3 6 HER OES OF INVENTION AND DISCO VER V. 



tvasteful one ; inasmuch as, every time it was repeated, it cooled 

 not only the steam, but the vessel also, which, therefore, had 

 again to be heated by a large expenditure of fuel before the 

 steam could be reproduced. Newcomen's method of injecting 

 the water into the cylinder was a considerable improvement on 

 this ; but it was still objectionable on the same ground, though 

 not to the same degree ; it still cooled not only the steam, on 

 which it was desired to produce that effect, but also the cylinder 

 itself, which, as the vessel in which more steam was to be im- 

 mediately manufactured, it was so important to keep hot. It 

 was also a very serious objection to this last-mentioned plan, 

 that the injected water itself, from the heat of the place into 

 which it was thrown, was very apt to be partly converted into 

 steam ; and the more cold water was used, the more considerable 

 did this creation of new steam become. In fact, in the best of 

 Newcomen's engines, the perfection of the vacuum was so 

 greatly impaired from this cause, that the resistance experienced 

 by the piston in its descent was found to amount to about a 

 fourth part of the whole atmospheric pressure by which it was 

 carried down, or, in other words, the working power of the 

 machine was thereby diminished one-fourth. 



After reflecting for some time upon all this, it at last occurred 

 to Watt to consider whether it might not be possible, instead 

 of continuing to condense the steam in the cylinder, to contrive 

 a method of drawing it off, to undergo that operation in some 

 other vessel. This fortunate idea having presented itself to his 

 thoughts, it was not very long before his ingenuity also suggested 

 to him the means of realising it. In the course of one or two 

 days, according to his own account, he had all the necessary 

 apparatus arranged in his mind. The plan which he devised, 

 indeed, was an extremely simple one, and on that account the 



