Earth-return telegraph

Lore & Background

The first use of an earth return to complete an electric circuit was by William Watson in 1747, excluding experiments using a water return path. Watson sent an electric current through 2,800 feet of iron wire with an earth-return path, later increasing that distance to two miles. These early experiments were not aimed at producing a telegraph but rather designed to determine the speed of electricity. Watson's result seems to have been unknown or forgotten by early telegraph experimenters who used a return conductor. One early exception was a telegraph invented by Harrison Gray Dyar in 1826 using friction machines, demonstrated around a race course on Long Island, New York, in 1828 using an earth-return circuit.

The first telegraph put into service with an earth return is due to Carl August von Steinheil in 1838. Steinheil was working on providing a telegraph along the Nuremberg–Fürth railway line. He first attempted, at the suggestion of Carl Friedrich Gauss, to use the two rails of the track as telegraph conductors. This failed because the rails were not well insulated from earth, but this initial failure made Steinheil realise that the earth could be used as a conductor, and he then succeeded with only one wire and an earth return. Steinheil declined to patent the idea, wishing to make it freely available as a public service.

The introduction of electric power, especially electric tram lines in the 1880s, seriously disturbed earth-return telegraph lines. The starting and stopping of the trams generated large electromagnetic spikes which overwhelmed code pulses on telegraph lines. This was particularly a problem on lines where high-speed automatic working was in use and, most especially, on submarine telegraph cables. At the same time, the rise of telephony, which was even more intolerant to the interference on earth-return systems, started to displace electrical telegraphy altogether, bringing to an end the earth-return technique in telecommunications.

Reader's Guide

Earth-return telegraph significantly reduced the cost of long-distance telegraphy by eliminating one of the two metal wires normally required for a complete circuit. This saving was substantial on lines that might run for hundreds or even thousands of miles. The advantage was not so apparent in early multiwire systems such as Pavel Schilling's experimental system of 1832 with six signal wires, or the Cooke and Wheatstone five-needle telegraph of 1837, which did not require a return conductor at all. However, the expense of multiwire systems rapidly led to single-signal-wire systems becoming the norm, making the cost of the return wire much more significant and leading to earth return becoming standard.

The earth-return technique faced serious problems towards the end of the 19th century due to electric trams, which generated interference that overwhelmed code pulses. Some circuits were returned to the old metal-conductor return system. The rise of telephony, even more intolerant to the interference on earth-return systems, eventually displaced electrical telegraphy altogether. The technique thus had a period of dominance in the mid-to-late 19th century but was ultimately superseded by other technologies. Its legacy lies in demonstrating that the earth itself could serve as a practical conductor, a principle that influenced later developments in electrical engineering.

Did You Know?

• The first earth-return telegraph put into service was by Carl August von Steinheil in 1838 on the Nuremberg–Fürth railway line.
• William Watson demonstrated earth return in 1747 by sending an electric current through 2,800 feet of iron wire.
• Steinheil declined to patent the earth-return idea, making it freely available as a public service.
• Electric trams in the 1880s seriously disturbed earth-return telegraph lines with electromagnetic spikes.

Pioneering Experiments and the Search for Electrical Communication

The dream of sending messages through electricity at a distance stretches back further than most realize. In 1753, an anonymous contributor to the Scots Magazine—signed C.M. and posted from Renfrew, possibly Charles Marshall—proposed an electrostatic telegraph that would use one wire per letter, with pith balls at the far end registering deflections. Georges-Louis Le Sage built a working model in 1774, though it spanned only two rooms of his home and required a separate wire for each of the 26 alphabet letters. A crucial turning point came in 1800 when Alessandro Volta introduced his voltaic pile, offering a continuous low-voltage current that far surpassed the brief discharges of electrostatic machines and Leyden jars. In 1809, German physician Samuel Thomas von Sömmering created an electrochemical telegraph based on an 1804 design by Spanish polymath Francisco Salva Campillo. Their apparatus employed up to 35 wires, each dipped in a glass tube of acid; sequential currents electrolysed the acid, releasing hydrogen bubbles beside the corresponding letter for the operator to read. These early efforts, while impractical, laid the groundwork for everything that followed.

Two Rival Families of Telegraph Machines

Once electrical telegraphy moved from laboratory curiosity to practical use, two fundamentally different approaches dominated the field. The first family, known as needle telegraphs, relied on electromagnetic force: a current traveling down a wire would swing a needle-shaped pointer over a printed list, effectively pointing to a specific letter or symbol. Early models in this category required multiple needles and therefore multiple wires between stations. The Cooke and Wheatstone telegraph, invented in 1837, became the first commercial needle system and the most widely deployed of its kind. The second family, the armature systems, took a different tack. Here the current activated a telegraph sounder that produced an audible click, and operators communicated by sending those clicks in coded rhythmic patterns. Samuel Morse's system, devised in 1838, became the archetype of this approach. By 1865, the Morse system had been adopted as the international standard for telegraphic communication, employing a modified version of Morse's original code that had been refined for use on German railways.

Railway Signalling and the Democratization of Messaging

The telegraph's earliest and most consequential industrial application came from the railway world. Emerging railway companies adopted electrical telegraphy to provide signals for train control systems, minimizing the chances of trains colliding with one another. This was organized around the signalling block system, in which signal boxes positioned along a line communicated with neighboring boxes using telegraphic single-stroke bells and three-position needle telegraph instruments. Beyond the rails, the technology transformed public communication. In the 1840s, electrical telegraphy supplanted older optical systems such as semaphores and became the standard method for dispatching urgent messages. By the latter half of the nineteenth century, most developed nations had built out commercial telegraph networks, with local telegraph offices in most cities and towns. For a fee, any member of the public could compose a telegram addressed to virtually any person in the country, making near-instant written communication accessible far beyond governments and businesses.

Global Cables, Wireless Successors, and a Slow Fade

The telegraph's reach expanded from national networks to a truly global scale beginning in 1850, when submarine cables first enabled rapid communication between people on different continents. This near-instant transmission of messages across and between continents carried widespread social and economic impacts that reshaped how the world operated. The technology also served as a direct precursor to the next great leap in communication: Guglielmo Marconi's invention of wireless telegraphy, the first means of radiowave telecommunication, which he began developing in 1894. Yet the wired telegraph's dominance was already eroding. In the early twentieth century, manual operation of telegraph machines gave way to teleprinter networks, and the growing use of the telephone confined telegraphy to a handful of specialist applications. For the general public, sending a telegram dwindled to a novelty reserved for special occasions such as greetings. Finally, the rise of the Internet and email during the 1990s rendered dedicated telegraphy networks largely obsolete, closing a chapter that had spanned more than a century of human communication.