All About Engines

James Watt: The Man and his Work 41 of tin plate with a pump in it, and immersed this in cold water as shown in Fig. 16. He hung a weight on to the piston rod, got up steam in the boiler, and passed it through the cylinder until the latter was hot and free from air, and then made a few strokes with the pump to draw a little of the steam into the condenser. At once the piston rose sharply, lift- ing as it did so the weight of 18 lb. The problem was solved ! The pump required very little power, and could easily be worked by the engine itself. Instead of spraying water into the cylinder, the water could be sprayed into a separate vessel, a condenser, into which the steam could be drawn from the cylinder by a pump. Moreover, why should not the cylinder be kept hot by making it with double walls and providing it with a jacket of steam ? These and many other improvements soon occurred to Watt, but the first problem was to make a full-sized engine in order to convince people of the value of his invention. The construction of a full-sized engine, how- ever, was a more difficult task than he had yet essayed. His own experience had been in light metal work ; there were very few skilled mechanics in Scotland and, above all, there was need for secrecy, lest someone should rob him of the benefits of his invention. Watt started to make an engine with a cylinder 6 inches in diameter and 24 inches stroke, working first in a cellar and, later, in a disused pottery works. He could not get the cylinder cast, and would have had no means of boring it had he been