THE CONDENSER INTRODUCED. 391 



soon as it enters ; all the steam which before filled the 

 cylinder will be gradually annihilated ; the cylinder will 

 thus be cleared of steam without its sides being in the 

 least cooled, and the fresh supply of steam, with which 

 it will require to be filled, will not lose any of its elas- 

 ticity. 



The condenser attracts to itself all the steam contained 

 in the cylinder, partly because it contains some cold 

 water, and partly because is contains no elastic fluids ; 

 but as soon as some steam has been condensed, those two 

 conditions on which success depended have disappeared ; 

 the condensing water .has become hot by absorbing the 

 latent caloric of the steam ; a considerable portion of 

 steam has been generated at the expense of that hot 

 water ; the cold water contained besides some atmos- 

 pheric air which must have been disengaged during its 

 heating. If this hot water was not carried away after 

 each operation, together with the steam and the air con- 

 tained in the condenser, in the end no effect would be 

 produced. Watt, therefore, attains this triple purpose by 

 the aid of a common pump, called an air-pump, and the 

 piston of whicK carries a rod suitably attached to the 

 beam worked by the engine. The power intended to 

 keep the air-pump in motion, diminishes by that much 

 the power of the engine ; but it is only a small portion of 

 the loss that was occasioned, in the old arrangement, by 

 the steam beinsj condensed on the refrigerated surface of 



~D CJ 



the body of the engine. 



Still another invention by Watt deserves a word, the 



it 



advantages of which will become evident to everybody. 



When the piston descends in Newcomen's engine, it is 

 by the weight of the atmosphere. The atmosphere is 

 cold, hence it must cool the sides of the metal cylinder, 



