Samuel Morse invented the telegraph and the simple signals transmitted across it, which were represented as dots and dashes. These signals became known as Morse code, which represents the letters of the alphabet and numbers from zero to nine.
A telegraph operator sent a message by tapping the code onto a telegraph machine. The machine then changed the taps into electrical signals, sending them out over wires to receivers. These receivers changed the electrical signals into Morse code printed on a piece of paper tape. Before the telephone and radio, the telegraph was the most efficient means of long-distance communication.