THE UTILIZATION OF NIAGARA. 227 



field is built up of thin sheets of mild steel. Along the edges of these 

 sheets are 187 rectangular notches to receive the armature winding, in 

 which the current is generated. This winding is in reality not a wind- 

 ing, as it consists of solid copper bars 1|4 by -^ inch, and there are two 

 of these bars in every square hole, packed in with mica as a precaution 

 against heating. These copper conductors are bolted and soldered 

 to V-shaped copper connectors, and are then grouped so as to form 

 two separate independent circuits. A pair of stout insulated cables 

 connect each circuit with the power-house switchboard. 



The rotating field magnet outside the armature consists of a huge 

 forged steel ring, made from a solid ingot of fluid compressed steel 54 

 inches in diameter, which was brought to a forging heat and then 

 expanded upon a mandril, under a 14,000-ton hydraulic press, to the 

 ring, 11 feet 7£ inches in diameter. On the inside of this ring are bolted 

 12 inwardly projecting pole pieces of mild open-hearth steel, and the 

 winding around each consists of rectangular copper bars incased in 2 

 brass boxes. Each pole piece, with its bobbin, weighs about 1^ tons, 

 and the speed of this mass of steel, copper, and brass is 9,300 feet, or 

 If miles per minute, when the apparatus is runniug at its normal 250 

 revolutions. Not until tbe ring was speeded up to 800 revolutions, or 

 6 miles per minute, would it fly asunder under tbe impulse of centrif- 

 ugal force. As a matter of fact, 100 revolutions is tbe highest speed 

 that can be attained. This revolving field magnet is connected with 

 the shaft that has to turu it, and is supported from above by a (i armed 

 cast-steel spider keyed to the shaft, this spider or driver forming a roof 

 or penthouse over the whole machine. Tbe shaft itself is held in 2 

 bearings inside the castings, around which the armature is built up, 

 and at the bearings is nearly 13 inches in diameter. At the lower end 

 is a flange fitting with tbe flange at the top of the turbine shaft, and at 

 the upper end is a taper, over which the driver fits. Tbe driver and 

 shaft have a deep keyway, and into this a long aud massive key fits, 

 holding them solidly together. The driver is of mild cast steel, having 

 a tensile strength of 74,700 pounds per square inch. Tbe bushings of 

 the bearings are of bronze, with zigzag grooves, in which oil under 

 pressure is in constant circulation. Grooves are also cut in tbe hub of 

 each spider to permit the circulation of water to cool the bearings, this 

 water coming direct from the city mains at a pressure of 60 pounds to 

 the square inch. Tbe oil returns to a reservoir, and is used over and 

 over again. Provision has been made against undue heating, and 

 plenty of chance is given for air to circulate. This is necessary, as 

 about 100 horsepower of current is going into heat, due to the lost mag- 

 netization of the iron and the resistance in the conductors themselves. 

 Ventilators or gills in the drivers are so arranged as to draw up air 

 from tbe base of the machine and eject it at considerable velocity, so 

 that whatever heat is unavoidably engendered is rapidly dissipated. 



In almost all electrical plants tbe switch board is a tall wall or slab 



