Telegraph, four-needle telegraph

Telegraphic instruments were developed for use on London's new railway network. Telegraph wires ran alongside railway tracks to transmit messages, signals and, time. Before the 1830s, national time was not standardised with each area of Britain having its own ‘local’ time, based on the sunrise and sunset. To operate the newly built railways safely and to a timetable, railway companies used the telegraph system to introduce a national standard 'railway' time system. By 1855, this had been brought in line with Greenwich Mean time, telegraphed along cables the length and breadth of Britain.
William Fothergill Cooke and Charles Wheatstone patented the world’s first practical commercial electric telegraph system in 1837. Demonstrations using multi-needle instruments were given to the Directors of the London and Birmingham Railway (L&BR) at Euston and Camden Town later in 1837 but the electric telegraph was not adopted by the L&BR at this time. In 1839 Cooke installed a demonstration line alongside the Great Western Railway (GWR) between London Paddington and West Drayton using four-needle instruments.
This four-needle telegraph's patent (No. 7614) was used at intermediate stations to send or receive messages in both directions. Telegraphs like these included a change-over switch or 'circuit director'. The four-needle telegraph also represented a transitional stage between the five-needle instrument, where each letter could be directly indicated, and the later double-needle instrument, which employed a signalling code.
The use of telegraphy by the railway companies prompted wider interest from other businesses and the government.