Editing Telegraphy (section)

=== Railway telegraphy ===

[[File:GWR Cooke and Wheatstone double needle telegraph instrument.jpg|thumb|left|An early Cooke and Wheatstone double-needle railway telegraph instrument at the [[National Railway Museum]]]] 
[[File:Block instrument.jpg|thumb|right|A block signalling instrument as used in Britain in the 20th century]]

{{See also|Railway signalling}}
Railway signal telegraphy was developed in Britain from the 1840s onward. It was used to manage railway traffic and to prevent accidents as part of the railway signalling system. On 12 June 1837 Cooke and Wheatstone were awarded a patent for an electric telegraph.<ref>{{Citation |title= How the UK's railways shaped the development of the telegraph |publisher= British Telecom |url= http://home.bt.com/tech-gadgets/history-of-communication-uk-railways-telegraph-patent-cooke-wheatstone-11364186628315 }}</ref> This was demonstrated between [[Euston railway station]]—where Wheatstone was located—and the engine house at Camden Town—where Cooke was stationed, together with [[Robert Stephenson]], the [[London and Birmingham Railway]] line's chief engineer. The messages were for the operation of the rope-haulage system for pulling trains up the 1 in 77 bank. The world's first permanent railway telegraph was completed in July 1839 between London Paddington and West Drayton on the [[Great Western Railway]] with an electric telegraph using a four-needle system.

The concept of a [[Signalling block system|signalling "block" system]] was proposed by Cooke in 1842. Railway signal telegraphy did not change in essence from Cooke's initial concept for more than a century. In this system each line of railway was divided into sections or blocks of varying length. Entry to and exit from the block was to be authorised by electric telegraph and signalled by the line-side semaphore signals, so that only a single train could occupy the rails. In Cooke's original system, a single-needle telegraph was adapted to indicate just two messages: "Line Clear" and "Line Blocked". The [[Signalman (rail)|signaller]] would adjust his line-side signals accordingly. As first implemented in 1844 each station had as many needles as there were stations on the line, giving a complete picture of the traffic. As lines expanded, a sequence of pairs of single-needle instruments were adopted, one pair for each block in each direction.<ref>{{Citation |last= Roberts |first= Steven |author-link= Stephen Roberts (historian) |title= Distant Writing: 15. Railway Signal Telegraphy 1838 – 1868 |url= http://distantwriting.co.uk/railwaysignaltelegaphy.html }}</ref>
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