Suddenly, one day, so the story goes, the idea struck him, when loitering across the common with bent brows, that if steam were elastic, it would spurt into any vessel empty of air. Impatiently, he hastened home to try the experiment. He connected the cylinder of an engine with a separate vessel, in which the air was exhausted, and found that his idea was correct; the steam did rush into it. Consequently the steam could be condensed in a separate vessel, and the heat of the cylinder maintained and the loss of power prevented. This invention seems simple enough; yet it increased the power of an engine threefold, and is at the root of Watt’s fame. We must remember that the inventions which in process of time may appear the simplest and the most commonplace, may be the most difficult to originate. And it may fairly be urged—If it were so very simple, and so very obvious, why was it not invented before? The supposition is that in those days it was not so simple. It is possible that the great elasticity of steam was not sufficiently understood. In any case, the discovery and its application are regarded as his greatest invention. Yet ten years elapsed before he constructed a real working steam engine, and so great we may suppose were the difficulties he encountered, including poorness of health, that once he is reported to have exclaimed: “Of all things in the world, there is nothing so foolish as inventing.” But a brilliant triumph succeeded. Eventually Watt became partner with Mr. Matthew Boulton, and the firm of Boulton & Watt manufactured the engine at Soho Ironworks, Birmingham. Mining proprietors soon discovered the value of the new machine, and Newcomen’s engine was superseded for pumping. Watt continued to improve the machine, and together with Boulton also greatly improved the workmanship of constructing engines and machinery. In a patent taken out in 1784, he “described a steam locomotive”; but for some reason he did not prosecute the idea. It is possible that the notion of building a special road for it to run upon did not occur to him, or appear very practicable. His work was done, and it was a great work; but it was left for others to develop the steam engine into forms for hauling carriages on land or propelling ships upon the sea. Trevithick, Stephenson, and others did the one; Symington, Bell, and others did the second. Watt died in 1819, and though so delicate in youth, he lived to his eighty-fourth year. The steam engine, therefore, as Watt left it, was practically as Stephenson came to know it. He would be acquainted with it chiefly as a pumping machine. But he saw what others had done to adopt it as a locomotive, and he now set to work.