Wheatstone system

Lore & Background

The Wheatstone system was an automated telegraph system that replaced a human operator with machines capable of sending and recording Morse code at a consistent fast rate. The system included a perforator, which prepared punched paper tape called a Wheatstone slip, a transmitter that read the tape and converted the symbols into dots and dashes encoded as mark and space electric currents on the telegraph line, and a receiver at the other end of the telegraph line that printed the Morse symbols. The system was invented by Charles Wheatstone. Enhancements could be made so that it was a duplex system, able to send and receive on the same line simultaneously.

The Wheatstone slip was a paper tape that contained holes in a pattern to control the mark and space signals on the telegraph line. The paper tape was from 0.46 to 0.48 inches in width, (but the standard width is from 0.472 to 0.475 inches) and a standard thickness of 0.004 to 0.0045 inches. Olive oil coating lubricated the punch process. There were three rows of holes. The middle row forms a rack so that a star wheel can move the paper forward. Every used position on the tape has a middle hole punched. The top hole indicates when to turn on the mark signal on the line, and the bottom hole says to turn off the mark signal. Each vertical column represents a time interval in the Morse code, including the spacing between the holes. The holes are spaced 0.1 inches apart. A column of three holes turns on the mark at the beginning of the interval, and turns it off at the end making a dot. If there is a top hole without a bottom, and then the next column has a bottom without a top hole, mark is on for three intervals, and a dash is represented. If there is only a centre hole, then nothing changes, and this would normally be used to put in space between letters and words.

The Wheatstone perforator was a development of Alexander Bain's 1848 manually operated hole punch machine for his 'fast telegraph'. It produced Wheatstone slips using three buttons (or keys) labelled 'A', 'A1' and 'A2'. 'A' punched the pattern for dot, 'A1' punched the pattern for space, and 'A2' punched the dash pattern in two columns. The keys were so difficult to press that fist-held rubber-tipped mallets were used to depress them and operate the punches. Using this, invalid combinations of holes could not be produced. The blank paper tape was fed in from the right over a roller and came out the left side. It was oriented in a vertical plane. The paper punches were labelled with numbers: 1 for the top hole of the dot, 2 for the sprocket hole for dot, and 3 for the bottom hole for dot. When a dash was punched, extra hole punches to the right punched a centre hole with number 4 and a bottom hole with number 5. The perforator was introduced in 1867. It enabled transmission speeds on a telegraph line to increase to 70 words per minute. The very first message ever punched onto a tape was 'SOS EIOS'. The manual perforator was subsequently replaced by keyboard perforators like the Gell keyboard perforator or Kleinschmidt keyboard perforator.

Reader's Guide

The Wheatstone system represented a significant advancement in telegraphy by automating the process of sending and receiving Morse code, increasing transmission speeds to 70 words per minute. Its use of punched paper tape (the Wheatstone slip) allowed for consistent, high-speed signaling that was not possible with a human operator. The system's duplex capability, enabling simultaneous sending and receiving on the same line, further enhanced its efficiency. The perforator, introduced in 1867, was a development of Alexander Bain's earlier machine and required the use of mallets to operate its stiff keys. The transmitter and receiver worked together to convert the punched patterns into electrical signals and then back into printed Morse code on a paper strip. The resulting telegrams were strips of paper tape with the Morse code printed on it, pasted onto a form, and later retyped for the final message. The system's legacy includes its influence on later keyboard perforators, such as the Gell and Kleinschmidt models, and its role in demonstrating the potential for automated telegraph communication.

Did You Know?

• The Wheatstone system could be enhanced to operate as a duplex system, sending and receiving on the same line simultaneously.
• The very first message ever punched onto a Wheatstone slip was 'SOS EIOS'.
• The Wheatstone receiver's electromagnet had two windings of 100 ohms each, which could be connected in parallel or series for 50 or 200 ohm resistance.