November 1887: The writing telegraph

An early forerunner of email — or perhaps that emblematically defunct piece of office equipment, the fax machine — the ‘writing telegraph’ was invented as a response to a perceived problem with telephones: the lack of a written record of a conversation. The device worked by encoding the movement of a stylus at the trasmitting station into electrical pulses and sending these pulses via the telegraph cable to the receiving station, where an arrangement of magnets forces a similar stylus to perform the same movements. Both styluses were in fact pens, writing onto a paper tape which moved underneath them at a steady speed — so a written message at one end would be reproduced perfectly at the other.

The inner workings of this device were in fact rather ingenious. The transmitter pen’s movements were transmitted via mechanical linkages (via a float sitting in a cup of viscous glycerine, to damp out any jerkiness of the user’s hands) to two series of thin carbon discs set at right-angles to each other and housed in a hard rubber, and placed ‘in circuit’ with the telegraph wire itself. Moving the stylus caused ‘pressure points’ to press on the series of discs, which reduced the electrical resistance in the circuit by an amount proportional to how far the stylus had been moved.