RESERVE ENGINES. 



to a certain point, it would end in a total inability to move. The 

 durability of the engine, therefore, requires that its work should 

 be suspended before these causes of disability operate to an inju- 

 rious extent. 



When its labour ceases, the engine-cleaners, who are, as it were, 

 its grooms, clean out its fireplace, scrape its grate-bars and the 

 internal surface of the fire-box, clean out its tubes, tighten all its 

 bolts and rivets, oil and grease all its moving parts, and, in a 

 word, put it again into working order. 



29. The expense of cleaning an engine, and the cost of the fuel 

 consumed in lighting it and raising the steam, so as to prepare it 

 for propulsion, must necessarily be charged upon the mileage 

 which it performs ; and the cost of this mileage will therefore be 

 augmented in the inverse proportion of the ratio of the total 

 mileage of the engine to the number of times it has been cleaned 

 and lighted during the period of its service. It is therefore im- 

 portant, in the economy of the locomotive power, to ascertain with 

 precision the proportion which the mileage of the engines bears to 

 the number of times they have been cleaned and lighted. 



Hence appears the importance of the record above mentioned, 

 of the number of times each engine has been lighted and cleaned. 



To determine the average number of miles run by each engine 

 after such cleaning and lighting, it is only necessary to divide the 

 total mileage of the locomotive stock, or of each class of it, by the 

 total number of engines lighted ; the quotient will give the distance 

 run by each engine lighted. 



In the practical working of the locomotive stock, it inevitably 

 happens that engines, after they have been lighted, had their 

 steam raised and prepared for starting, have to stand, keeping 

 their steam up more or less time, waiting for trains which they are 

 to draw ; and thus an expense is incurred, not directly productive, 

 for fuel and wages. 



30. But, besides this, the service of the road requires that, at 

 certain stations, engines shall be kept waiting with their steam up 

 ready for work, for the mere purpose of providing for the contin- 

 gencies of the active service of the road. Thus, if an accident 

 occur to a train, by which the engine that draws it is disabled, 

 notice is sent forward by the electric telegraph, by signals or other- 

 wise, to the next engine station, summoning an engine to proceed 

 to the spot to take on the train. If an engine were not prepared 

 for such a contingency, with its steam up, the road would be ob- 

 structed for a considerable length of time by the train thus acci- 

 dentally brought to a stand. 



The engines thus kept prepared for accidents are called Reserve 

 Engines. 



187 



