Engineers and their triumphs / the story of the locomotive, the steamship, bridge building, tunnel making

by F. M. Holmes

JAMES WATT.

The use of the steam expansively is to stop its rush to the cylinder when the piston has only partially accomplished its stroke, leaving the remainder of the stroke to be driven by the expansion of the steam. In early engines the steam was admitted by conical valves, worked by a rod from the beam. Murdock, we may add in parenthesis, is believed to have invented the slide-valve which came into use as locomotives were introduced, and of which there are now numerous forms. The valve is usually worked by an “eccentric” rod on the shaft of the engine.

Watt was the author of many other inventions and improvements of the steam engine. Indeed, although Savery and Newcomen and others are entitled to great praise, it was Watt who gave it life, so to speak, and made it, in principle and essence, very much that which we now possess. There have, indeed, been improvements as to the boiler, as to expansive working, and in various details, since his day; but, apart from the distinctive forms of the locomotive and the marine engine, the machine as a whole is in principle much as Watt left it.

The centre of all things in a steam engine is usually the cylinder. Here the piston is moved backward and forward, and thence gives motion as required to other parts of the machine.

The cylinder is in fact an air-tight, round box, fitted with a close-fitting, round plate of metal, to which is fixed the piston-rod. Now, it must be obvious that if the steam be admitted at one end of the cylinder it will, as it rushes in, push the metal plate and the piston outward, and if this steam be cut off, and the steam admitted to the other end of the cylinder, it will push the metal plate and piston back again.

But what is to be done with the steam after it has accomplished its work? It may be permitted to spurt out into the air, or into a separate vessel, where it may be condensed. In the locomotive, under Stephenson’s able handling, this escape of steam was created into a steam-blast in the chimney to stimulate the fire. In compound and triple-expansion engines the steam is used—or expanded, it is called—in two or three cylinders respectively. When steam is condensed, it may be returned to the boiler as water.

It was the repairing of a Newcomen engine that seems to have started Watt on his inventions and improvements of the steam engine. He was then a mathematical instrument maker at Glasgow. As a boy he had suffered from poor health, but had been very observant and studious; and it is said that his aunt chided him on one occasion for wasting time in playing with her tea-kettle. He would watch the steam jetting from its spout, and would count the water-drops into which the steam would condense when he held a cup over the white cloud.

Delicate though he was in health, he studied much, and came, indeed, to make many other articles besides mathematical instruments. When, therefore, the Newcomen engine needed repair, it was not unnatural that it should be brought to him. It appears to have been a working model used at Glasgow University. He soon repaired the machine; but, in examining it, he became possessed with the idea that it was very defective, and he pondered long over the problem—How it might be improved. What was wanting in it? How could the steam be condensed without cooling the cylinder?

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.”