APPENDIX. 



[The following Notes on some old treatises on the art of writing in cipher are re- 

 ferred to by Mr. Ellis, at p. 658. note 1. J. S.] 



THE earliest writer, I believe, on ciphers, except Trithemius whom 

 he quotes, is John Baptist Porta, whose work De occultis lite- 

 rarum notis was reprinted in Strasburg in 1606. The first edi- 

 tion was published when Porta was a young man. The species of 

 ciphers which Bacon mentions are described in this work. What he 

 calls the ciphra simplex is doubtless that in which each letter is re- 

 placed by another in accordance with a secret alphabet. (Porta, ii. 

 c. 5.) The manner of modifying this by introducing non-significants 

 and by other contrivances is described in the following chapter. 

 The wheel cipher is described in chapters 7, 8, 9. It is that in which 

 the ordinary alphabet and a secret one are written respectively on 

 the rim of two concentric disks, so that each letter of the first 

 corresponds in each position of the second (which is movable) to a 

 letter of the secret alphabet. Thus in each position of the movable 

 disk we have a distinct cipher, and in using the instrument this disk 

 is made to turn through a given angle after each letter has been 

 written. The ciphra clams is described by Porta, book ii. 15, 16. 

 It is a cipher of position ; that is, one in which the difficulty is ob- 

 tained not by replacing the ordinary alphabet by a new one, but by 

 deranging the order in which the letters of a sentence or paragraph 

 succeed each other. This is done according to a certain form of words 

 or series of numbers which constitute the key. The cipher of words 

 was given by Trithemius and in another form by Porta, ii. 19. (and 

 in a different shape, v. 16.). It is a cipher which is meant to escape 

 suspicion. Each letter of the alphabet corresponds to a variety of 

 words arranged in columns. Any word of the first column followed 

 by any of the second, and that followed by any of the third, &c., will 

 make, with the help of anon-significant word occasionally introduced, 

 a perfectly complete sense ; and by the time the last alphabet has been 

 ased, a letter on some indifferent subject has been written. Only sixty 



