"It would be a terrible humiliation if I should discover that I could not do it, wouldn't it?" replied Mr. Tolman with a smile. "In point of fact, there actually is not a great deal more that it is essential for one to know. It was by perfecting the engines of the Newcomen type and adding to them first one and then another valuable device that Watt finally built up the forerunner of our present-day engine. The progression was a gradual one. Now he would better one part, then some other. He surrounded the cylinder, for example, with a jacket, or chamber, which contained steam at the same pressure as that within the boiler, thereby keeping it as hot as the steam that entered it--a very important improvement over the old idea; then he worked out a plan by which the steam could be admitted at each end of the cylinder instead of at one end, as was the case with former engines. The latter innovation resulted in the push and pull of the piston rod. So it went." "How did Watt come to know so much about engines?" asked Stephen. "Oh, Watt was an engineer by trade--or rather he was a maker of mathematical instruments for the University of Glasgow, where he came into touch with a Newcomen engine. He also made surveys of rivers, harbors, and canals. So you see it was quite a consistent thing that a man with such a bent of mind should take up the pastime of experimenting with a toy like the steam engine in his leisure hours." "Did he go so far as to patent it, Henry?" Mrs. Tolman questioned. "Yes, he did. Many of our scientists either had not the wit to do this, alas, or else they were too impractical to appreciate the value of their ideas. In consequence the glory and financial benefit of what they did was often filched from them. But Watt was a Scotchman and canny enough to realize to some extent what his invention was worth. He therefore obtained a patent on it which was good for twenty-five years; and when, in 1800, this right expired he retired from business with both fame and fortune." "It is nice to hear of one inventor who got something out of his toil," Mrs. Tolman observed. "Indeed it is. Think of the many men who have slaved day and night, forfeited health, friends, and money to give to the world an idea, and never lived to receive either gratitude or financial reward, dying unknown or entirely forgotten. There is something tragic about the injustice of it. But Watt, I am glad to say, lived long enough to witness the service he had done mankind and enjoy an honored place among the great of the world." "Is the kind of engine Watt invented now in use?" Doris inquired.