sentences:  When the permanent magnet north is repelled, the switch closes to one pole, and when the permanent magnet south is repelled the switch closes to the other pole.To make it practical, Edison found some additional relays were necessary to provide hysteresis that prevented the switch from being in-determinant or fluttering at the moment of current reversals and to send the separated signal to the appropriate sound emitter.While this is conceptually elementary to modern engineers, one has to appreciate that multiplexing was a patent-worthy breakthrough and a huge economic win for telegraphy since most of the challenge and expense was in the long wires between stations.