Transportation on Land 



319 



cent. Here a pusher helps 

 over the steep grade, and at 

 the summit is transferred to 

 the head of the trains and 

 aids in retarding the speed 

 down grade. 



Regenerative braking. In- 

 stead of depending upon 

 brakes, involving wear and 

 tear of wheels, brake shoes, 

 and track, the motors of both 

 locomotives when going down 

 grade are changed into electric 

 generators which not only 

 brake the train effectually, 

 but also send into the trolley 

 25 to 50 per cent of the total 

 electric energy consumed. 

 The air brakes are used only 

 in stopping and in emergen- 

 cies. The important point 

 is that the motors are reversi- 

 ble in function (page 324). 

 When going up grade they 

 take in electrical energy and 

 give out mechanical energy 

 for hauling. When going 

 down grade they take in me- 

 chanical energy and give 

 out electrical energy. This 

 method of braking is known 

 as the regenerative. 



The passenger locomotives 

 are like the freight locomotive 

 except that they are geared 



