Chapter V
On Fortuitous Simple Transposition.

I have set forth Natural and Arbitrary Transposition.  We come now to Fortuitous Transposition.  Here the Transpositive letters are collected, not in accordance with their natural alphabetic order, or at the will of one who makes an order, but fortuitously, by means of numbers, under the subsidiary direction of a fixed fundamental, or principle, which, following Porta, Bk.2.c.2, I call by special application, a key; though Porta, in the above passage, is speaking of a subdivision only, and does not touch on the general class.  See above, Bk.2.c.8, where I have said that not only words, but also letters, alphabets, points, and virgules are used as keys; as, for example, in the present case, a single letter.  This much I have thought it necessary to promise.  Now with regard to the method itself of hiding the secret, this depends on an alphabetic arrangement, which I will make by explaining the following table.  An acquaintance with the Mode will be gained from an inspection of the table itself and an understanding of its structure and of the method of using the key; wherefore I put here at the head of what I have to say the table which I have taken from de Vigenere, p.230.

There is no need that I should linger over the explanation of the table.  The method of interchanging the letters depends on what is called therein  number,  as being that which directs all.  What the nature of this directing principle is, will be learned better from its application.

The method of use, or the application, is shown thus:  First, we must select a secret text, at our pleasure, for example, let it be the following: Omnium rerum vicissitudo.  Next we must consider the key, or fixed principle of counting, and this may, in this Mode, be taken in a variety of ways.  It may be taken, for instance, from the first letter of the secret, by the retention of this letter, or it may be taken from some other letter selected from another part of the alphabet.

If the first letter of the secret is used as key, we proceed thus:  First, this initial letter is allowed to stand without Transposition and is put on paper in its proper form.  From this point we may again proceed in two ways, on the basis of a twofold method of counting.  First, in accordance with the directions of the following rule: whatever the number of  places each letter of the secret stands removed from the immediately preceding letter, the letter of the tabular alphabet having in the table such number written beneath it must be taken.