Reflections: 75 years ago

Multiplex Telegraphy. “I had constructed two ordinary direct current motors of the simplest form, an ordinary two pole field and single coil armature conveniently arranged for use as either direct or alternating current machines. The armature circuits were connected at one end to an ordinary two-part commutator and at the other to two insulated ring contacts. They are shown by a simple diagram in Fig. 1, where both are connected in a single circuit. The armature of the machine M
¹
was normally open at the ring contacts, and could be closed either by connecting the ring or through an external circuit. Such a circuit was made to include the field coils of the machine M
²
, and the armature of this machine was connected in the direct current circuit from the poles of the battery. Thus connected, the two machines moved as one; the machine M
²
following all the fluctuations of speed in the machine M
¹
, as if their armatures were carried by the same spindle, the speed being varied between wide limits.”