Ch. 18.         263

in the present case, the exterior alphabet, the horizontal as well as the perpendicular one, must be written.  In the preceding cases, it appeared only as an accident, as was explained in the last line.

In resolving the sentence of the secret into the various groups of two letters, the same process may and should be observed that I have indicated above, c.16, in the paragraph beginning “ The praxis learn as follows, etc.

Finally, the union of the two letters of the middle alphabet being made in the same way as before, the angle of union is disclosed, and, with it, the Transpositive letter.  And, also, regard being at the same time had for the exterior capital alphabet, which is, as it were, dedicated for alternate use as a key, what may be called the key-letter Appears.  For example, in transposing the aforementioned secret, Cras expectabis adventum meum, the letters Cr first come up for Transposition.  The former being taken from the horizontal, and the latter from the perpendicular, middle alphabet, there is shown the letter L, and , at the same time, from the perpendicular line of letters for the exterior alphabet, the letter C, or from the horizontal line, the letter M.  this exterior letter must be written by the side of the other letter, differently, however, from before, in this respect, that, unless otherwise agreed upon, the horizontal exterior letter is to be placed first, with the letter which belongs to the secret following (e.g. ML), while, vice versa, the perpendicular exterior letter is to be placed after the letter of the secret (as, in the same example, LC).  One may also, however, so arrange the letters that all the letters belonging to the secret are placed first, with the key-letters following in proper order.  A number of further variations of the arrangement are also possible.