When the numbering has been finished, or while you are making the numbering, notice what letters and how many must be written, or put on paper.  For it is not the case that you proceed here by the process given in the aforementioned Chapter 5 – the process, namely, whereby, to express O coming after O, you write the letter X this being, as you see, the twentieth letter in the order of the tabular alphabet, -- but you must proceed by a different method.  Four you must write, in order to express the above-mentioned numbers, with three numerical letters only, I.V.X.  The letter L, or the letter C, which letters are also used in combinations to express certain numbers, you must always use, whenever you have finished a number, as a dividing mark for the other letters, that no confusion may arise and the reader be left in ignorance what letters are joined or must be joined together;  whereby it will result that the text given above will be written secretly thus: XXCXXCXXCXXCXVIIICVIIICXIIICXVCVIILVIIC
VICVLXIIIICXVIICXIIICVIIICXICVCVIIICXIICVIIIC.

Since, however, one may easily suspect, from those numerical letters, that the matter depends on a system of numbering, the process will be more elegant, as well as safer, if you cut off entirely from the one when you wish to remain in ignorance of the secret all interest in the matter.  This may be done by substituting for these numerical letters, I, V, X and C, or L, the letters FGH and Q, respectively, and then forming the writing from these letters.  The process will take place thus: O is the twentieth letter after O: you must write for it, therefore, HH. M is the twentieth letter after M: write once more, after the mark of separation, Q, HH, M is again the twentieth letter after M: write still again HH.  I is the twentieth letter after I: again write HH.  V is the eighteenth letter after A: write, therefore, HGFFF.  M is the eighth letter after C: write, therefore GFFF.  And so continue, always placing by the side of the other letters the mark of division Q.  For the sake of an example let the form be written: HhqhhqhhqhhqhgfffQgfffqfffqhfffqhgqgffqgffqgfqhqhffffqhgfffqhffffqgfffqhfqgqgfffqhffqgfffqq.

This is the method of writing.  The reader, knowing the key, must count in order from the letters of the key, until, beneath the number represented in the table by the said letters, he find the letter of the secret.

In the same way proceed with reference to the device of Oblique Transposition, according to the second table in Chapter 14: substitute in the table numerical letters.  Or you may also follow the first table (or, if you prefer, any other table), writing horizontally the seven numerical letters, I, V, X, L,C,D,M, and laterally the first three of these, I, V, X, and then proceeding by various methods.  See, also, the tables presented in cc 16 and 18 of the following Book.  In the same way, you will have a method of using this Mediate Transposition, if you look through the two tables given in Chapter Nineteen of the following Book, and apply the device of this Mediate Interchange.