ELECTRICITY DURI:N^G THE NINETEENTH CENTURY. 851 



more from ii cit}^ or from a large manufacturing center where cost of 

 fuel i.s high may be utilized as follows: A power station will be 

 located upon the site of the water power and the dynamos therein will 

 generate electricity at, say, 2,000 volts pressure. By means of step-up 

 transformei's this will be exchanged for a current of 80,000 volts for 

 transmission over a line of copper or aluminum wire to the distant 

 consumption ai-ea. Here there will be a set of step-down transformers 

 which will exchange the 30,000 volt line current for one of so low a 

 pressure as to be safe for local distribution to lamps, to motors, etc., 

 either stationary or upon a railway. The same transmission plant 

 may simultaneously supply energ}' for lighting, for power, for heat, 

 and for charging storage batteries. It may therefore be eraplo3'ed 

 both day and night. 



These long-distance power-transmission plants are generally spoken 

 of as "two-phase,"' ''three-phase," or "polyphase" systems. Before 

 1890 no such plants existed. A large number of such installations are 

 now working over distances of a few miles up to 100 miles. They differ 

 from what are known as single-phase alternating systems in empWing, 

 instead of a single alternating current, two, three, or more, which are 

 sent over separate lines, in which the electric impulses are not simul- 

 taneous, but follow each other in regular succession, overlapping each 

 other's dead points, so to speak. Early suggestions of such a plan, 

 about 1880 and thereafter, b}^ Baily, Deprez, and others bore no fruit, 

 and not until Tesla's announcement of his polyphase system in 1S88 

 was much attention given to the subject. A widespread interest in 

 Tesla\s work was invoked, but several years elapsed before engineering 

 difficulties were overcome. This work was done mainly by the tech- 

 nical staffs of the large manufacturing companies, and it was necessary 

 to be done before any notable power transmissions on the polyphase 

 system could be established. After 1892 the growth became very rapid. 



The Falls of Niagara early attracted the attention of engineers to the 

 possibility of utilizing at least a fraction of the power. It was seen 

 that se^ eral hundred thousand horsepower might be drawn from it 

 without materially affecting the fall, itself equivalent to several millions 

 of horsepower. A gigantic power station has lately been established 

 at Niagara, taking water from a distance above the falls and deliver- 

 ing it below the falls through a long tunnel, which forms the tailrace. 

 Ten water wheels, located in an immense wheel pit about 200 feet deep, 

 each wheel of a capacity of 5,000 horsepower, drive large vertical 

 shafts, at the upper end of which are located the large two-phase 

 dynamos, each of 5,000 horsepower. The electric energy from these 

 machines is in part raised in pressure by huge transformers for trans- 

 mission to distant points, such as the city of Buffalo, and a large 

 portion is delivered to the numerous manufacturing plants located at 

 moderate distances from the power station. Besides the supply of 



