HYDRAULICS. 215 



run out through the eduction-pipe, q, and, lifting 

 up the valve, r, flow into the hot-well. 



By the admission of the steam under the piston, 

 the pressure of the atmosphere on the top is coun- 

 terbalanced, and the piston is free to move up- 

 wards or downwards. 



But the other end of the beam being broader, so 

 as to be heavier than the piston, now raises it to 

 the top of the cylinder, whence it is again forced 

 downwards by the pressure of the atmosphere, as 

 soon as the vacuum is formed under it by the ad- 

 mission of the injection-water. In this manner the 

 operation is repeated ; the piston, being forced 

 down by the weight of the atmosphere, raises the 

 other end of the beam with whatever is attached 

 to it : and, on the other hand, when the pressure 

 of the atmosphere is counterbalanced by the steam 

 under the piston, the superior weight of the pump- 

 end of the beam brings the piston up again. 



Savary's was an engine that raised water by the 

 pressure of steam ; but Newcomen's raises water 

 entirely by the pressure of the atmosphere ; and 

 the steam is employed merely as the most expedi- 

 tious mode of producing a vacuum, into which the 

 atmospherical pressure may impel the first mover 

 of his machine. 



Hence the great superiority of this latter engine. 

 We have no need of steam of very great elasticity"; 

 and we operate by means of very moderate heats, 

 and, consequently, with much smaller quantity of 

 fuel. There are no bounds to the power of this 

 machine ; however deep a mine may be, a cylinder 

 may be used of such dimensions, that the pressure 

 of the air may exceed the weight of the column of 

 water to be raised. The form of this machine also 

 renders it applicable to almost every mechanical 



p 4 



