A needle telegraph is an electrical telegraph that uses indicating needles moved electromagnetically as its means of displaying messages. It is one of the two main types of electromagnetic telegraph, the other being the armature system, as exemplified by the telegraph of Samuel Morse in the United States. Needle telegraphs were widely used in Europe and the British Empire during the nineteenth century. Needle telegraphs were suggested shortly after Hans Christian Ørsted discovered that electric currents could deflect compass needles in 1820. Pavel Schilling developed a telegraph using needles suspended by threads. This was intended for installation in Russia for government use, but Schilling died in 1837 before it could be implemented. In 1833 Carl Friedrich Gauss and Wilhelm Eduard Weber in Göttingen built a telegraph line that was used for scientific study and communication between university sites. In 1837 Carl August von Steinheil adapted Gauss and Weber's rather cumbersome apparatus for use on various German railways. In England, William Fothergill Cooke started building telegraphs, initially based on Schilling's design. With Charles Wheatstone, Cooke produced a much improved design. This was taken up by several railway companies. Cooke's Electric Telegraph Company, formed in 1846, provided the first public telegraph service. The needle telegraphs of the Electric Telegraph Company and their rivals were the standard form of telegraphy for the better part of the nineteenth century in the United Kingdom. They continued in use even after the Morse telegraph became the official standard in the UK in 1870. Some were still in use well in to the twentieth century.
Early ideas
The history of the needle telegraph began with the landmark discovery, published by Hans Christian Ørsted on 21 April 1820, that an electric current deflected the needle of a nearby compass. Almost immediately, other scholars realised the potential this phenomenon had for building an electric telegraph. The first to suggest this was French mathematician Pierre-Simon Laplace. On 2 October, André-Marie Ampère, acting on Laplace's suggestion, sent a paper on this idea to the Paris Academy of Sciences. Ampère's (theoretical) telegraph had a pair of wires for each letter of the alphabet with a keyboard to control which pair was connected to a battery. At the receiving end, Ampère placed small magnets (needles) under the wires. The effect on the magnet in Ampère's scheme would have been very weak because he did not form the wire into a coil around the needle to multiply the magnetic effect of the current. Johann Schweigger had already invented the galvanometer (in September) using such a multiplier, but Ampère either had not yet got the news, or failed to realise its significance for a telegraph. Peter Barlow investigated Ampère's idea, but thought it would not work. In 1824 he published his results, saying that the effect on the compass was seriously diminished "with only 200 feet of wire". Barlow, and other eminent academics of the time who agreed with him, were criticised by some writers for retarding the development of the telegraph. A decade passed between Ampère's paper being read and the first electromagnetic telegraphs being built.
Development
Schilling telegraph
It was not until 1829 that the idea of applying Schweigger style multipliers to telegraph needles was mooted by Gustav Theodor Fechner in Leipzig. Fechner, in other respects following the scheme of Ampère, also suggested a pair of wires for each letter (twenty-four in the German alphabet) laid underground to connect Leipzig with Dresden. Fechner's idea was taken up by William Ritchie of the Royal Institution of Great Britain in 1830. Ritchie used twenty-six pairs of wires run across a lecture room as a demonstration of principle. Meanwhile, Pavel Schilling in Russia constructed a series of telegraphs also using Schweigger multipliers. The exact date that Schilling switched from developing electrochemical telegraphs to needle telegraphs is not known, but Hamel says he showed one in early development to Tsar Alexander I who died in 1825. In 1832, Schilling developed the first needle telegraph (and the first electromagnetic telegraph of any kind) intended for practical use. Tsar Nicholas I initiated a project to connect St. Petersburg with Kronstadt using Schilling's telegraph, but it was cancelled on Schilling's death in 1837. Schilling's scheme had some drawbacks. Although it used far fewer wires than proposed by Ampère or used by Ritchie, his 1832 demonstration still used eight wires, which made the system expensive to install over very long distances. Schilling's scheme used a bank of six needle instruments which between them displayed a binary code representing a letter of the alphabet. Schilling did devise a code that allowed the letter code to be sent serially to a single needle instrument, but he found that the dignitaries he demonstrated the telegraph to could understand the six-needle version more readily. Transmission speed was very slow on the multi-needle telegraph, perhaps as low as four characters per minute, and even slower on the single-needle version. The reason for this was principally that Schilling had severely overdamped the movement of the needles by slowing them with a platinum paddle in a cup of mercury. Schilling's method of mounting the needle by suspending it by a silk thread over the multiplier also had practical difficulties. The instrument had to be carefully levelled before use and could not be moved or disturbed while in use.
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