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?