There was one further step for Watt to take in the development of his invention. He wished a more powerful engine than his double-acting one, and so he produced the “compound” engine. This was really two engines, the cylinders and condensers of which were so connected that the steam which had been used to press on the piston of the first could then be used to act expansively upon the piston of the second, and in this way the second engine be made to work either alternately or simultaneously with the first. And this compound engine is practically the very engine that we have to-day. Improvements have been made, but they have been made in details. The piston-rings invented by Cartwright have prevented the escape of steam, and so permitted the use of a higher pressure than Watt could achieve, and the cross-head invented by Haswell has provided the piston with a better bed on which to rest and freed it from a certain friction. The firm of Boulton and Watt had a successful career, and in time the sons of the two partners took the latters’ places. Watt had occasion to protect his patents by a suit at law, but he was victorious in this, and by the time the patent rights had expired the firm had built up such a large business that it was safe from rivals. Confident of his son’s ability to carry on the business Watt at length retired, to busy himself in studying other inventions, to cultivate his garden, and to revisit familiar scenes in his beloved Scotland. The steam-engine had come to take its place in the great onward march of progress. Men were already at work planning to make it move cars across the land and ships upon the sea. It was to revolutionize the manufacture of almost everything; what men and women had done before by hand it was now to do, and, devised at first because of the great need of a new way to work the coal mines, it was to provide a motive power to accomplish all kinds of labor. Such is the story of how James Watt took Newcomen’s simple piston and cylinder and so harnessed steam that he could make it do the work he wanted. V ARKWRIGHT AND THE SPINNING-JENNY 1732-1792