Editing Electrical telegraph (section)

===Telegraphic improvements===
[[File: Components of the electromechanical telegraph network. Proce Wellcome V0025510.jpg|thumb|left|Wheatstone automated telegraph network equipment]]
A continuing goal in telegraphy was to reduce the cost per message by reducing hand-work, or increasing the sending rate. There were many experiments with moving pointers, and various electrical encodings. However, most systems were too complicated and unreliable. A successful expedient to reduce the cost per message was the development of [[telegraphese]].

The first system that did not require skilled technicians to operate was Charles Wheatstone's ABC system in 1840 in which the letters of the alphabet were arranged around a clock-face, and the signal caused a needle to indicate the letter. This early system required the receiver to be present in real time to record the message and it reached speeds of up to 15 words a minute.

In 1846, [[Alexander Bain (inventor)|Alexander Bain]] patented a chemical telegraph in Edinburgh. The signal current moved an iron pen across a moving paper tape soaked in a mixture of ammonium nitrate and potassium ferrocyanide, decomposing the chemical and producing readable blue marks in Morse code. The speed of the printing telegraph was 16 and a half words per minute, but messages still required translation into English by live copyists. Chemical telegraphy came to an end in the US in 1851, when the Morse group defeated the Bain patent in the US District Court.<ref>{{cite book |last=Oslin |first=George P |title=The Story of Telecommunications |publisher=Mercer University Press |year=1992 |page=69 |isbn=9780865544185}}</ref>

For a brief period, starting with the New York–Boston line in 1848, some telegraph networks began to employ sound operators, who were trained to understand Morse code aurally. Gradually, the use of sound operators eliminated the need for telegraph receivers to include register and tape. Instead, the receiving instrument was developed into a "sounder", an electromagnet that was energized by a current and attracted a small iron lever. When the sounding key was opened or closed, the sounder lever struck an anvil. The Morse operator distinguished a dot and a dash by the short or long interval between the two clicks. The message was then written out in long-hand.<ref>{{cite book |last=Oslin |first=George P |title=The Story of Telecommunications |publisher=Mercer University Press |year=1992 |page=67 |isbn=9780865544185}}</ref>

[[Royal Earl House]] developed and patented a letter-printing telegraph system in 1846 which employed an alphabetic keyboard for the transmitter and automatically printed the letters on paper at the receiver,<ref>{{cite web |url=http://blog.gatunka.com/2014/04/14/letter-printing-telegraph-us-patent-4464/ |title=Royal Earl House Printing-Telegraph Patent #4464, 1846 |access-date=25 April 2014}}</ref> and followed this up with a steam-powered version in 1852.<ref>{{cite web |url=http://blog.gatunka.com/2014/04/15/steam-powered-letter-printing-telegraph-us-patent-9505/ |title=Royal Earl House Steam-Powered Printing-Telegraph Patent #9505, 1852 |access-date=25 April 2014}}</ref> Advocates of printing telegraphy said it would eliminate Morse operators' errors. The House machine was used on four main American telegraph lines by 1852. The speed of the House machine was announced as 2600 words an hour.<ref>{{cite book |last=Oslin |first=George P |title=The Story of Telecommunications |publisher=Mercer University Press |year=1992 |page=71 |isbn=9780865544185}}</ref>

[[File:Clavier Baudot.jpg|thumb|upright=1.5|A Baudot keyboard, 1884]]
[[David Edward Hughes]] invented the printing telegraph in 1855; it used a keyboard of 26 keys for the alphabet and a spinning type wheel that determined the letter being transmitted by the length of time that had elapsed since the previous transmission. The system allowed for automatic recording on the receiving end. The system was very stable and accurate and became accepted around the world.<ref>{{cite web |url=http://people.clarkson.edu/~ekatz/scientists/hughes.html |title=David Edward Hughes |access-date=29 September 2010 |date=14 April 2007 |publisher=Clarkson University |archive-url=https://web.archive.org/web/20080422072443/http://people.clarkson.edu/~ekatz/scientists/hughes.html |archive-date=22 April 2008}}</ref>

The next improvement was the [[Baudot code]] of 1874. French engineer [[Émile Baudot]] patented a printing telegraph in which the signals were translated automatically into typographic characters. Each character was assigned a five-bit code, mechanically interpreted from the state of five on/off switches. Operators had to maintain a steady rhythm, and the usual speed of operation was 30 words per minute.{{sfn|Beauchamp|2001|pp=394–395}}

By this point, reception had been automated, but the speed and accuracy of the transmission were still limited to the skill of the human operator. The first practical automated system was patented by Charles Wheatstone. The message (in [[Morse code]]) was typed onto a piece of perforated tape using a keyboard-like device called the 'Stick Punch'. The transmitter automatically ran the tape through and transmitted the message at the then exceptionally high speed of 70 words per minute.

