94 ELECTRIC LIGHTING. 



mutator A B. The opposite coils b d are, it will be seen, 

 joined end to end, but these connections are shown in the 

 figure for only one pair of coils. In order to place the com- 

 mutator in a good position, the ends of the wires are made 

 to pass through a hollow axle to reach the projecting parts. 



The commutator, A B, is put together in such a manner 

 that three pairs of coils are always in communication with 

 the circuit of the machine, and the remaining pair has its 

 circuit interrupted in the place of the neutral line of the 

 ring. 



The commutator itself is made of plates of copper, a e y 



fixed on rings of insulat- 

 ing matter and shaped 

 \\ as in ordinary apparatus 



of this kind. 



The Committee points 

 out that by reason of 

 the iron surfaces which 

 separate the coils being 

 exposed, the ring of this 

 machine is able the more 

 FIG. 30. readily to part with its 



heat, which seldom rises 



above 120 Fahrenheit, in spite of its very great velocity 

 of rotation. The machine is blamed, however, for its 

 rather loud noise, which is attributed to the resistance of 

 the air, but which is nothing but the sounds due to the alter- 

 nations of magnetization and demagnetization in the portions 

 of the ring. These effects are produced also in De Meritens' 

 and in Lontin's machines, and, what is still more curious, 

 the sounds are repeated by the Jablochkoff candles placed 

 in the circuit of these machines. This effect is connected 

 with the electro-telephonic transmissions, which are explained 

 in our work on the telephone. 



In another form of the machine there are two commu- 

 tators corresponding with the two systems formed of the odd 



