Alfred Vail developed a system in which each letter or symbol is sent individually, using combinations of dots, dashes, and pauses. With the agreement between the two, this system was known as the American Morse Code; used to transmit the first telegraph message.
The American Morse Code, sometimes referred to as "Railroad Morse" uses a slightly different structures of dots and dashes and uniquely spaces also to represent numbers, letters, and special characters. This style of Morse Code was developed for land operators working over telegraph wires rather than radio signals.
This style of code was developed to accommodate the way in which operators listened to Morse code sent to them. Rather than hearing tones from a speaker or headphones, this telegraph would hear two clicks from a mechanical sounding device for each key movement, unlike the Modern International Morse code. (A tribute to Morse Code)