320 CHEMICAL MANURES. 



and on this stair the car is not driven by its own motor. A special 

 system consisting of a motor and a chain or cable, running above the 

 rail on the stair, pulls the car along in the following manner : A hook 

 fixed in the car catches the chain which drives the fixed motor of 

 the stair. The carrying system is drawn up to the moment when 

 the hook quits it, which happens when the car reaches the ele- 

 vated part or bearings. When the car catches on the stair the 

 current from its own motor ceases, whilst it puts the cable in 

 motion by means of another special motor which animates it with 

 a uniform motion. At the moment when the car reaches the 

 upper extremity of the inclined section, the inverse occurs. This 



Fig. 58. — Electric Automotor Truck. 



manner of traversing the stair is very advantageous ; it permits a 

 low-power motor to be used on the car. If the car motor had to 

 ascend a considerable incline of itself, it would require to have a 

 much greater force, hence a considerable weight increase of the 

 section of the carrier, and consequently an increase of expense in 

 the initial installation and working expenses (it would require in fact 

 motors six to ten times more powerful per car). There are cases, 

 however, where in consequence of considerations special to the 

 problem to be solved, it is preferred instead of this mixed solution 

 to solve the problem of removing material by means of indepen- 

 dent arrangements enabling each to surmount the difficulties en- 



