6i6 THE POPULAR SCIENCE MONTHLY. 



each would have its own circuit, and, if it broke down, the whole 

 dependent system would be idle until repairs were completed. 

 One of the great aims of the company appears to be to insure the 

 permanence and continuousness of their power service which is, 

 of course, of the utmost importance to manufacturers. 



A remarkable method of construction not, however, unique 

 is employed in the generators to secure means for direct coupling 

 to the turbine shafts. These latter are vertical, and come up 

 over one hundred and forty feet out of the wheel pits from the 

 rotating water wheels, which make two hundred and fifty revolu- 

 tions per minute. In order to obtain direct driving that is, with- 

 out the intervention of toothed or friction gearing, or belt or rope 

 driving the revolving portions of the generator are arranged to 

 rotate in a horizontal instead of, as is usual, a vertical plane. 



A dynamo of any type whatever consists, as is well known, 

 essentially of two portions, one of which possesses motion with 

 respect to the other, viz., the armature and the field magnets. 

 Since the field magnets are almost invariably much heavier and 

 much less compact than the armature, the latter is usually chosen 

 as the moving part. In the case under discussion the contrary 

 has been decided on, the armature being fixed and the field mag- 

 nets rotating. This gives certain advantages in the matter of 

 less complicated electrical connections and of dispensing with the 

 armature's rubbing collectors altogether ; it also gives the advan- 

 tage much more important in this case than with smaller ma- 

 chines that, since the revolving magnets are arranged on a ring 

 and point inward, the attraction between them and the armature 

 core tends toward neutralization of the strains of centrifugal 

 force. The greatest advantage, however, attained by this method, 

 and again one which is of far greater value in the present case 

 than in ordinary practice, is the high degree of insulation possible 

 with fixed armature coils and connections. The requirements that 

 had to be met in the way of limiting the centrifugal strains were 

 that the product of the sum of the weights of the revolving parts 

 in pounds and the square of their velocities in feet per second 

 should not exceed eleven hundred million. The weight of the 

 moving parts of each dynamo was also limited to eighty thousand 

 pounds, while the weight of the turbine and its shaft amounts to 

 seventy-two thousand pounds. 



This whole weight of seventy-six tons acts in one vertical line 

 i. e., that of the turbine shaft and revolves two hundred and fifty 

 times per minute. It would have been very difficult to construct 

 thrust bearings to take up the whole of this strain, and a hydraulic 

 balancing piston has been resorted to for supporting it. This 

 device is simply a circular piston fast on the vertical turbine 

 shaft, set in a vertical cylinder. The supporting force consists of 



