Now in order to provide a practical telegraph system permitting the interconnection of apparatus throughout the world, the first basic requisite is a standard signaling code; this code, moreover, must be of such nature as to use the simplest form of electrical signaling (such as make and break signals, or positive and negative signals), and the code should be of equal length for all characters.
The permutation code, where combinations of five plus and minus pulses will give thirty-two selective positions, was suggested as far back as 1833 by Gauss and Weber. Whitehouse, in 1854, and Barnett, in 1860, experimented further, using the permutation code to operate a recording mechanism. However, no practical means for actually printing letters and figures was found until 1882 when Jean Maurice Emile Baudot designed a multiplex system to permit the transmission of four messages in each direction over a single line circuit. Later, Baudot designed a tape printer in which the selecting and printing mechanisms comprised an ingenious arrangement of cooperating parts, including a rotating typewheel associated with a coded combiner wheel and five stationary elements selectively movable to received code positions, each element having an extending finger to be brought into contact with the periphery of the coded combiner wheel upon the completion of a selective code setting. When the code combination of the set fingers matched a code on the wheel, a print roller was released to press the recording tape against the typewheel and print the selected letter.
Although the Baudot Multiplex was used extensively in Europe, engineers and inventors in the United States had not produced a practical 5-unit permutation-code teleprinter system. They were constantly searching for a unit code system requiring a minimum number of electrical impulses to operate a telegraph printer. Various types of relay systems using distinctive signal pulses were proposed. A three-unit-code system that showed promise, and did not require synchronism, used four different electrical pulse conditions: a high voltage positive or negative pulse, and a low voltage positive or negative pulse. Records show that many inventors played with this code and that John Burry, C. L. Krum, G. A. Cardwell, and J. C. Barclay, among others, built operable equipment using such a code arrangement. The following excerpt from Cardwell’s patent No. 905,497 of December 1, 1908, may be of interest. It describes the code arrangement of four different line conditions in three signal groups to produce 36 different code combinations.
In order to energize the controller magnets in proper sequence to position the type wheel for printing a desired letter, a predetermined code or system of sending in the impulses is essential. In an instrument constructed by me in accordance with the present invention I have used the following:
1-2-1 letter space 1-2-3 carriage return 1-2-4 line space 1-3-1 type wheel shift 1-3-2 type wheel release 1-3-4 A 1-4-1 I 1-4-2 O 1-4-3 D 2-1-2 E 2-1-3 H 2-1-4 N 2-3-1 W 2-3-2 R 2-3-4 S 2-4-1 T 2-4-2 V 2-4-3 U 3-1-2 - 3-1-3 , 3-1-4 ? 3-2-1 Y 3-2-3 C 3-2-4 F 3-4-1 G 3-4-2 Q 3-4-3 L 4-1-2 M 4-1-3 J 4-1-4 B 4-2-1 X 4-2-3 Z 4-2-4 . 4-3-1 K 4-3-2 P 4-3-4 The numerals in the above code or system indicate the sequence of the impulses through the relay contacts 1, 2, 3 and 4.
| 1-2-1 | letter space |
| 1-2-3 | carriage return |
| 1-2-4 | line space |
| 1-3-1 | type wheel shift |
| 1-3-2 | type wheel release |
| 1-3-4 | A |
| 1-4-1 | I |
| 1-4-2 | O |
| 1-4-3 | D |
| 2-1-2 | E |
| 2-1-3 | H |
| 2-1-4 | N |
| 2-3-1 | W |
| 2-3-2 | R |
| 2-3-4 | S |
| 2-4-1 | T |
| 2-4-2 | V |
| 2-4-3 | U |
| 3-1-2 | - |
| 3-1-3 | , |
| 3-1-4 | ? |
| 3-2-1 | Y |
| 3-2-3 | C |
| 3-2-4 | F |
| 3-4-1 | G |
| 3-4-2 | Q |
| 3-4-3 | L |
| 4-1-2 | M |
| 4-1-3 | J |
| 4-1-4 | B |
| 4-2-1 | X |
| 4-2-3 | Z |
| 4-2-4 | . |
| 4-3-1 | K |
| 4-3-2 | P |
| 4-3-4 |
Cardwell’s backers formed the American Telegraph Typewriter Company and sold shares, claiming a great profitable future for their apparatus. A few printers were built, but, on extended service tests, the high-low-voltage feature proved to be impractical and the company folded.
J. C. Barclay of the Western Union Telegraph Company designed printing apparatus and perforated tape transmitting equipment for this type of system, but, after limited use of the high-low-voltage principle, he changed this feature to long and short pulses with discriminating relays. With later improvements, this system was put into service on a number of Western Union message circuits.
Note: Today, in the 1960s, the techniques of frequency division and electronics could be used for transmitting three different line conditions from a group of four different frequencies. In such a system, synchronism between send and receive terminals, or the start-stop method to control correct timing, is not needed. The transmission of any selected group of three, when received in succession at a teleprinter, will cause printing of a letter when the third receiving relay completes a circuit to the selected printing magnet. Transistor circuits with associated control elements could replace the relays.
Telegraph companies in the United States were mostly using the Morse and increased its efficiency through development of quadruplex operation and high-speed transmission systems. However, the quest for a more efficient printing telegraph system persisted and various types were proposed and tried. All made use of codes that were impractical for intercommunicating systems and, while some were used in message service by the telegraph companies, they did not appear to have any great advantage over the Morse telegraph.
In 1911, Western Union began investigating systems used in Europe. The first to be tested was the Creed, a system for transmitting and printing Continental or Morse code signals at high speed. After observing several other systems, the Murray Multiplex, an improved and modernized version of the Baudot Multiplex, was found to show better operating features and, due to the use of the five-unit permutation code, more efficient use of telegraph lines.