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The SingleNeedle Telegraph what is it
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An introduction to the single-needle telegraph. • William Lynd, author of ‘The Practical Telegraphist’, described the single-needle telegraph as ‘merely a vertical galvanometer’. It is a galvanometer, and it uses one magnetic needle to visually communicate over a great distance. Because it has only one needle, we can call it a binary system – the needle can only go left and right. As a result, the single-needle telegraph uses a code to communicate individual letters. Our telegraph, here, is using Morse Code. • So that we can understand, let’s have a look at its history. In eighteen twenty, Hans Christian Oersted, a Danish chemist and physicist, discovered that a magnetic field could be generated using electricity. In the same year, the galvanometer was invented by Johann Schweigger, a German physicist and chemist. The galvanometer lent itself to ‘distant writing’ and it wasn’t long before it was being developed as a means of communication. • The five-needle telegraph was developed by William Fothergill Cooke and Charles Wheatstone in the eighteen-thirties for a recent innovation – the railway – even then spreading across Great Britain. This five-needle telegraph puts five galvanometers on a diamond grid pattern to spell out individual words. Cooke and Wheatstone later introduced a double-needle telegraph in order to cut down on the number of electrical wires needed to make the telegraph work. • This was superseded in the eighteen-forty-three with the single needle telegraph, using – you won’t be surprised to hear – a single galvanometer to move a single needle. The system works using electro-magnetism. A magnetised needle is placed in the centre of a coil of wire. The coil is electrified with an electric current, creating an electro-magnetic field. The magnetised needle in this field reacts to it re-orientating itself at right angles to the wire. By arranging the coils and the needle in a particular manner, the needle is deflected to left or right, according to the direction of the electrical current passing through the wire. In order to send any message using only one needle, some form of code had to be developed. This was the single needle alphabet code. Here, though, instead of using the single needle alphabet code, we can see our telegraph using Morse code. • Many single-needle telegraphs have survived to the present day. This one dates from eighteen forty-four and was developed for the General Post Office. As you can see, it uses a handle rather than a key. The single needle telegraph superseded by a phalanx of new technologies, including the ABC telegraph, and was eventually eclipsed . . . by acoustic telegraphy. • #telegraphy #electromagnetism #galvanometer #Wheatstone
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