Out of all his experiments two conclusions were drawn by him; first, that the lower the temperature of condensation of steam the more perfect the vacuum thereby formed; second, that the temperature of the cylinder should be as nearly as possible equal to that of the steam admitted to it. In Newcomen’s engine these two conditions were obviously incompatible, and the problem was,--how could they be reconciled? Early in 1765, while walking one Sunday afternoon in Glasgow Green the idea flashed upon him of condensing the steam in a separate vessel. The steam was generated in a separate vessel, why not produce the vacuum separately? With a view to trying this effect he placed a hollow air-tight chest beneath the steam cylinder, connected with it by a pipe having a stop-cock in it. This new or lower vessel was immersed in a cistern of cold water. Upon trial being made, it was found that by this simple contrivance as perfect a vacuum as desired was produced; the speed of the engine was greatly increased, the expenditure of fuel radically reduced, the walls of the steam cylinder were maintained at a high and constant temperature, and the whole arrangement promised great success. The new vessel Watt called a Condenser. Fresh difficulties now arose. As the engine worked, the condenser gradually filled with the condensed steam and had to be emptied periodically. The water in which it was immersed became so hot, by absorbing the heat of the steam, that it frequently required changing. Watt promptly called in aid two new auxiliaries, two organs whose motion was derived from the main beam of the engine: the Air Pump and the Circulating Pump. By these expedients the action of the condenser was rendered satisfactory, and an engine resulted which had a fuel-consumption less than half that of Newcomen’s engine.