2.9: Detail - Morse Code

Samuel F. B. Morse (1791–1872) was a landscape and portrait painter from Charleston, MA. He frequently travelled from his studio in New York City to work with clients across the nation. He was in Washington, DC in 1825 when his wife Lucretia died suddenly of heart failure. Morse learned of this event as rapidly as was possible at the time, through a letter sent from New York to Washington, but it was too late for him to return in time for her funeral.

As a painter Morse met with only moderate success. Although his paintings can be found today in major museums—the Museum of Fine Arts, Boston, has seven—he never had an important impact on contemporary art. It was as an inventor that he is best known. (He combined his interest in technology and his passion for art in an interesting way: in 1839 he learned the French technique of making daguerreotypes and for a few years supported himself by teaching it to others.)

Returning from Europe in 1832, he happened to meet a fellow passenger who had visited the great European physics laboratories. He learned about the experiments of Ampère, Franklin, and others wherein electricity passed instantaneously over any known length of wire. Morse realized this meant that intelligence could be transmitted instantaneously by electricity. He understood from the circumstances of his wife’s death the need for rapid communication. Before his ship even arrived in New York he invented the first version of what is today called Morse Code. His later inventions included the hand key and some receiving devices. It was in 1844 that he sent his famous message WHAT HATH GOD WROUGHT from Washington to Baltimore. That event caught the public fancy, and produced national excitement not unlike the Internet euphoria 150 years later.

Morse Code consists of a sequence of short and long pulses or tones (dots and dashes) separated by short periods of silence. A person generates Morse Code by making and breaking an electrical connection on a hand key, and the person on the other end of the line listens to the sequence of dots and dashes and converts them to letters, spaces, and punctuation. The modern form of Morse Code is shown in Table 2.8. The at sign was added in 2004 to accommodate email addresses. Two of the dozen or so control codes are shown. Non-English letters and some of the less used punctuation marks are omitted.

Table 2.8: Morse Code

A	• –	K	– • –	U	• • –	0	– – – – –	Question mark	• • – – • •
B	– • • •	L	• – • •	V	• • • –	1	• – – – –	Apostrophe	• – – – – •
C	– • – •	M	– –	W	• – –	2	• • – – –	Parenthesis	– • – – • –
D	– • •	N	– •	X	– • • –	3	• • • – –	Quotation mark	• – • • – •
E	•	O	– – –	Y	– • – –	4	• • • • –	Fraction bar	– • • – •
F	• • – •	P	• – – •	Z	– – • •	5	• • • • •	Equals	– • • • –
G	– – •	Q	– – • –	Period	• – • – • –	6	– • • • •	Slash	– • • – •
H	• • • •	R	• – •	Comma	– – • • – –	7	– – • • •	At sign	• – – • – •
I	• •	S	• • •	Hyphen	– • • • • –	8	– – – • •	Delete prior word	• • • • • • • •
J	• – – –	T	–	Colon	– – – • • •	9	– – – – •	End of Transmission	• – • – •

If the duration of a dot is taken to be one unit of time then that of a dash is three units. The space between the dots and dashes within one character is one unit, that between characters is three units, and that between words seven units. Space is not considered a character, as it is in ASCII.

Unlike ASCII, Morse Code is a variable-length code. Morse realized that some letters in the English alphabet are more frequently used than others, and gave them shorter codes. Thus messages could be transmitted faster on average, than if all letters were equally long. Table 2.9 shows the frequency of the letters in written English (the number of times each letter is, on average, found per 1000 letters).

Morse Code was well designed for use on telegraphs, and it later saw use in radio communications before AM radios could carry voice. Until 1999 it was a required mode of communication for ocean vessels, even though it was rarely used (the theory apparently was that some older craft might not have converted to more modern communications gear). Ability to send and receive Morse Code is still a requirement for U.S. citizens who want some types of amateur radio license.

Table 2.9: Relative frequency of letters in written English

132	E	61	S	24	U
104	T	53	H	20	G, P, Y
82	A	38	D	19	W
80	O	34	L	14	B
71	N	29	F	9	V
68	R	27	C	4	K
63	I	25	M	1	X, J, Q, Z

Since Morse Code is designed to be heard, not seen, Table 2.8 is only marginally useful. You cannot learn Morse Code from looking at the dots and dashes on paper; you have to hear them. If you want to listen to it on text of your choice, try a synthesizer on the Internet, such as

• http://morsecode.scphillips.com/jtranslator.html

A comparison of Tables 2.8 and 2.9 reveals that Morse did a fairly good job of assigning short sequences to the more common letters. It is reported that he did this not by counting letters in books and newspapers, but by visiting a print shop. The printing presses at the time used movable type, with separate letters assembled by humans into lines. Each letter was available in multiple copies for each font and size, in the form of pieces of lead. Morse simply counted the pieces of type available for each letter of the alphabet, assuming that the printers knew their business and stocked their cases with the right quantity of each letter. The wooden type cases were arranged with two rows, the capital letters in the upper one and small letters in the lower one. Printers referred to those from the upper row of the case as “uppercase” letters.