f= hs Oe 
4 
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 which 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 being condensed on the refrigerated surface of 
the body of the engine. 
Still another invention by Watt deserves a word, the 
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, 
