THE STEAM-ENGINE. 245 



the feed-pipe of the boiler. Warm water is thus con- 

 stantly supplied to the boiler, and effects a great sav- 

 ing of fuel. 



The supply of steam and the motion of the engine 

 are regulated by the governor^ Gr. "When the motion 

 is too fast, the two suspended balls, which revolve on 

 a vertical or upright axis, and which hang loosely like 

 pendulums, are thrown out from the axis, producing 

 the movement of a rod which shuts the steam-valve. 

 When the motion is too slow, the balls approach the 

 axis and open the valve. 



In high-pressure engines the steam is not condensed, 

 but escapes into the open air at every stroke of the pis- 

 ton, which produces the loud, successive puffs of all 

 engines of this kind. 



The steam-engine, in its most perfect form, is a 

 striking example of human ingenuity, and its qualities 

 are thus described by Dr. Arnott : "It regulates with 

 perfect accuracy and uniformity the number of its 

 strokes in a given time, and records them as a clock 

 does the beats of its pendulum. It regulates the quan- 

 tity of steam ; the briskness of the fire ; the supply of 

 water to the boiler ; the supply of coals to the fire. It 

 opens and shuts its valves with absolute precision as to 

 time and manner ; it oils its joints ; it takes out any 

 air accidentally entering parts which should be vacu- 

 ous ; and when any thing goes wrong which it can not 

 of itself rectify, it warns its attendants by ringing a 

 bell ; yet, with all these qualities, and even when ex- 

 erting a force of six hundred horses, it is obedient to 

 the hand of a child. Its aliment is coal, wood, and 

 other combustibles. It consumes none while idle. It 



