My travelled friend considers a steamboat as a ship propelled by wheels, the shaft to which they are attached being moved by the machinery.  He follows back to the piston of the engine and finds the motor there,—­satisfied that he has discovered in the transference of rectilinear to rotatory motion the reason for the progress of the boat.  A more inquisitive friend does not rest here, but assumes that the power of the steam flowing through the machine sets in action its parts; and he rests from farther pursuit of the power, where the larger number of those who give any observation to the application of steam are found,—­gratified with the knowledge accumulated, and the readiness with which an explanation of the motion of the boat can be traced to the power of steam as its source.

We must proceed a little farther on our backward course from the point where the power is applied, and in our analysis consider the steam as only the vehicle or carrier of the power; and examining the conditions, we find that water acted on by fire, while contained in a suitable vessel, after some time takes up certain properties which enable it to go forward and move the ponderous machinery of the boat.  The water evidently here derives its new character 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.