212 THE POPULAR SCIENCE MONTHLY 



which these facts may go. A steam road in the middle west was paral- 

 leled by an electric line ; the latter took away over fifty per cent, of the 

 steam traffic and increased the total traffic fifteen times the original 

 amount within seven years. If we look for the reasons for such ad- 

 vantages in absorbing and promoting traffic we realize that electric 

 travel is faster, more frequent and more comfortable. It provides 

 freedom from smoke, better ventilation, easy regulation of light and 

 heat and in fact travel in many instances is actually a pleasure. 



While the public is appealed to as cited above, the operating and 

 transportation departments of the railroad are equally appealed to by 

 the methods afforded under electric operation for handling the resulting 

 increase in business. Present day steam service may be divided into 

 three broad classes: (1) Suburban and terminal; (2) long haul pas- 

 senger and express and (3) freight traffic. The advantages of elec- 

 tricity as motive power in all three of these classes of service are found 

 in the possibilities of obtaining more mileage and hauling capacity 

 from the equipment, the operation of more trains on the line at one 

 time and better operating conditions and consequent reliability. 



Figures have already been given showing the increased train capac- 

 ity of the several electric installations in and about New York city 

 and many other similar instances might be cited. These results are 

 largely due to the fact that an electric locomotive or train operates at a 

 higher schedule speed than is possible under steam. The elapsed time 

 of a suburban train between stops depends principally on the rapidity 

 with which it attains its maximum speed. The rate at which it 

 reaches this speed, that is, the acceleration, depends on the value of the 

 pull exerted by the motive power. During the period of starting the 

 greatest draw-bar pull is required, since during this time the inertia 

 of the mass of the train must be overcome. After reaching a maxi- 

 mum speed the only forces to be overcome are those of frictional re- 

 sistance of the track and the air. In a steam locomotive the greatest 

 draw-bar pull being required at starting, steam is admitted to the 

 cylinders throughout the full length of the stroke. The demand on 

 the boiler per revolution is, therefore, greatest at this time. No loco-, 

 motive can, on the average, exert a greater pull than 25 per cent, of 

 the weight carried by its own driving wheels, for beyond this figure the 

 wheels will slip on the track. The boiler capacity, therefore, is de- 

 signed to give no more steam than that demanded by this value of the 

 pull at starting. A steam train, therefore, does not utilize the weight 

 of its own cars as a means of increasing its grip on the rails. In a 

 multiple unit electric train, motors are placed on each car, thus utiliz- 

 ing the weight of the entire train for frictional adhesion to the rail. 

 By electric control of the motor switches all the motors may be oper- 

 ated simultaneously by one man at the head of the train. By this 



