812 The Outline of Science 



deep pits there, referred to in an earlier paragraph, has a large 

 upright barrel-like fixed chamber into which the penstock (steel 

 tubes) delivers the water under high pressure; and a vertical 

 shaft passing through the ends of the barrel, with two large disks 

 attached to it of larger diameter than the barrel. The disks are 

 outside and almost touching the ends, and round their circum- 

 ference are attached upright rings of vanes which overlap the 

 barrel, so as to be opposite rings of guide blades fixed in open- 

 ings near the barrel's ends. The water gushing outwards through 

 the guides strikes the wheel vanes at an effective angle and drives 

 the disks round and round, and the shaft with them. Outside the 

 moving vanes are solid rings which can be raised or lowered by 

 an automatic governor to regulate the rate of escape of the water 

 and the speed at which the turbine runs. 



The turbines in the power-houses below the Falls are differ- 

 ently arranged. They stand beside the generators on the same 

 floor, and their shafts are horizontal and short. The water enters 

 a ring-shaped chamber, open on its inner side, and passes through 

 guides on to the blades of an internal wheel, which alters the flow 

 of the water and discharges it in a direction parallel to the 

 shaft. 



Few of the Niagara turbines are of less than 5,000 h.p. ; 

 many develop 10,000 h.p.; and some of the latest 45,000 h.p. 

 Some of the generators which they drive are the largest yet built, 

 weighing 300-400 tons apiece. 



The Pelton Wheel, though not employed in the Niagara 

 plants, is widely used in power-stations for coupling to generators 

 where water is available at very high pressures. A wheel consists 

 of a large disk with pairs of cups distributed round its circum- 

 ference. A jet of water issuing at high velocity from a nozzle 

 strikes the knife-like division between a pair of cups, and is split 

 right and left into two streams which pass round the inside of 

 the cups, and by reversing their direction in doing so impart all 

 their energy to the cups, which travel forward at half the speed 



