THE CONQUEST OF NATURE 



travels automatically when the current is turned on, 

 stopping when the current is cut off. This is quite a 

 common arrangement for smaller telphers, but in the 

 larger ones a man travels with the telpher and load, 

 controlling the train just as in the case of the ordinary 

 trolley system. 



The various processes of hoisting in mines by elec- 

 tricity is closely akin to that of traction, since, after all, 

 "an elevator is virtually a railway with a loo-per-cent 

 grade." As such work is done spasmodically, long 

 periods of rest intervening between actual periods of 

 work, a great deal of energy is wasted by steam hoisting 

 engines, where a certain pressure of steam in the boiler 

 must be maintained at all times. For this reason 

 electrical energy for hoisting has come rapidly into 

 popularity in recent years. "The throttling of steam 

 to control speed," said Mr. F. O. Blackwell in address- 

 ing the American Institute of Mining Engineers, "the 

 necessity for reversing the engine, the variation in steam 

 pressure, the absence of condensing apparatus, the 

 cooling and large clearance of cylinders, and the con- 

 densation and leakage of steam pipes when doing no 

 work, are all against the steam hoisting engine. One 

 of the largest hoisting engines in the world was recently 

 tested and found to take sixty pounds of steam per 

 indicated horse- power per hour. The electric motor, 

 on the other hand, is ideal for intermittent work. It 

 wastes absolutely no energy when at rest, there being 

 no leakage or condensation. Its efficiency is high, 

 from one-quarter load to twice full load." 



There seems to be practically no difference as far as 

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