2 4 HER OES OF INVENTION AND DISCO VER Y 



withdrawn from below it. Otto Guericke used to exhaust the 

 lower part of the cylinder, in such an apparatus, by means of 

 an air-pump. It appeared to Papin that some other method 

 might be found of effecting this end more expeditiously and 

 with less labour. First he tried to produce the requisite 

 vacuum by the explosion of a small quantity of gunpowder in 

 the bottom of the cylinder, the momentary flame occasioned 

 by which he thought would expel the air through a valve open- 

 ing upwards in the piston, while the immediate fall of the valve, 

 on the action of the flame being spent, would prevent its re- 

 intrusion. But he never was able to effect a very complete 

 vacuum by this method. He then, about the year 1690, be- 

 thought him of making use of steam for that purpose. This 

 vapour, De Cans had long ago remarked, was recondensed and 

 restored to the state of water by cold ; but up to this time the 

 attention of no person seems to have been awakened to the 

 important advantage that might be taken of this one of its 

 properties. Papin for the first time availed himself of it in his 

 lifting machine, to produce the vacuum he wanted. Introduc- 

 ing a small quantity of water into the bottom of his cylinder, 

 he heated it by a fire underneath, till it boiled and gave forth 

 steam, which, by its powerful expansion, raised the piston from 

 its original position in contact with the water, to a considerable 

 height above it, even in opposition to the pressure of the atmo- 

 sphere on its other side. This done, he then removed the fire, on 

 which the steam again became condensed into water, and, occupy- 

 ing now about the seventeen hundredth part of its former dimen- 

 sions, left a vacant space through which the piston was carried 

 down by its own gravitation and the pressure of the atmosphere. 

 The machine thus proposed by Papin was abundantly 

 defective in the subordinate parts of 'ts mechanism, and, unim- 



