THE CONQUEST OF TIME AND SPACE 



are of unequal diameter, so proportioned ''that the 

 steam at high pressure in the smaller cylinder exerts 

 upon the piston approximately the same force that is 

 exerted by steam at a lower pressure in the larger 

 cylinder. Steam is admitted first into the smaller 

 cylinder, where it expends a portion of its initial energy, 

 and then passes into the larger cylinder, where it per- 

 forms an equal amount of work by exerting a dimin- 

 ished pressure upon a larger surface. This is the prin- 

 ciple of compounding, the relative sizes and positions 

 of the cyhnders being varied according to the condi- 

 tions to be met by the engine, or the ideas of the de- 

 signer or builder, or of the purchaser. While in the 

 marine and stationary engine the compound principle 

 has been carried with success and economy to three 

 and four stages of expansion in the use of steam, it has 

 not been found practicable to go beyond two stages in 

 compound locomotives." 



In a pamphlet issued recently by one of the leading 

 locomotive works of the country, some points of in- 

 terest concerning the compound locomotive were stated 

 concisely as follows: 



"In stationary-engine practice the chief measure of 

 the boiler efficiency is the economical consumption of 

 coal. In most stationary engines the boilers are fired 

 independently, and the draft is formed from causes 

 entirely separate and beyond the control of the escape 

 of steam from the cylinders. Hence any economy 

 shown by the boilers must of necessity be separate and 

 distinct from that which may be effected by the engine 

 itself. In a locomotive, however, the amount of work 



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