(The). An alphabet used in telegraphic messages, invented by Professor Samuel F. B. Morse, of Massachusetts. The right-hand deflection of the electric needle corresponds to a dash, and the left-hand to a dot; and by means of dashes and dots every word may be spelt at length. Military signalling is performed in England by short and long flashes of a flag or some other instrument; the short flash corresponds with the dot, and the long with the dash. The following ten varieties will show how these two symbols are capable of endless combinations, $$$ etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894