English: Illustration of railroad track circuit invented by Dr. William Robinson in 1872, from his circular of January 1874. Legend:
C-Primary signal. E-Magnet. H-Line wire circuit. I-Track battery. K-Primary signal battery. L-Distant signal. R-Relay.
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{{Information |Description={{en|1=Illustration of railroad track circuit invented by Dr. William Robinson in 1872, from his circular of January 1874. Legend:<br /> C-Primary signal. E-Magnet. H-Line wire circuit. I-Track battery. K-Pri
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