CHAP. V.] 



THE STEAM-ENGINE. 



393 



M 



atmosphere, and advantage may be taken of this considerable pressure 

 to enable it to raise weights. 



In one word, the arrangement of Papin's machine is slightly 

 different from that in which Huygens made a vacuum by gunpowder, 

 but the effect produced is the same. Only it is steam that works 

 it, and its elastic force raises the piston, and its condensation by cold 

 makes the vacuum. 



Let us insist here upon two facts Papin in this original steam- 

 engine, employed at first the elastic fluid at a pressure a little greater 

 than that of the atmosphere ; he then made use of 

 it as a motive power to raise the piston, afterwards 

 he condensed it by cooling so as to make a vacuum, 

 and then the atmospheric pressure becomes the 

 true motive power, and accomplishes the work for 

 which the machine is constructed. Later he modi- 

 fied his first conception, but not happily, as we 

 must confess, and it is the engine just described 

 that constitutes his great title to honour, and 

 his incontestable right to be considered as the 

 inventor of the steam-engine. 



Papin first proposed to use his engine as a 

 pump ; for this purpose the water was admitted 

 by a suitable valve below the piston, steam was 

 then admitted above, and by its expansive force 

 drove the water up and out by the out-flow pipe. 

 His engine differed from the one subsequently sug- 

 gested by Savery mainly in the employment of the 

 piston, while the latter allowed the steam to come in contact with 

 the water, thus losing a great deal of power by condensation. Papin 

 later intended to employ his engine as a prime mover by causing the 

 water issuing from the cylinder to work a water-wheel. 



Both Savery and Papin got as far as producing the steam in one 

 vessel and using it in another, but it remained for Watt to make the 

 next most fundamental improvement, viz,, that of condensing in a 

 separate vessel, as well as separating the steam cylinder from the 

 pump-barrel. 



Although Savery conceived the happy idea of producing the 

 steam in one vessel and condensing it in another; yet his engine 



FIG. 272.- Papin's first 

 steam-engine. 



