After these well-devised and truly scientific investigations, Watt was enabled to enter upon his work of improving the steam-engine with an intelligent understanding of its existing defects, and with a knowledge of their cause. Watt soon saw that, in order to reduce the losses in the working of the steam in the steam-cylinder, it would be necessary to find some means, as he said, to keep the cylinder "always as hot as the steam that entered it," notwithstanding the great fluctuations of temperature and pressure of the steam during the up and the down strokes. He has told us how, finally, the happy thought occurred to him which relieved him of all difficulty, and led to the series of modifications which at last gave to the world the modern type of steam-engine. He says:[37] "I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte street, and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that, as steam was an elastic body, it would rush into a vacuum, and, if a communication were made between the cylinder and an exhausted vessel, it would rush into it, and might be there condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet, as in Newcomen's engine. Two ways of doing this occurred to me: First, the water might be run off by a descending pipe, if an offlet could be got at the depth of 35 or 36 feet, and any air might be extracted by a small pump. The second was, to make the pump large enough to extract both water and air." "I had not walked farther than the Golf-house, when the whole thing was arranged in my mind." [37] "Reminiscences of James Watt," Robert Hart; "Transactions of the Glasgow Archæological Society," 1859. Referring to this invention, Watt said to Prof. Jardine:[38] "When analyzed, the invention would not appear so great as it seemed to be. In the state in which I found the steam-engine, it was no great effort of mind to observe that the quantity of fuel necessary to make it work would forever prevent its extensive utility. The next step in my progress was equally easy--to inquire what was the cause of the great consumption of fuel. This, too, was readily suggested, viz., the waste of fuel which was necessary to bring the whole cylinder, piston, and adjacent parts from the coldness of water to the heat of steam, no fewer than from 15 to 20 times in a minute." It was by pursuing this train of thought that he was led to devise the separate condenser. [38] "Lives of Boulton and Watt," Smiles.