Wheatstone Cryptograph

The Wheatstone Cryptograph was invented by Sir Charles Wheatstone around 1870. He introduced his latest invention at the 1867 Paris Exposition. The Cryptograph attracted considerable interest but flaws in its security were noted within a few years, and going by the few survivors, it was probably not a commercial success. The small stylus in this example is missing. The face of the device is signed "The Cryptograph". C. Wheatstone, Inv'r.

The Wheatstone clock cryptograph, depicted here, was invented in the 1850s but was found to have a prior inventor, namely,  Decius Wadsworth, who invented it in 1817. The other device bearing Wheatstone's name is the Wheatstone bridge, which also had a prior inventor. Ironically, Wheatstone had an original cipher invention which was stronger than the Cryptograph, but allowed it to be named for his friend and neighbor, Lord Playfair.

The outer wheel of the Cryptograph has 27 characters (A-Z plus blank) while the inner wheel has 26 characters. For every revolution of the large hand, pointing to the 27 characters in the outer wheel, the small hand rotates one revolution plus one character. 
Both rings are made of solid, thick cardboard.
Rear view of the device. Note the small size of the gear housing, which is about the size of a US quarter. The device  diameter is exactly 3 7/8 inches while the thickness is 9/32 inch, not counting the hands.
Velvet lined case. The blue ribbon is used to lift the device from the carrying case. There is also a small loop at the upper left corner to hold the toothpick tool which is missing in this example. 
Leather case exterior
All photos  in this table via E-bay 
Principal parts of the Wheatstone Cryptogtaph. The large upper gear has 27 teeth and the lower gear has 26 teeth. Both gears intermesh with the small gear so that the large, lower gear goes around one revolution plus one character (27 total characters) for every revolution of the upper gear. The upper gear is fixed to the axle, which is also attached to the large hand. The lower gear has an inner protrusion that attaches to the small hand.
Closeup of the gear train. The gears make the Cryptograph easy to use and eliminated the need and vulnerability of a repeating key word. Too bad it isn't a stronger cipher.
Three small spikes that protrude about 1/16 inch on the bottom are used to hold the device firmly onto a wooden desk or any other "soft" surface. 
In the case. 
All photos and copy in this table by Ralph Simpson

Contributors and Credits:

2)  Ralph Simpson  <ralphenator(at)gmail.com>

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Nov 30/18