ABSTRACT
The memorable discovery of electro-magnetism by Ersted in 1819 was soon followed by attempts to apply it to the production of signals at a distance. Ampere first pointed out the possibility of making an electric telegraph with needles surrounded by wires; but he proposed to have a separate needle and wire for each signal to be transmitted. The spread of telegraph lines, and the extent to which this mode of communication is used by the public, may be illustrated by a few particulars regarding the Central Telegraphic Office in London. The Bell telephone is used by speaking distinctly before the mouthpiece of the transmitter, while the listener at the other end of the line applies the mouth-piece of his instrument to his ear, and one wire is sufficient with good earth connections, although sometimes a second wire is employed to complete the circuit.
