52 



SCIENCE. 



[Vol. XIV. No. 338 



The shaft bearings, bearing standards, base plate, and armature- 

 slides are cast in one piece. The shaft carries two heavy cast-iron 

 yoke-pieces 27 inches in diameter. To each of these are screwed, 

 at equal radial and circumferential distances, the wrought-iron 

 cores of 12 magnets of alternating polarity. Thus the whole ro- 

 tating mass acts as a fly-wheel, tending to neutralize any variation 

 in the speed of the prime generator. As the nominal speed of the 

 machine is less than 1,100 revolutions per minute, the structural 

 strength is more than sufficient to meet all demands made by cen - 

 trifugal force. Further than this, the mechanical stress is less 

 when the magnets are excited than when the alternator is running 

 without load, as the lines of magnetic force between the faces of 

 opposing poles tend to counteract centrifugal force. In machines 



silver frame consisting of two semicircles bolted together on the line 

 of the vertical diameter. Into the slots of the frame slip the six 

 mounted armature-coils, the tongue on the edge of the one en- 

 gaging with the groove on the edge of the next. The coils thus 

 thrust into the intense inagnetic field constitute a disk nine-six- 

 teenths of an inch in thickness, and with an opening in the centre 

 through which passes the revolving shaft. As there is no magnetic 

 metal in the armature, there are no local currents to waste the en- 

 ergy. 



The several coils are insulated carefully ; and the stationary 

 armature, as a whole, is insulated from the bed-plate on which it 

 rests. The coils are joined in series, the binding-posts adjacent to 

 any radial line of division between the two coik constituting fixed 





FIGS, i, 0, AND 8. -BRUSH ALTERNATING SYSTE.M. 



FIG. 8. 



of larger size, as usual, the speed is less, that of the 150,000- watt 

 dynamo being not more than 700 revolutions per minute. 



The most interesting part of the alternator is the fixed armature, 

 shown in Fig. 2. The vertical disk is occupied by flat armature- 

 coils made of insulated copper ribbon wound on porcelain cores. 

 The copper ribbon of each coil is re-enforced on either side with 

 strong insulating material of the same thickness as the porcelain. 

 One of these re-enforcements is grooved, and the other tongued. 

 The coil, consisting thus of core, ribbon, and re-enforcements, has 

 an angular width of 60 degrees. The upper part of each face of 

 each coil is covered with an insulating plate five-sixteenths of an 

 inch thick. The coil thus built up and insulated is set in German- 

 silver holders, cut from turned rings, and held together by sunk- 

 headed screws. Each terminal of the copper ribbon connects with 

 a binding-post, as shown. 



The six armature-coils thus mounted are carried in a German- 



terminals for the main line. There is no commutator, and there 

 are no collecting brushes to take the alternating current from the 

 rotating parts. 



The low resistance of the armature-coils is evident. It would 

 seem impossible for one of them to burn out. None ever has 

 burned out ; but if one should, it may be removed, and a new one 

 readily put in its place, in three minutes, or the injured coil may be 

 shunted out of the circuit and the dynamo kept running with the 

 other five until the time for shutting down. The coil section com- 

 plete weighs only about 20 pounds. The whole armature may be 

 removed by loosening the coupling-bolts, and sliding each half of 

 the frame from between the field-magnets (Fig. 3). 



In action, the 24 field-magnets of the alternator are excited by 

 the direct current from a Brush dynamo of the well-known form. 

 This exciting current is carried to the brushes that rest upon the 

 two uncut insulating rings (shown at the left of Fig. i), and thence 



