Provide a piece of square card or pasteboard, and draw a circle on it, which circle is to be divided into 27 equal parts, in each of which parts must be written one of the capital letters of the alphabet, and the &, as in the figure. Let the centre of this circle be blank. Then draw another circle, also divided into 27 equal parts, in each of which write one of the small letters of the alphabet, and the &. This circle must be cut round, and made exactly to fit the blank space in the centre of the large circle, and must run round a pivot or pin. The person with whom you correspond must have a similar dial, and at the beginning of your letter you must put the capital letter, and at the end the small letter, which answer to each other when you have fixed your dial.
Suppose what you wish to communicate is as follows:
I am so watched I cannot see you as I promised; but I will meet you to-morrow in the park, with the letters, &c.
You begin with the letter T, and end with the letter m, which shows how you have fixed the dial, and how your correspondent must fix his, that he may decipher your letter.
Then, for I am, you write b uf, and so of the rest, as follows.
T b uf lh pumrvayx b rvugghm lyy rhn ul b ikhfblyx vnm b pbee fyym rhn mh-fhkkhp bg may iukd pbma may eymmykl, tw. m.
Another Way.
Take two pieces of card, pasteboard, or stiff paper, through which you cut long squares at different distances. One of these you keep yourself, and the other you give to your correspondent. You lay the pasteboard on a paper, and, in the spaces cut out, write what you would have understood by him only; then fill the intermediate spaces with any words that will connect the whole together, and make a different sense. When he receives it, he lays his pasteboard over the whole, and those words which are between crotchets [ ] form the intelligence you wish to communicate. For example: suppose you want to express these word,
"Don't trust Robert: I have found him a villain."