504 



THE STEAM-ENGINE. 



water in it. The stem of the valve V is connected with a lever turning on 

 the centre D, and loaded with a weight F dipped in the water in the boiler in 

 a manner similar to that described in fig. 56, and balanced by a counterpoise 

 A in exactly the same way. When the level of the water in the boiler falls,. ' 

 the float F falls with it, and pulling down the' arm of the lever raises the valve 

 V, and lets the water descend into the boiler from the cistern C. When the 

 boiler has thus been replenished, and the level raised to its former place, F 

 will again be raised, and the valve V closed by the weight A. In practice, 

 however, the valve V adjusts itself by means of the effect of the water on the 

 weight F, so as to permit the water from the feeding-cistern C to flow in a 

 continued stream, just sufficient in quantity to supply the consumption from 

 evaporation, and to maintain the level of the water in the boiler constantly the 

 same. 



By this arrangement the boiler is made to replenish itself, or, more properly 

 speaking, it is made to receive such a supply, as that it never wants replen- 

 ishing an effect which no effort of attention on the part of an engine-man 

 could produce. But this is not the only good effect produced by this contri- 

 vance. A part of the steam which originally left the boiler, and having dis- 

 charged its duty in moving the piston, was condensed and reconverted into 

 water, and lodged by the air-pump in the hot well, tig. 58, is here again re- 

 stored to the source from which it came, bringing back all the unconsumed 



Fig. 59; 



