THE STEAM-ENGINE. 



503 



Fig. 57. 



at the same level as the water in the boiler, since the lower part has a free 

 communication with that water, while the surface is submitted to the pressure 

 of the same steam as the water in the boiler. This and the last-mentioned 

 gauge have the advantage of addressing the eye of the engineer at once, with- f 

 out any adjustment ; whereas, the gauge-cocks must be both opened, whenever 

 the depth is to be ascertained. 



These gauges, however, require the frequent attention of the engine-man ; 

 and it becomes desirable either to find some more effectual means of awaken- 

 ing that attention, or to render the supply of the boiler independent of any at- 

 tention. In order to enforce the attention of the engine-man to replenish the 

 boiler when partially exhausted by evaporation, a tube was sometimes inserted 

 at the lowest level to which it was intended that the water should be permit- 

 ted to fall. This tube was conducted from the boiler into the engine-house, 

 where it terminated in a mouth-piece or whistle, so that whenever the water 

 fell below the level at which this tube was inserted in the boiler, the steam 

 would rush through it, and issuing with great velocity at the mouth-piece, 

 would summon the engineer to his duty with a call that would rouse him even 

 from sleep. 



In the most effectual of these methods, the task of replenishing the boiler 

 should still be executed by the engineer ; and the utmost that the boiler itself 

 was made to do, was, to give due notice of the necessity for the supply of 

 water. The consequence was, among other inconveniences, that the level of 

 the water was subject to constant variation. 



To remedy this, a method has been invented, by which the engine is made 

 to feed its own boiler. The pipe G, fig. 58, which leads from the hot-water 



pump, terminates in a small cistern C in which the water is received. In the 

 bottom of this cistern, a valve V is placed, which opens upward, and commu- 

 nicates with a feed-pipe, which descends into the boiler below the level of the 





