A system was needed to signal to an engine house at Camden Town to start hauling the carriages back up the incline to the waiting locomotive.
As at Liverpool, the electric telegraph was in the end rejected in favour of a pneumatic system with whistles.
In later systems the letter board was dispensed with, and the code was read directly from the movement of the needles.
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The receiver consisted of a number of needles which could be moved by electromagnetic coils to point to letters on a board.
This feature was liked by early users who were unwilling to learn codes, and employers who did not want to invest in staff training.
The telegraph arose from a collaboration between William Fothergill Cooke and Charles Wheatstone, best known to schoolchildren from the eponymous Wheatstone bridge.
This was not a happy collaboration due to the differing objectives of the two men.
In May 1837 Cooke and Wheatstone patented a telegraph system which used a number of needles on a board that could be moved to point to letters of the alphabet.