PNEUMATICS. 263 



mentum be not greater than that of a column of 

 water 33 feet high, having for its base the section 

 of the cylinder, and acting by the lever GH. 



In this way, an air-pump might be made to raise wa- 

 ter to any height whatever. But the production of 

 the vacuum by the mechanical means of valves and 

 pistons, from its difficulty and expence, could not 

 be reduced to practice. For this reason, recourse 

 is had to steam, which, from its facility of being 

 generated and destroyed, affords the means of pro- 

 ducing a vacuum over a great extent, and of renew- 

 ing it at pleasure. 



Suppose, therefore, the steam of water from a boiler 

 to be introduced through a valve into the cylinder, 

 and to expel the air ; and when this is done, the 

 valve to be shut, and another valve opened, by which 

 a jet of cold water is injected into the cylinder, the 

 steam will be quickly condensed ; a vacuum will be 

 produced, and the piston will be forced down by 

 the pressure of the atmosphere. 



The introduction of the steam at the bottom of the 

 cylinder will again elevate the piston, and the re- 

 production of the vacuum will cause the depression 

 of it ; so that the end of the lever to which W is 

 attached, may be employed to raise any weight, or 

 to pump up any quantity of water within certain 

 limits. This is the Steam Engine in its simplest 

 state. 



356. If 



