320 Introduction to the Study of Science 



to higher speed and for a less load. They may haul a trailing 

 load of 800 tons on the grades at a speed of 20 to 25 miles an 

 hour, and on level stretches at a speed of 60 miles per hour. 



Comparison with steam locomotive. The steam locomotives 

 replaced by the electric locomotives are of the large Mallet 

 duplex or two-engines-in-one type. They weigh 6 per cent 

 more than the electric, and have a tractive effort of only 76,200 

 pounds, gr nearly 9000 less than that of the electric locomotives. 

 They are rated below the electric in speed and flexibility for 

 emergencies. Compare the weight and tractive effort of the 

 Erie engine (page 292). 



Electric current used. The motors make use of direct current 

 electricity at approximately 3000 volts. Alternating current 

 at 100,000 voltage is transmitted from the hydro-electric plants 

 of the Montana Power Company, the principal plant being 

 located at Great Falls, north of Helena, Montana, to the rail- 

 way's sub-stations, where it is stepped down by transformers 

 to 2300 volts and converted into direct current. It is dis- 

 tributed to the trolley wires and collected by the pantagraph 

 for the motors. In a complete locomotive there are eight 

 motors which are twin-geared to each of eight pairs of fifty- 

 two inch driving wheels (Fig. 99). 



Future use of electricity. The change of steam railroads into 

 electrically operated railroads is largely for purposes of economy. 

 It promises much as to the future use of electric power in trans- 

 continental traffic. It means the utilization of falling water now 

 running to waste and the economy of the coal resources of the 

 country. Twenty years will witness extensive transformations 

 of the present means of transportation with the probability of 

 electric energy taking precedence over steam. Even in those 

 cases where steam railroads have been electrified with energy 

 derived from heat from fuel, the railroads seem to yield financial 

 profit as well as other kinds. Such returns make it probable 

 that many similar installations will be made. 



Progress in the use of electric energy in transportation may 



