Applied Science 805 



from rest increases its speed by from two-fifths to half a mile 

 per hour every second ; whereas an electric train accelerates from 

 a mile to a mile and a third per hour per second, and at the end 

 of half a minute will be travelling at 30 to 40 miles per hour. 

 This quick acceleration is exactly what is wanted in urban and 

 suburban areas, where stops are frequent and traffic heavy, as it 

 means a much higher average speed, shorter intervals between 

 trains, and a great increase in the carrying capacity of a line. 

 Actual figures show that schedule speeds on lines converted from 

 steam to electric traction have risen by 20 to 50 per cent. During 

 its operation by steam the London District Railway carried a 

 maximum of eighteen trains per hour on a track, whereas the 

 present electric trains run at intervals of about one and a half 

 minutes, or forty-two in the hour, at the busiest times of the day. 

 The suburban electric train dispenses with a separate loco- 

 motive, because the motors driving it are distributed among the 

 coaches. There are usually two motors, each of 200 horse-power, 

 under every other coach, so that a six-car train has a propelling 

 power totalling 1,200 horse-power. The distribution may be even 

 more generous, but in any case the electric train is more highly 

 "powered" than the steam train of equal length, and it must be 

 so to negotiate at high speed the heavy gradients which engineers 

 nowadays do not hesitate to include in an electrified track, though 

 they would be rigorously excluded from a new steam-operated 

 railway. The multiple-unit system, as it is called, of train con- 

 trol enables any number of coaches to be coupled together with- 

 out reducing speed capacity, as each unit contributes its proper 

 proportion of power. At the same time all the motors are as 

 fully under the driver's control as they would be if concentrated 

 in the locomotive. 



Powerful Electric Motors 



A very large part of the electrical energy generated by the 

 machines ultimately finds its way to electric motors, whereby it 



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