The siphon recorder, patented by William Thomson in 1867, was the principal receiver on long cables for some 50 years. When new receivers came along, they used the same basic mechanism: threads connected to a sensitive moving coil.
| Current from the cable passed through a small coil between the arms of a powerful magnet. Silk threads attach the coil to a glass tube. One end of the tube sits in a reservoir of ink; the other hovers over a moving strip of paper. A pulse of current causes the coil to twist; the threads move the tube; and the tube deposits ink on the paper, moving to the right for dot, to the left for dash. |
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Siphon recorder, 1870s National Museum of American History, from Western Union | |
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A relay receives a faint signal and automatically sends it on its way with a stronger electric pulse. Here, threads from the coil attach to a metal feeler that then makes contact with one of two conducting strips on a rotating "drum." Contact generates a fresh signal. |
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Brown drum relay, 1915 National Museum of American History, from Western Union | |
| In this relay, threads from the coil move two wire resistors that are part of a circuit called a "Wheatstone bridge." Small tubes blow air on the wires to cool them, but as the resistors move, one is cooled more (decreasing resistance) and the other is cooled less (increasing resistance). This causes the "bridge" to send out a strong, new pulse of current. |
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Heurtley magnifier, about 1910 National Museum of American History, from Western Union | |
The job required a lot of hard labor. The technique was the same worldwide and had not changed since the 1860s.
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Fao, Iraq, on the Persian Gulf, 1865 Courtesy of the Library of Congress |
Sennen Cove, Penzance, England, 1910 National Museum of American History, from The Science Museum, London |
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Rio de Janeiro, Brazil, 1925 National Museum of American History, from The Science Museum, London |
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A concern with profits and losses made cable companies cautious. Sir James Anderson, Statistics of Telegraphy (London, 1872) Smithsonian Institution Libraries |
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This compendium of good telegraph practice at the turn of the century reveals that technology and technique had changed little in 50 years. The author was the son of the chief engineer who oversaw the laying of the first Atlantic cable. |
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Charles Bright, Submarine Telegraphs: Their History, Construction, and Working (London, 1898) Smithsonian Institution Libraries | |
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Cable was made by extruding gutta percha around a copper-wire core, then wrapping it all with iron wires. This technology remained virtually unchanged for more than 100 years. Some of these machines (still in use in 1973) dated from 1914, and were essentially the same as the wire machines of the 1860s.
Listen to sounds from this factory, 1973 |
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Machine for wrapping iron armor on cable, Greenwich, England, 1973 Courtesy of The Science Museum, London | |
