296 THE FIRE-ENGINE 



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motion of the piston water is drawn from the suction- 

 pipe into the pump-barrel, and at each downward 

 motion it is forced from the pump-barrel into the force- 

 pipe. It is evident that water may thus by adequate 

 pressure be forced to any height to which the force- 

 pipe reaches. Every point of the lever S, by means oi 

 which the piston-rod is moved, obviously describes an 

 arc of a circle, of which the fulcrum, which is at o: 

 end, is the centre. In order that the rod s may adap 

 itself to this circular motion, it is attached to the pistoi 

 by a hinge c, about which it can turn freely. 



In many practical applications of the forcing-pump 

 for example in the fire-engine, a continued flow of wate 

 is produced by means of an air-vessel, which acts in th 

 manner of the flask, fig. 169, p. 246. 



Fig. 197 (in which, as in fig. 195, the various part 

 are somewhat out of proportion) gives a sections 



FIG. 197. 



diagram of the fire-engine. This is a double forchi 

 pump, each barrel of which acts in the manner e: 

 plained above, the piston-ro cfs being worked by 

 doable lever, so that one piston is raised while the oth 1 



