One day a lonely prisoner sat meditating in his cell in the Tower of London. He was a Marquis of Worcester, a nobleman of high rank and large fortune, who had been imprisoned for a political offense. But he had always been a mechanic, and had passed the happiest hours of his life in his workshop. As he watched, sad and almost hopeless in his prison, he noticed that the cover of a kettle that was boiling on the fire was raised up, and that a cloud of vapor escaped.

He examined the curious fact, and at last asked himself, What is it that lifts the cover?—what power is there hidden in the boiling kettle? It was evidently the white vapor; it was steam. The Marquis of Worcester had made a wonderful discovery, and when he was liberated he gave much of his time to the study of the new power. He felt the great value of steam to mankind; and in his work, A Century of Inventions, thanked God that he had been permitted to discover one of the "secrets of nature."

No one before him seems ever to have thought of making steam useful. The white vapor had risen from every boiling vessel since the first use of fire. It was familiar to the Jew, Assyrian, Greek, and Roman. A Greek man of science was even acquainted with some of its powers, and employed it to frighten one of his neighbors for whom he had no good-will. He placed a boiler in his cellar, and drove the steam through pipes around his neighbor's house, shaking it with a loud noise.

But no one had thought of confining the vapor in a pipe, and making it labor. No one in Shakspeare's time had fancied that there was a giant strength in boiling water; no one foresaw in 1660 that all the chief labors of the future would be carried on by the aid of a boiling kettle. But soon the idea suggested by the Marquis of Worcester seems to have excited the curiosity of other intelligent men. He left no machine behind him, if he had ever made one. His only object was to force up water. He wrote an account of his machine in 1663, and soon after died. In 1681, Morland used steam to raise water. Its power began to be discovered; it would burst, it was said, a gun, and inflict serious injuries.

Next, about 1687, Papin, a French Huguenot exiled to London, almost invented a real steam-engine. He filled a pipe or cylinder half full of water; a piston or rod of iron rested on the water. A fire was kindled underneath, the water boiled, the steam drove the piston to the top of the cylinder, where it was secured by a peg or latch. The fire was then taken away, the cold once more condensed the steam into water, the latch was let loose, and the piston descended to its former position. Papin in this way raised a weight of sixty pounds. He was full of ardor, believed that he could raise ten thousand pounds, and even suggested a steamboat.

But as yet the rude machine consisted only of a pipe, a piston, and a latch that was moved by an attendant. Soon after, in 1696, Savery invented the first real steam-engine. It consisted of two boilers, a cylinder, a stream of cold water to condense the steam, and was intended to pump water into cities, houses, and ships. Savery addressed his pamphlet describing his engine to King William, who had examined his machine with interest at Hampton Court. In the year 1700 the steam-engine was in its infancy.

It grew slowly. Savery's engine was improved, but was still for nearly a century imperfect and almost useless. It could only move a piston or rod up and down. No one had yet discovered a way to make it turn a wheel. Until the American Revolution, and the age of Washington and Franklin, the imperfect machine seemed of little real value.

James Watt, a young Scotch mechanic, almost made it what it is. He is the author of the modern steam-engine. He was the son of a maker of mathematical instruments. He was sickly, studious, and always fond of mechanical contrivances; at six years old he is said to have worked out problems in geometry in the sand; at fourteen he made an electrical machine; and at fifteen, Arago tells us, studied the steam that came from a tea-kettle, and planned some of his future labors. He was born in 1736.

His chief discovery was how to make the piston turn a wheel, and this he did by using the crank. His machines became capable of turning mills, moving spindles, and pumping out mines. He founded a great factory of steam-engines that were sold all over the world; he grew wealthy, famous, and was always benevolent. He never ceased to invent, write, and labor, even in extreme old age, and at eighty-three produced a new copying machine that imitated any piece of sculpture. Soon after he died. No one has done more to add to the comfort and ease of his fellow-men than Watt by his rare inventions.

The steam-engine is the finest example of the mechanical art. A thousand parts make up the whole, all of which move together in harmony. The most violent storm never disorders them. The piston moves, the crank turns, the steam rises, and is condensed. It is nothing but the Marquis of Worcester's kettle boiling over, Papin's rod or piston, Watt's crank, improved by later inventors. Yet what a wonderful creature it is! how beautiful and complete!