192 future's 



its work it flows off through the tunnel into the 

 river below the falls. 



To the upper end of the power-shaft is at- 

 tached a great revolving umbrella-shaped 

 hood; to the periphery (circumference) of 

 this hood is attached a forged steel ring, 5 

 inches in thickness, about 12 feet in diameter 

 and from 4 to 5 feet in width. The whole of 

 the revolving portion including the ring upon 

 which are mounted the field-magnets, the 

 hood, and the shaft running to the bottom of 

 the pit, where the turbine wheel is attached 

 weighs about thirty-five tons. 



The dynamos belong to the alternating type, 

 and are comparatively simple in construction. 

 In a previous chapter upon the dynamo it was 

 stated that the fundamental feature was the 

 relation that the field-magnet and the arma- 

 ture sustained to each other, and that in some 

 cases the field-magnet revolves while the part 

 that is technically called the armature remains 

 stationary. In other cases the armature re- 

 volves and the field-magnets are stationary. 

 In the latter case brushes and commutators 

 are used, to catch and transfer the generated 

 electricity, while in the former these are not 

 needed, which simplifies the construction of 

 the machine. 



As we have stated, the dynamos used at 

 Niagara are constructed with revolving field- 

 magnets that are bolted on to the inner surface 



