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 locked up in the fuel. For the purpose of illustrating the subject of this essay, we require no farther progress in this direction. A moment of thought at this point and we shall cease to consider steam-power as _new_; for, long before man appeared on this earth, the vegetation was collecting and condensing those ordinary natural powers which we find in fuel. In our time, too, the rains and dews, heat, motion, and gaseous food, are being stored up in a wondrous manner, to serve as elements of power which may be used and applied now or hereafter. In this view, too, we may include the winds, the falling of rain, the ascent and descent of sap, the condensation of gases,--in short, the natural powers, exerted before,--as the cause of motion in the steamboat.