====Teleprinters====
{{main|Teleprinter|Telex}}
{{more citations needed section|date=January 2020}}
[[File:Phelps' Electro-motor Printing Telegraph.jpg|thumb|Phelps' Electro-motor Printing Telegraph from {{circa|1880}}, the last and most advanced telegraphy mechanism designed by [[George May Phelps]]]]
[[File:Bundesarchiv Bild 183-2008-0516-500, Fernschreibmaschine mit Telefonanschluss.jpg|thumb|right|A Creed Model 7 teleprinter in 1930]]
[[File:Teletype-IMG 7289.jpg|right|thumb|upright=1|[[Teletype Model 33]] ASR (Automatic Send and Receive)]]
An early successful [[teleprinter]] was invented by [[Frederick G. Creed]]. In [[Glasgow]] he created his first keyboard perforator, which used compressed air to punch the holes. He also created a reperforator (receiving perforator) and a printer. The reperforator punched incoming Morse signals onto paper tape and the printer decoded this tape to produce alphanumeric characters on plain paper. This was the origin of the Creed High Speed Automatic Printing System, which could run at an unprecedented 200 words per minute. His system was adopted by the ''[[Daily Mail]]'' for daily transmission of the newspaper contents.

With the invention of the [[teletypewriter]], telegraphic encoding became fully automated. Early teletypewriters used the ITA-1 [[Baudot code]], a five-bit code. This yielded only thirty-two codes, so it was over-defined into two "shifts", "letters" and "figures". An explicit, unshared shift code prefaced each set of letters and figures. In 1901, Baudot's code was modified by [[Donald Murray (inventor)|Donald Murray]].

In the 1930s, teleprinters were produced by [[Teletype Corporation|Teletype]] in the US, [[Creed & Company|Creed]] in Britain and [[Siemens]] in Germany.

By 1935, message routing was the last great barrier to full automation. Large telegraphy providers began to develop systems that used [[telephone exchange|telephone-like rotary dialling]] to connect teletypewriters. These resulting systems were called "Telex" (TELegraph EXchange). Telex machines first performed rotary-telephone-style [[pulse dialling]] for [[circuit switching]], and then sent data by [[ITA2]]. This "type A" Telex routing functionally automated message routing.

The first wide-coverage Telex network was implemented in Germany during the 1930s<ref>{{Cite web |title=Telegraphy and Telex |url=https://new.siemens.com/global/en/company/about/history/technology/information-and-communications-technology/telegraphy-and-telex.html |url-status=live |access-date=25 March 2021 |archive-url=https://web.archive.org/web/20190726052037/https://new.siemens.com/global/en/company/about/history/technology/information-and-communications-technology/telegraphy-and-telex.html |archive-date=26 July 2019}}</ref> as a network used to communicate within the government.

At the rate of 45.45 (±0.5%) [[baud]] – considered speedy at the time – up to 25 telex channels could share a single long-distance telephone channel by using ''[[voice frequency telegraphy]] [[frequency-division multiplexing|multiplexing]]'', making telex the least expensive method of reliable long-distance communication.

Automatic teleprinter exchange service was introduced into Canada by [[CPR Telegraphs]] and [[CN Telegraph]] in July 1957 and in 1958, [[Western Union]] started to build a Telex network in the United States.<ref>Phillip R. Easterlin, "Telex in New York", Western Union Technical Review, April 1959: 45</ref>

====The harmonic telegraph====
{{main|Invention of the telephone}}
{{see also|Acoustic telegraphy}}
The most expensive aspect of a telegraph system was the installation – the laying of the wire, which was often very long. The costs would be better covered by finding a way to send more than one message at a time through the single wire, thus increasing revenue per wire. Early devices included the [[duplex (telegraph)|duplex]] and the [[Quadruplex telegraph|quadruplex]] which allowed, respectively, one or two telegraph transmissions in each direction. However, an even greater number of channels was desired on the busiest lines. In the latter half of the 1800s, several inventors worked towards creating a method for doing just that, including [[Charles Bourseul]], [[Thomas Edison]], [[Elisha Gray]], and [[Alexander Graham Bell]].

One approach was to have resonators of several different frequencies act as carriers of a modulated on-off signal. This was the harmonic telegraph, a form of [[Multiplexing#Frequency-division multiplexing|frequency-division multiplexing]]. These various frequencies, referred to as harmonics, could then be combined into one complex signal and sent down the single wire. On the receiving end, the frequencies would be separated with a matching set of resonators.

With a set of frequencies being carried down a single wire, it was realized that the human voice itself could be transmitted electrically through the wire. This effort led to the [[invention of the telephone]]. (While the work toward packing multiple telegraph signals onto one wire led to telephony, later advances would pack multiple voice signals onto one wire by increasing the bandwidth by modulating frequencies much higher than human hearing. Eventually, the bandwidth was widened much further by using laser light signals sent through fiber optic cables. Fiber optic transmission can carry 25,000 telephone signals simultaneously down a single fiber.<ref>{{Cite web |url=https://www.explainthatstuff.com/fiberoptics.html |title=How does fiber optics work? |date=11 June 2006}}</ref>)