48 THOMAS COMMERFORD MARTIN 



^heel being usually placed in front, verticalh% within con- 

 venient reach of the motorman, who is seated; in some loco- 

 motives, however, the controller and hand wheel arc placed 

 on the top of the locomotive, in a horizontal position. The 

 motors are usually geared to the truck axles by means of cut 

 steel gear wheels, and the traction wheels are shrunk and 

 keyed upon the truck axles, being placed either inside or 

 outside the locomotive frame. Electric headlights and 

 mechanical brakes are used. The current is taken from an 

 overhead copper trolley wire by a grooved brass trolley 

 wheel, mounted on a short, stout trolley pole, and conveyed 

 through the controller to the motors and back to the gener- 

 ators by means of the track rails, which are copper bonded, 

 in order to insure a return circuit of thorough conductivity. 

 A speed of from 6 to 10 miles per hour is usually made. 



Because of the limited dimensions of ordinary mine 

 entries and the light weight of rails, the 20 ton mining loco- 

 motive is about the largest that can be used to advantage. 

 Greater hauling capacity is sometimes needed, however, and 

 accordingly a double locomotive has been introduced, con- 

 sisting of two standard 13 ton mining locomotives, one of 

 which is provided with a 4 motor controller and a 4 motor 

 commutating switch, so that the complete machine is operated 

 from the one controller. Here again, mining practice har- 

 monizes with that obtaining in electric railway work in the 

 adoption of what is known as the multiple unit control, by 

 means of which the control of motors over a whole train of 

 vehicles can be brought to one point and there manipulated 

 by one motorman, instead of being distributed, with each 

 set under the control of a separate driver. 



Figures taken from various mines in the coal fields, and 

 compiled by Mr. F. J. Piatt, show a generally high degree 

 of efficiency in electric haulage. At the Green Ridge col- 

 liery, Scranton, Pa., the cost of haulage by mule power was 

 estimated at 7.15 cents per ton and the cost of electric haulage 

 at 2.76 cents, showing a saving by electric haulage of 4.39 

 cents. At the Sturges shaft of the New York and Scranton 

 Coal company the cost for haulage by mule power was esti- 

 mated at 6.58 cents per ton and the cost of electric haulage 



