File:Foucault's regulator.jpg

English: Foucault constructed in 1858 the apparatus shown in Fig. 426, taken from La Lumière Électrique. The two carbons a and b are arranged horizontally, fixed upon the rollers c c′. The two springs R R′ tend to move the carbons towards each other, and are connected by means of a string running over the pulley P with it, so that the motion can take place only when the clockwork M also moves. The lever L and the string P′ P′′ P′′′ are so arranged that c and c′ move at the same time, only c′, having the negative carbon, moves much more slowly than c. The electric current before it enters the carbons has to pass the electro-magnet E. To the armature A, which is movable about r, the rod D is fastened; and according to the position which the armature has, it will liberate or stop the clockwork. The spring r tends to lift the armature from the electro-magnet. By means of the catch d the clockwork may be stopped by the hand. The voltameter K compensates for variations in the strength of current ; increasing or diminishing the resistance by allowing the plates to take different positions in the fluid. When the carbons a and b are at the right distance from each other, the current will have its normal strength, and the electro-magnet attracts the armature A. In this position the rod D stops the clockwork, and the carbons remain stationary. If the distance of the carbons by means of their consumption becomes too large, i.e. increases the resistance in the circuit, the spring r overcomes the force of attraction of the magnet E, and the annature A is lifted off; the rod D no longer stops the clockwork, and c c′ can move towards each other until the resistance of the circuit has its original value, and the arc has its normal length. The current will then have its original strength, and cause the electro- magnet E to attract the armature A again.