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Western Electric Pole-Changer Relay |
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This is a beautiful and elaborate telegraph relay built by Western Electric in the 1880's. This device is a "clock -face gravity-battery pole-changer", as used by the Western Union Telegraph Company, according to a 1901 telegraphy book. A pole changer provided a means by which the polarity of a battery inserted into a telegraph circuit could be reversed without breaking the circuit. The polarity of the battery connection was determined by whether or not the relay coils were energized. The contacts were located in a protective enclosure with a glass front which resembled a clock. The "gravity-battery" was a commonly used form of wet-cell battery. This type of cell used a copper anode, zinc cathode, in solutions of copper sulfate and zinc sulfate. The cell relied on the differing specific gravities of the two solutions to keep them separated, hence the term "gravity-battery". A pole changer was an integral part of a "double-current" or polar telegraph system, particularly, a duplex or quadruplex system in which two or four messages could be sent over a single wire circuit simultaneously. This design (minus the glass front housing) was patented on March 3, 1888 (US patent no. 379,062). The application was filed in 1886. |
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