VARIOUS GENERATORS OF ELECTRIC LIGHT. 81 



press the two springs of the collector, which are formed by 

 a sort of brush of metallic wires held by supports, as may 

 be observed on the right of the ring in Fig. 19. These 

 plates are, of course, separated by layers of ebonite in order 

 to insulate them electrically. In the figure the inducing 

 electro-magnets are placed horizontally at the top and 

 bottom of the machine, and their polar expansions are seen 

 in the metallic pieces surrounding the ring, serving at the 

 same time as supports to the stems of the rubbing pieces 

 and to the binding screws of the induced circuit. 



Gramme machines of the last pattern are little more than 

 65 centimetres long, 41 centimetres wide, and 50 centi- 

 metres high ; they weigh 1 75 kilogrammes, and with 2\ horse- 

 power, giving a speed of revolution of 850 turns per minute, 

 they yield an electric light equal to 2,500 candles or 270 

 Carcel lamps. 



We shall presently see that Gramme has constructed another 

 system of machines to supply currents alternately reversed, 

 and so arranged that the action of the machine may be 

 divided and made to yield currents in several distinct circuits. 

 This arrangement enabled the illumination of the Avenue de 

 r Opera by JablochkofT candles to be carried out. 



We shall not speak of other forms of the Gramme machine 

 except in the chapter on the applications of the electric 

 light. All the necessary details as regards these may, how- 

 ever, be found in Fontaine's work, entitled L'Eclairage a 

 r electricite. 



Schuckert has somewhat modified the Gramme machine 

 by employing a flat ring, and by utilizing the magnetism of 

 the electro-magnets on the laternal faces of the ring, instead 

 of on the cylindrical part; but we are not sure that the 

 alleged increase of power which has been attributed to this 

 arrangement is real, and the machine appears to us merely 

 a copy of the French invention. 



We may say the same of a machine constructed by RapiefT, 

 in which the ring is so arranged to be subjected to induction 



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