*274

MOTIVE POWER EMPLOYED

load, more than what takes place in ordinaryengines of the same kind, except what aris-esfrom the causes hereinbefore explained.

The quantity of water used, as will be seenby the Tables VI. and VII. varies a little; theaverage will give about one gallon of waterfor every 3lbs. of coal.

As before stated, the true measure of effectis the quantity of work performed with a cer-tain weight of steam. Now, the weight ofsteam will be proportionate to the quantity ofcoals consumed, in all cases, unless some causeoperate in the interior arrangement of theengines, to produce an alteration in the law.The centrifugal force, produced by the pro-gressive motion of the engine, may, at suddenchanges in the velocity, cause a waste of water,by mixing it with the steam, and causing it topass in that state through the cylinders intothe atmosphere. This is frequently found tobe the case if the boiler contains more than anordinary quantity of water, and when the en-gine is commencing its motion ; but still thereappears an extraordinary waste of fuel com-pared with that consumed by the most econo-mical form of high-pressure engines, and it is tothis part of the internal construction of theengine that the great defect arises; and thatto which the attention of engineers, wishing to