Secret Correspondence

To carry on a correspondence without the possibility of the meaning of
the letter being detected, in case it should be opened by any other
person, has employed the ingenuity of many. No method will be found
more effectual for this purpose, or more easy, than the following.

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.

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