a careful study of the composition and chemical disposition of the
proximate compounds of the coal and the wood fuel, we arrive at the
conclusion that both are the result of forces which, very slight in
themselves at any moment, yet when acting through long periods of time
become laid up in the form of coal and wood. All that effort which the
tree has exhibited during its growth from the germ of the seed to its
state of maturity, when taken as fuel, is pent up in its substance,
ready, when fire is applied, to escape slowly and continuously. In
the case of the coal, after the growth of the plant from which it was
formed, the material underwent changes which enabled it to conserve more
forces, and to exhibit more energy when fire is applied to its mass; and
hence the distinction between wood and coal.

Our analysis thus far has developed the source of the power moving
the steamboat as existing in the gradual action of forces influencing
vegetation, concentrated and