I have read that, in the early days of the telegraph, two wires were used, but Steinheil, of optics fame, discovered that the circuit could be completed by 'earth return', using the ground as return ...conductor? That's my question. It's hard to believe that currents strong enough to operate the telegraph could be produced by low-voltage batteries, with the high presumable resistance of the earth... In those telegraph systems, or in some single-wire, earth-return power supplies that exist in some countries, does the electricity really circulate through the ground? Or does the ground work as a 'capacitor', as I have seen mentioned somewhere? But, if it's a capacitor, then where are the plates...?