308 POPULAR SCIENCE MONTHLY 



each turbine, under an effective head of about 140 feet, dashes against 

 the turbine blades, the water is disgorged into a subterranean tunnel 

 about 21 feet in height and over a mile in length, through which 

 the discharged water is conducted to the lower Niagara Eiver, just 

 below the abutment of the upper steel arch bridge. 



The turbines, by means of the shaft connection, cause the gen- 

 erators on the power-house floor to revolve at the rate of 250 revolu- 

 tions a minute and to develop a two-phase alternating current of 5,000 

 horse-power. 



Each generator with its connected turbine is entirely distinct from 

 the other generators and turbines, and can be stopped by shutting off 

 the water from the supplying penstock and by applying electrically 

 operated brakes. 



Practically, the whole tremendous weight of each generator, shaft 

 and turbine is sustained by the hydrostatic upward pressure of water 

 conveyed in separate pipes from the level of the intake canal to a 

 compartment of the turbine wheel-case where the water presses against 

 the lower surface of a disc secured to the shaft. 



To generate an electric current by dynamos a coil of wire must 

 cut the lines of magnetic force emanating from a magnetic field. It is 

 immaterial whether the coils of wire (or armature) revolve around the 

 magnetic field or the magnetic field revolves around the armature. 

 For mechanical reasons, however, all the great generators at Niagara 

 Falls are constructed so that their magnetic fields shall revolve about 

 the coils of wire (the armature). 



After the generators have developed the electrical energy the cur- 

 rent controlled by appropriate switching devices is transmitted to the 

 power tenants in the immediate vicinity and to the more distant 

 tenants in Buffalo, Lockport and elsewhere. Where power is delivered 

 to tenants within a short radius of the power plants, the current is 

 transmitted at the generator voltage, but where power tenants are 

 situated at such distances from the generators that electric current 

 could be transmitted only at considerable loss at the generator voltage, 

 it becomes necessary for economical transmission to increase or " step 

 up " the voltage of the current by passing the electrical flow through 

 transformers. A transformer by means of primary and secondary 

 coils of wire of different diameters wound around a laminated iron 

 core and with windings in a fixed ratio to each other may increase 

 or diminish the voltage of a current according as an increase or a 

 diminution of voltage may be necessary. The voltage of the current 

 delivered in Buffalo is about 22,000, but as it would be obviously 

 impossible to utilize so great a current pressure the electricity in Buf- 

 falo again passes through transformers where the voltage of the current 

 is reduced to that required in the electric light and electric car 

 service and for other power purposes. 



