Schilling telegraph

Lore & Background

Schilling's telegraph was demonstrated in St. Petersburg in 1832 using six wires for signalling, one wire for calling, and a common return, making eight wires in all. Each signal wire was connected to one of six needle instruments which together displayed a binary code. The calling wire had the same function as the ringing signal on a telephone, but was connected to a seventh needle. The code was read from the position of paper discs suspended on threads, coloured white on one side and black on the other. Each disc was turned by electromagnetic action on a magnetised needle. The sending equipment evolved from manually touching wires to battery poles to a more sophisticated arrangement: a piano-like keyboard with alternating white and black keys. There were sixteen keys altogether, each white and black pair of keys operating one of the wires. Positive or negative voltage was applied to the wire depending on whether the white or black key was pressed, causing the needle to swing in the opposite direction and show the corresponding side of the disc. The calling needle was similar to the signal needles but had additional mechanical apparatus: a horizontal arm that, when turned, pushed over a lever with a lead weight, releasing the detent of a clockwork alarm. In specifying a separate calling line and mechanism, Schilling followed the arrangements on the electrochemical telegraph of Samuel Thomas von Sömmerring, whose work Schilling became familiar with while a diplomat in Munich.

Reader's Guide

The Schilling telegraph is notable as an early electromagnetic telegraph that employed binary coding, using six needles to generate sufficient codepoints for the Russian alphabet. The ability to choose between displaying white or black discs doubled the codespace, though not all codepoints were used; those spanning the fewest keys were preferentially used. For the Latin alphabet, five needles were sufficient. The telegraph was developed to the stage where a project was initiated by the government to install it in Russia, but the idea was abandoned after Schilling died. Telegraphy in Russia subsequently used more advanced designs. The system's use of a separate calling line and alarm mechanism anticipated later telephone ringing signals. The keyboard sending arrangement, with metal bridges dipping into mercury reservoirs, allowed the operator to select polarity by pressing white or black keys, though only one set of keys (all white or all black) could be used at any one time.

Did You Know?

• The Schilling telegraph used six needle instruments to display a binary code for letters and numerals.
• The calling needle had a horizontal arm that released a clockwork alarm when a call was made.
• The sending keyboard had sixteen keys, with white and black pairs operating each signal wire.