'Cryptograph' circular coding machine

"The Cryptograph" : a circular coding machine, 3 7/8" diameter, invented by C. Wheatstone; in wood box

Wheatstone invented the cryptograph to secure privacy for messages sent by the electric telegraph.

The long arm of the instrument is turned to the letter in the clear message and the short arm indicates the letter to be put in the coded message. The two arms are connected by gear wheels. Agreed rules as to initial position and direction of rotation of the arms and arrangement of the letters are followed, so that a similar machine can be used for decoding.