102 ELECTRIC LIGHTING. 



tically, having in its centre a rotating electro-magnetic system 

 composed of as many magnetic cores as there are electro- 

 magnets on the crown. Fig. 33 shows this machine, in which 

 the rotating interior electro-magnets represent the inducing, 

 and the fixed electro-magnets the induced system. 



The inducing system, which is merely the magnetic pinion 

 of Lon tin's generators already described on page 98, is com- 

 posed of an iron cylinder to which are riveted a series of iron 

 plates somewhat resembling the teeth of a pinion, and on 

 these the magnetizing coils A A are wound for tension. In 

 order that the spires of the coils may not shift under the 

 influence of the centrifugal force, and of the elongation 

 caused by the rather large amount of heat developed, the 

 plates of iron forming the cores are thicker at their free 

 extremities than at their points of connection with the iron 

 cylinder, and this greater thickness plays the part of retain- 

 ing discs for the spires, which are further maintained in their 

 position by abutting against horizontal iron pieces mounted 

 on two bronze wheels. Finally, the coils are so wound that 

 the polarity of the cores are reversed from one plate to the 

 other, so that the motion of the drum brings magnets of 

 alternately opposite poles before the iron cores of the induced 

 system, which thus receive alternately reversed polarizations. 



This inducing system is of course magnetized continuously 

 by the dynamo-electric generator, which we have already 

 described, and which may be mounted on the same axle. 

 Another machine may, however, be substituted for this 

 generator; or even a voltaic battery may be used, but in 

 that case the conditions will be very disadvantageous as 

 regards economy. 



The induced system is composed, as we have seen, of a 

 large stationary iron ring, fitted inside with a series of iron 

 plates fixed transversely, like the teeth of a wheel projecting 

 internally, and surrounded with magnetizing coils, B B B. 

 These coils are connected to each other in couples, so as to 

 form a complete electro-magnetic system, and their free ex- 



