Like all great discoveries, that of the motive power of steam, and the important uses to which it might be applied, was the work, not of any one mind, but of several minds, each borrowing something from its predecessor, until at last the first vague and uncertain Idea was developed into a practical Reality. Known dimly to the ancients, and probably employed by the priests in their juggleries and pretended miracles, it was not till within the last three centuries that any systematic attempt was made to turn it to useful account. But before we turn our attention to the persons who made, and, after many failures and discouragements, _successfully_ made this attempt, it will be advisable we should say something as to the principle on which their invention is founded. The reader knows that gases and vapours, when imprisoned within a narrow space, do struggle as resolutely to escape as did Sterne's starling from his cage. Their force of pressure is enormous, and if confined in a closed vessel, they would speedily rend it into fragments. Let some water boil in a pipkin whose lid fits very tightly; in a few minutes the vapour or steam arising from the boiling water, overcoming the resistance of the lid, raises it, and rushes forth into the atmosphere. Take a small quantity of water, and pour it into the hollow of a ball of metal. Then with the aid of a cork, worked by a metallic screw, close the opening of the ball hermetically, and place the ball in the heart of a glowing fire. The steam formed by the boiling water in the inside of the metallic bomb, finding no channel of escape, will burst through the bonds that sought to confine it, and hurl afar the fragments with a loud and dangerous explosion. These well-known facts we adduce simply as a proof of the immense mechanical power possessed by steam when enclosed within a limited area. Now, the questions must have occurred to many, though they were themselves unable to answer them,--Why should all this force be wasted? Can it not be directed to the service and uses of man? In the course of time, however, human intelligence _did_ discover a sufficient reply, and _did_ contrive to utilize this astonishing power by means of the machine now so famous as the Steam Engine.