Figure 67. — Gramme's magneto as provided 

 with Jamin's compound magnets. From 

 H. Fontaine, Eclairage a I'electricite, Paris, 

 1877, p. 104. 



6-disk Alliance machine. The voltage was equal to 

 that of 105 normal Bunsen cells, and the current was 

 equal to that of 5 such cells. Roughly speaking, such 

 power implied an efficiency of 50 percent. The cost 

 of the machine was £400 in England. Arc-light 

 demonstrations were made in the new Clock Tower 

 of Parliament in London in 1873, but since the 

 machine was quite apt to overheat the arc lights were 

 discontinued in favor of gas.^* 



At the beginning of 1874, Gramme cut down the 

 size and considerably increased the efficiency of both 

 the high-resistance and low-resistance generators by 

 relying completely on the principle of self-excitation.'" 

 The new model, called the type d^ atelier (figs. 65, 66), 

 reduced the number of armatures to one and reduced 



''^ Engineering, 1873, vol. 15, pp. 291-292. 



" Z. T. Gramme, "Sur les Nouveaux Perfectionnements 

 apportes aux machines magneto-electriques," Comptes rendus, 

 1874, vol. 79, pp. 1178-1182; ,\lfred N. Breguet, "Machine 

 magneto-elecfrique de M. Gramme," Revue industrielle, 1874, 

 vol. 3, pp. 405-410; Engineering, 1874, vol. 18, pp. 412-414. 



the number of electromagnets necessary to supply the 

 field. The electromagnets were still cylindrical in 

 form but were placed horizontally, with one above 

 the other, as in the original Ladd generator. The 

 axis of the single armature was horizontal and in 

 the same vertical plane as the electromagnets instead 

 of being perpendicular as in the Ladd machine. As 

 before, the magnetic circuit was completed by cast-iron 

 plates at the ends. Other changes made it possible 

 to increase the speed of rotation without excessive 

 heating of the armature. 



One electrochemical model and two arc-light models 

 were now produced. The electrochemical machine 

 (fig. 65) weighed 177.5 kg., measured 0.55 meters 

 square by 0.60 meters high, and used only 47 kg. of 

 copper wire for both armature and field. When driv- 

 en by a /3-hp. motor at 500 r.p.m. it would produce 

 the same amount of current as its predecessor. Two 

 sizes of the arc-light machine were made — a large 

 one based on the previous vertical arrangement of the 

 electromagnets (fig. 64) and a small one based on the 

 new horizontal arrangement of the type cTatelier (fig. 

 66). The large arc-light machine used six electro- 



PAPER 30: DEVELOPMENT OF ELECTRICAL TECHNOLOGY IN THE 19TH CENTURY: III 



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