According as one pole of the
battery or the other was applied to the line by means of the key, the
current deflected the needle to one side or the other. There were five
separate circuits actuating five different needles. The latter were
pivoted in rows across the middle of a dial shaped like a diamond, and
having the letters of the alphabet arranged upon it in such a way that a
letter was literally pointed out by the current deflecting two of the
needles towards it.
An experimental line, with a sixth return wire, was run between the
Euston terminus and Camden Town station of the London and North Western
Railway on July 25, 1837. The actual distance was only one and a half
mile, but spare wire had been inserted in the circuit to increase its
length. It was late in the evening before the trial took place. Mr.
Cooke was in charge at Camden Town, while Mr. Robert Stephenson and
other gentlemen looked on; and Wheatstone sat at his instrument in a
dingy little room, lit by a tallow candle, near the booking-office at
Euston. Wheatstone sent the first message, to which Cooke replied, and
'never,' said Wheatstone, 'did I feel such a tumultuous sensation
before, as when, all alone in the still room, I heard the needles click,
and as I spelled the words, I felt all the magnitude of the invention
pronounced to be practicable beyond cavil or dispute.
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