Page "Telegraphy" Paragraph 18

Carl Friedrich Gauss and Wilhelm Weber built and first used for regular communication the electromagnetic telegraph in 1833 in Göttingen, connecting Göttingen Observatory and the Institute of Physics, covering a distance of about 1 km.

The setup consisted of a coil which could be moved up and down over the end of two magnetic steel bars.

The resulting induction current was transmitted through two wires to the receiver, consisting of a galvanometer.

The direction of the current could be reversed by commuting the two wires in a special switch.

Therefore, Gauss and Weber chose to encode the alphabet in a binary code, using positive current and negative as the two states.