CH. XIV] CEYPTOGRAPHS AND CIPHERS 305 



by introducing after every mth letter any single letter which it 

 is agreed shall be non-significant. To decipher a communication 

 so written it is necessary to know the clue word and the clue 

 number. 



Here for instance is a communication written in the above 

 cipher with the clue word smoking-cap, and with 7 as the clue 

 number: ngmJcs igrio icpss amcks cakqi gnass nxmig poasu 

 iamno cmpam inscn ogcpn cisyi kskam sssgn nncae hknoo mkhsc 

 pcmsc bgpng slaws sgigg ndiic a. In this sentence the letters 

 denoting the 79th, 80th, 81st, and 82nd cells have been used to 

 denote the end of a word, and no use has been made of the last 

 18 cells. 



Another cipher of this type is made as follows. The sender 

 and recipient of the message furnish themselves with identical 

 copies of some book. In the cipher only numerals are used, 

 and these numerals indicate the locality of the letters in 

 the book. For example, the first letter in the communication 

 might be indicated by 79-8-5, meaning that it is the 5th letter 

 in the 8th line of the 79th page. But though secrecy might 

 be secured, it would be very tedious to prepare or decode a 

 message, and the method is not as safe as some of those de- 

 scribed below. 



Another cipher of this type is obtained by the sender 

 and receiver agreeing on some common book of reference and 

 further on a number which, if desired, may be communicated 

 as part of the message. To employ this method the page of 

 the book indicated by the given number must be used. The 

 first letter in it is taken to signify a, the next b, and so on — 

 any letter which occurs a second time or more frequently 

 being neglected. It may be also arranged that after n letters 

 of the message have been ciphered, the next n letters shall be 

 written in a similar cipher taken from the pth following page 

 of the book, and so on. Thus the possession of the code-book 

 would be of little use to anyone who did not also know the 

 numbers employed. It is so easy to conceal the clue number 

 that with ordinary prudence it would be almost impossible for 

 an unauthorized person to discover a message sent in this cipher. 

 B.E. 20 



