For nearly seventy-five years engines were everywhere built after the Newcomen pattern. Improvements in a small way were added now and then but no very important change was made until the latter part of the eighteenth century, when the steam-engine was made by James Watt practically what it is to-day. This great inventor spent years in making improvements upon Newcomen's engine (Fig. 9) and when his labors were finished he had done more for the steam-engine than any man who ever lived. We must try to learn what he did. We can learn what Watt did by studying Figure 10. Here P is a piston working in a cylinder A closed at both ends. By the side of the cylinder is a valve-chest C into which steam passes from the pipe T. Connecting C with the cylinder there are two openings, one at the top of the cylinder and the other at the bottom. The valve-chest is provided with valves which are worked by means of the rod F, which moves up and down with the beam B, thanks to Humphrey Potter for the hint. The valves are so arranged that when steam enters the opening at the top of the cylinder it is shut off from the opening at the bottom, and when it enters the opening at the bottom it is shut off from the opening at the top. When the opening at the bottom is closed the steam will rush in at the upper opening and push the piston downward; when the piston has nearly reached the bottom of the cylinder the upper opening will be closed and steam will rush in at the bottom of the steam chest and push the piston upwards. Here was one of the things done by Watt for the engine: he contrived to make the steam push the piston down as well as up. You have observed that in Newcomen's engine steam was used only to push the piston up, the atmosphere being relied upon to push it down. Thus we may say that Watt's engine was the first real steam-engine, for it was the first that was worked entirely by steam. All engines before it had been worked partly by steam and partly by air.
Watt's greatest improvement upon the steam-engine is yet to be mentioned. In Newcomen's engine when the cold water was injected into the cylinder it cooled the piston and when steam was let into the cylinder again a part of it, striking the cold piston, was condensed before it had time to do any work and the power of this part of the steam was lost. Watt did not allow the piston to get cold, for he did not inject any cold water into the cylinder. In his engine as soon as the steam did its work it was carried off through the pipe M to the vessel N and there condensed by means of a jet of water which was injected into N (called the condenser) by means of a pump E worked by the motion of the beam, thanks again to Humphrey Potter for the idea. This condensation of the steam outside of the cylinder and at a distance from it prevented the piston (and cylinder) from getting cold. In other words, in the Watt engine when steam entered the cylinder it went straight to work pushing the piston. No steam was lost and no power was lost and the cost of running the engine was greatly reduced.
It cannot be said that Watt invented the steam-engine—no one can claim that honor—yet he did so much to make it better that he well deserves the epitaph which is inscribed on his monument in Westminster Abbey. This inscription is as follows:
NOT TO PERPETUATE A NAME
WHICH MUST ENDURE WHILE THE PEACEFUL ARTS
FLOURISH
BUT TO SHEW
THAT MANKIND HAVE LEARNT TO HONOR THOSE
WHO BEST DESERVE THEIR GRATITUDE
THE KING
HIS MINISTERS AND MANY OF THE NOBLES
AND COMMONERS OF THE REALM
RAISED THIS MONUMENT TO
JAMES WATT
WHO DIRECTING THE FORCE OF AN ORIGINAL
GENIUS
EARLY EXERCISED IN PHILOSOPHIC RESEARCH
TO THE IMPROVEMENT OF
THE STEAM ENGINE
ENLARGED THE RESOURCES OF HIS COUNTRY
INCREASED THE POWER OF MAN
AND ROSE TO AN EMINENT PLACE
AMONG THE MOST ILLUSTRIOUS FOLLOWERS OF
SCIENCE
AND THE REAL BENEFACTORS OF THE WORLD
BORN AT GREENOCH MDCCXXXVI
DIED AT HEATHFIELD IN STAFFORDSHIRE
MDCCCXIX
But the story of the steam-engine does not end with Watt. It will be remembered that in the engines of Nero and of Branca the steam did its work by reaction or by impulse. Now soon after the time of Watt, inventors turned their thoughts to the old engines of Nero and Branca and began to experiment with engines that would do their work by a direct impact of steam. After nearly a century of experimenting and after many failures there was at last developed an engine known as the steam-turbine. In this engine the steam does its work by impinging or pushing directly upon blades (Fig. 11) which are connected with the shaft which is to be turned, and it does this in much the same manner that we saw the steam do its work in Branca's engine. One of the greatest names connected with the steam turbine is that of Charles Algernon Parsons of England. In 1884 this great inventor patented a steam-turbine which proved to be a commercial success and since that date the steam-turbine has been constantly growing in favor. So great has been its success on land and on sea that there are those who believe that the engine invented by Watt will in time be cast aside and that its place will be taken by an engine which is the most ancient as well as the most modern of steam motors.