a SS 
MODE OF REFRIGERATING. 885 
counterpoise. In the English machine, in short, in imi- 
tation of Papin’s, as soon as the piston has reached its 
maximum of ascent, the steam that had tended to push it 
there is refrigerated ; thus a vacuum is created through- 
out the space that the piston had traversed, and the ex- 
ternal atmosphere forces it to descend again. 
To obtain the requisite refrigeration, we already know 
that Papin contented himself with removing the chafing- 
dish that heated the base of the little metallic cylinder. 
Newcomen and Cawley had recourse to an arrangement 
far preferable in every respect: they poured an ample 
quantity of cold water into the circular space contained 
between the outer surface of the cylinder of their ma- 
chine and the internal surface of a second rather larger 
cylinder, which served as an envelop to the first. The 
cold was gradually communicated through all the thick- 
ness of the metal, and lastly reached the steam itself.* 
Papin’s machine, thus perfected as to the manner of 
cooling or condensing the steam, excited the proprietors 
of mines to the highest pitch. It spread rapidly through 
several counties of England, and rendered great service. 
The slowness of its movements, the necessary conse- 
quence of the tardiness with which the steam cooled and 
lost its elasticity, was still a subject of great regret. 
Chance fortunately indicated a very simple way of obvi- 
ating this impediment. 
At the beginning of the eighteenth century the art of 
casting metallic cylinders, and of hermetically sealing 
* Savery had already adopted throwing cold water on the ezterior 
surface of a metal vase, to condense the steam within it. This was 
the origin of his partnership with Newcomen and Cawley; yet we 
must not forget that Savery’s patent, his machines, and the work in 
which he describes them, are posterior by several years to Papin’s 
memoirs. 
SEC. SER. 17 
