THE LOCOMOTIVE. 



31. Another cause wliicli renders it necessary at certain points 

 of the line to keep engines waiting with their steam up, is the 

 existence of exceptional gradients. 



Thus, if a railway be generally laid out with gradients of about 

 15 feet a mile, but at a particular point a natural elevation of the 

 ground, or other cause, renders the construction of a gradient 

 rising at the rate of 60 feet a mile necessary, then the engines 

 which are adapted to the general character of the line become in- 

 sufficient for such exceptional gradient ; and, in such case, the 

 expedient resorted to is to keep one or more powerful engines con- 

 stantly waiting with their steam up at the foot of the incline, for 

 the purpose of aiding in propelling the trains in their ascent. 



These engines are denominated Assistant Engines or Bank 

 Engines. Their mode of operation is as follows. They wait near 

 the foot of the incline in a siding provided for the purpose ; and 

 when a train arrives and begins to ascend, the assistant engine 

 follows it, and, pushing from behind, aids the regular engine in 

 front in propelling it up the plane. When it arrives at the summit, 

 the assistant engine drops off, and, descending the plane, returns 

 to its station. 



32. It appeared from calculations, based on the preceding 

 principles, which I made some years since, that on the Belgian 

 lines the average distance run by each engine lighted was 78 

 miles, and on some of the French lines 76 miles. It also appeared 

 that each engine lighted was kept seven and a half hours standing 

 with steam up, including, of course, the reserve engines. Thus, 

 it follows, that for every ten miles over which an engine works, 

 it is kept an hour standing. 



33. The fuel consumed in working a railway may be classed 

 under three heads : 



1st. That which is consumed in lighting the engines and raising 

 their steam, to prepare them for work. 



2nd. That which is consumed while the engines stand with 

 their steam up, waiting for the trains they are intended to draw, 

 or standing in reserve, prepared for the contingency of accidents 

 on the line. 



3rd. That which is consumed in drawing the trains. 



"When the engine has stopped work, its fire-box is cleared, pre- 

 paratory to the engine being cleaned. A certain portion of coke, 

 more or less, according to the state of the fire-box at the moment 

 the engine is stopped, is collected in this way half consumed. 

 This coke is to a certain extent available to aid in lighting the 

 engine when next started. The small coke which has been 

 rejected as unfit for the working engine is mixed, in a greater or 

 less proportion, by the engineer with the large coke used for 

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