We travel by the aid of steam-power, and we think and speak of a locomotive or a steamboat as we once thought and spoke of a horse or a man; and no little feeling of self-sufficiency is engendered by the conclusion that this new source of power has been brought under control and put to work in our day. It is also true that we do not always entertain the most correct view of what we term the new power of locomotive and steamboat; and as it may aid us in some further steps connected with the subject of my remarks, a familiar object, such as a steamboat, may be taken as illustrative of the application of power, and we may thus obtain some simple ideas of what power truly is, in Nature. 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!