in the resistance of the circuit (abcdefghik), and thus affect the intensity of the current traversing it.

But the magnetization of (i) - an electro-magnet palced in the circuit - is dependent upon the intensity of the current traversing its coils. Hence the vibrations of M cause the electro- magnet (i) to attract its armature, S with varying force.

If the armature S be so arranged as to be capable