Re: Telegraphone

Yup, telegraphones - when you're too cheap to put in a second wire. Phones usually use a balanced pair to transmit sound, but telegraphones were designed for use on the cheap - they used the telegraph wire for one side of the circuit, and the earth return for the other. Thus, they tended to have poor frequency response (the other party would sound muffled) and had a good deal of noise on the line from the earth return. The telegraph was pretty much unaffected, as the inductance of the large coils naturally filtered out the audio frequency signals.

The advantage is that you could hook on to the existing wire and transmit voice, so conductors could call up the DS if they ran into trouble without knowing Morse. The downside was that, at least by all accounts I've read, the voice quality varied between bad and unusable depending on weather and line condition.