6i8 THE POPULAR SCIENCE MONTHLY. 



hydraulic pressure admitted to the under side of the piston. This 

 pressure is derived simply from the water in the penstock sup- 

 plied to the turbine, and when the latter is working under full 

 gate that is, is taking water to its full capacity the pressure in 

 the penstock is decidedly less, just as the pressure in a water pipe 

 is partly relieved by the opening of a faucet. This causes the 

 supporting force on the under side of the piston to materially de- 

 crease, and a thrust bearing that is, a bearing adapted to with- 

 stand either pressure or pull, so as to hold the shaft against the 

 tendency to end play has to be resorted to in order to take up 

 the difference. As a matter of fact, the difference between the 

 supporting force when the flow is a minimum and that when the 

 gate is wide open is about two tons in the seventy-six. The way 

 this is handled is to arrange the area of the piston and the depth 

 below^ the upper water level so that at minimum flow the support- 

 ing pressure will be about one ton more than the total weight, 

 and at full gate about the same amount less. At the normal 

 rate of working there is very little to be taken up by the thrust 

 bearings. 



An idea of the magnitude of the proportions of the generators 

 may be gathered from the fact that the designers were limited in 

 the size of base plates that they could use by the inability of the 

 railways to transport, even by especially large and powerful cars, 

 pieces of proportions originally designed from the factories to 

 he falls. 



It is stated that, had it not been for the tariff restrictions im- 

 posed on the importation of electrical machinery, the generators 

 would probably have been purchased abroad. As it was, they, as 

 well as the motors which will operate on their circuits, are the 

 work of a great Pittsburg company. In the case of the turbines 

 the design was by a Geneva firm, and the construction mainly 

 done in Philadelphia. Certain of the fittings are French, and the 

 governors Swiss. 



One of the details in the power house is a traveling crane 

 capable of handling pieces weighing up to fifty tons, which com- 

 mands every portion of the floor of the building. The presence 

 of this piece of apparatus is of the greatest importance in the 

 case of anything going wrong with one of the generators or tur- 

 bines. With its assistance any portion of either of these ponder- 

 ous pieces of mechanism which may need repair can be moved 

 with the greatest expedition, and a spare interchangeable part 

 put in its place. Frequently in an installation of heavy ma- 

 chinery, although perhaps much less ponderous than these in 

 question, a break occurs which may cause a shut-down of many 

 hours, when, if sufficiently powerful means of moving heavy 

 parts were at hand, the damaged piece could be replaced in a 



