124 LOCALIZED ELECTRIZATION. 



wheels are so arranged that their respective teeth only correspond 

 by half their surfaces, so that the two springs 9 and 15 only rest 

 at once upon the metallic parts of the teeth for one half of their 

 extent. 



Things being thus arranged, let us first follow the course of a 

 battery current tlirough the commutator C (fig. 40) and to the 

 extremities of the wire of the primary coil of a double-induction 

 volta-electric apparatus, represented by the knobs 7 and 11. The 

 two poles, n, p, of the pile are brought to 1 and 2, knobs which 

 communicate with each of the isolated halves, 3 and 4, of the 

 commutator C, so that they can be made to change sides by 

 turning the button D of tlie commutator from left to right, or vice 

 versa. One of these poles — suppose the negative — passes from 3 

 and 5 to 6, a knob to which is attached a conductor in communi- 

 cation with 7, one of the extremities of the wire of the primary 

 coil ; the other, or positive pole, p, goes from 2 and 4 to 8, a 

 metallic support communicating with the metallic teeth of the 

 wheel A. At 9 is a spring in contact with these metallic teeth, 

 and connected with 10, a knob to which is attached a conductor 

 in communication with 11, the other extremity of the wire of 

 the primary coil. 



In these conditions the wheel A is only an ordinary rheotome, 

 producing by each of its teeth, or at each intermission, while a 

 rotatory motion is communicated to it, two currents in opposite 

 directions, one at tlie completion and the other at the interruption 

 of the circuit, in the wire of the second coil, the extremities of 

 which, represented by 12 and 13, are connected by some metallic 

 or organic conductor. 



But if one of the extremities of this wire — 13, for example, — 

 is conducted by a M'ire to 14, and so to 15, a spring resting on the 

 metallic teeth of tlie wheel B, which themselves communicate 

 with 16, the support of this wheel, and with the knob 17, it is 

 manifest that if the circuit of the second coil is completed by a 

 conductor placed in communication with the knob 17, and Avith 

 the knob 12, which represent the two extremities of the wire of 

 the second coil, the organ placed in the circuit will receive only 

 the current of interruption, when the wheel is turned from left to 

 right, and only the current of completion when the wheel is 

 turned from right to left. The connection between the metallic 

 teeth and the wood of the wheels A and B will explain how an 

 organ placed in the circuit will receive at pleasure only the one 

 current or the other. 



In fact, the circuit of the second coil being completed, by the 

 contact of the spring 15 with the metal teeth of the wheel B, only 



