Double-needle magneto-electric telegraph instrument patented in 1848 and manufactured by Messrs Henley and Forster in England. The case is missing, revealing the mechanism

The complete instrument had a large square dial on the sloping top of a wooden case, with two needles pivoted side by side on the dial. Pressing either of two levers, one on each side of the case, rotated a coil between the poles of a magnet and generated a pulse of electric current which was transmitted along the telegraph line to the receiving indstrument. There the pulse caused a deflection of one of the needles on the dial. The pattern of needle deflections indicated to the operator which letter of the alphabet was being received.

This instrument is an example of a double-needle telegraph system which did not require any source of electrical power such as a battery. The system was not widely used but was in operation on the Adelaide-Semaphore line in South Australia in the 1850s before being superseded by morse instruments.

Physical Description

Mechanism of instrument. Normally housed in wooden case with sloping top surrounding a square dial. Two needles mounted side by side on dial. Dial marked with letters of the alphabet and corresponding needle deflection sequences. Two levers with paddle handles, normally projecting from front of case, below front edge of sloping top. One lever on each side of instrument. Levers connected to coils which rotate between magnets. All mounted on wooden base.

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