of the establishment of Mutual Interchange.  The two-letter groups assigned to the squares may be so changed that, for AL, is written, or put down, in the table LA:  for BT, is written TB;  for GS, SG;  and so the process of variation continues.  There also lurk elsewhere in the table a number of mysteries and variations, which I leave to the clever reader to discover.  The table is encircled, both at the top and at the side, by a capital alphabet, and within by numbers.  The horizontal capital alphabet is written in eleven squares (indicated by Roman numerals written beneath), two letters in each square, notwithstanding which fact, one Transpositive letter in the interior table may be taken for two letters of the secret, though each of these squares also contains two letters.  Each letter of the perpendicular capitals occupies a square by itself, which is designated by a number written at the side in small figures.  For the rest, the process of Transposition is, as I have said, the same in this as in the preceding Mode;  the words of the secret are resolved in the same way, two letters being always joined, for Transposition, whether this takes place in a single sentence or in two sentences combined, as shown in Chapter 16.  The writing also has nothing peculiar, except that, after the letter, the key-number is added, as will appear from the subjoined example.  This I will give immediately, after having first spoken of the reason why, in Transposition, we often thus join two sentences.  The reason is that sometimes, by solving the one sentence and keeping the more secret sentence hidden, we can satisfy some person who is perchance pressing us to disclose the secret sense.  Now as an example let us take this sentence, which we wish to put in hidden writing: Cras expectabis adventu nostrum hora quinta matutina.  This sentence may be transposed by itself, in accordance with the instructions given in Chapter 16; but one may also, at his pleasure, add another sentence, which it is not essential to keep hidden: e.g. these proper names: Gustavus Selenus.  These two words, since the letters thereof when resolved do not equal in number the letters of the secret, must be repeated as many times as is necessary.  Whereby it will result that the following form of letters, with the key added, will appear:   B7L19a17f18g1t19Ml9g17b17O5a10e5e12f19al7u4
r19L5r122 a18r19O11x12O13g17n18g16n19O11m8 etc.   The reader will solve by first looking to the number in the perpendicular line, and then picking out the square in the horizontal line, or direction straight across, wherein the letter B is written.  When the letter B has been found, there first appears, straight across in the reverse direction, beyond the said key number, the perpendicular letter which was the second of the two letters requiring to be transposed.  Then, at the top, directly above, is the first letter which was to be transposed.  Thus, in the given example, we have the letter B with the key 7.  Directly across from the said number 7, in the second square, is found the letter B, which has at the side the capital letter G, and at the top the letter C.  Instead of numbers, one may also use the letters of the open expression, and, even if these be discovered by the clever investigator, the real secret will none the less remain hidden.  For one will naturally conclude, after having discovered a certain sense, that the letters which he sees interspersed and which belong to the more secret sense, are superfluous, being inserted from outside sources and without significance.