Morse code is a method of sending text messages by keying in a series of electronic pulses, usually represented as a short pulse (called a "dot") and a long pulse (a "dash"). The code was devised by Samuel F. B. Morse in the 1840s to work with his invention of the telegraph, the first invention to effectively exploit electromagnetism for long-distance communication. The early telegrapher, often one who was at a railroad station interconnected with others along miles of telegraph pole lines, would tap a key up and down to send a succession of characters that the receiving telegrapher could read from tape (later operators learned to read the transmissions simply by listening). In the original version, the key down separated by a pause (key up) from the next letter was a dot (or, as it sounded to the telegrapher, a "dit") and the key down quickly twice in succession was a dash (a "dah" or "dit-dit"). Each text character was represented by a dot, dash, or some combination.
In the late 1800s, as new keying technology became prevalent, a somewhat different representation of dots and dashes was used for certain letters in what became known as the International Morse Code or Continental Code. American Morse code, however, continued to be used in the U.S. into the 1960s.
There are various stories concerning how the Morse code was originally developed. According to one account, Samuel Morse went to a printer's shop and counted the amount of printer type the printer had for each letter of the alphabet. He then interpreted these counts as approximations of the relative frequency of each letter in typical English text. He organized the Morse code so that the shortest symbols were associated with the most frequent characters. Thus, for example, E and T, the most often-used letters in the English language, were represented by a single dot and single dash, respectively. The least frequently occurring letters, such as J and Y, and numerals and punctuation marks were given longer and more complex representations. No differentiation was made for uppercase and lowercase.
Morse code offers a slow but reliable means of transmitting and receiving wireless text messages through conditions involving noise, fading, or interference. This is primarily because its simple binary code (key down or key up) allows for an extremely narrow bandwidth. In addition, the human ear and brain make a remarkably good digital receiving device. Nowadays, Morse code is used to a limited extent by amateur radio operators, landline telegraphers, and military radio operators.