2i6 THE POPULAR SCIENCE MONTHLY 



to be regarded that it is now often used for crossings of telegraph, tele- 

 phone and transmission wires in place of the usual cradle or network 

 of wires stretched between the two lines. The values of voltage now 

 advocated for railway and transmission work have caused considerable 

 criticism and opposition. This is probably due in large measure to the 

 long standing figure of 600 volts for trolley service; this figure, how- 

 ever, is fixed by the character of the direct current motor and not by 

 any consideration of possible danger from shock. A further source of 

 disturbance by electrical operation is the interference by electrostatic 

 and electromagnetic induction between the transmission conductors and 

 the telegraph and telephone lines in the vicinity. Methods have been 

 developed, however, and are at present in use by which such disturb- 

 ances are prevented at slight cost. 



A decrease in the operating expenses has already been stated as one 

 of the means by which electric operation may be made to pay. The 

 operating expenses of an average steam railroad may be roughly divided 

 as follows : Maintenance of way 21 per cent., maintenance of equipment 

 19 per cent., conducting transportation 56 per cent., general expenses 

 4 per cent. Considering these items under electric operation the great- 

 est saving is effected in the item of conducting transportation, which 

 includes the cost of coal. The steam locomotive consists of a boiler 

 and engine. For obvious reasons neither is as efficient as the same 

 apparatus of a stationary type. The same amount of coal in a locomo- 

 tive boiler will evaporate only about two thirds as much water as in a 

 stationary boiler. The average steam consumption of a good locomo- 

 tive engine is about 30 pounds of steam per horse power hour developed; 

 turbo-generators are now guaranteed for a consumption of only 15 

 pounds of steam per electrical horse power at the switchboard. As off- 

 setting these marked advantages it is necessary to consider the electrical 

 losses in the transmission system and in the motor equipments. Speak- 

 ing roughly, 75 per cent, of the electrical energy supplied by the 

 switchboard is available at the wheels of an electric train for tractive 

 effort. These figures indicate that an electric locomotive requires less 

 than one half the amount of coal used by the steam locomotive giving 

 the same horse power output. Further than this, it has been esti- 

 mated that for every hour that a locomotive is standing idle, with 

 steam up, 400 pounds of coal are burned. The excess of useless mileage 

 and the excess ton mileage owing to the greater weight of the steam 

 locomotive have already been noted, and are also causes for excess coal 

 consumption. As opposed to these, there is the light load coal con- 

 sumption of the power station. The final value of the balance in coal 

 saving will depend on the proportion of time in which the power sta- 

 tion operates to its full capacity. Based on careful comparative tests 

 of steam and electric locomotives the engineers of one of the large 



