The key may be changed from time to time, and a different key may be used with each correspondent. The utmost accuracy is necessary, because one character accidentally omitted changes the whole cypher. The best way of determining the key word is to arrange that any word which occurs at a certain distance from the beginning or end shall be the key word—the tenth from the beginning, for example. The key word will thus change every time, and any combination of letters will make it. This will make it impossible to be guessed.
The easiest method of working this square is to cut a piece of thin wood like a carpenter's square, and by applying it to the alphabet the letter is at once seen in the angle. For example, supposing such a square to be applied so that one side is on the letter p at the top, and the other on the letter w at the left hand, the letter m will be in the angle, so that the trouble of following the lines with the eye will be avoided.
Here is another specimen of secret writing.
A LOCK FOR MR. HOBBS TO PICK.
T:2 21rt:(,)t:2 s21(,)t:2 st1rr6 s,6(,)
1r2 86p : 2rs wr3t 76 : 1-9 93v3-2(,)
T : 1t : 1-9 w:38: t5-29 t:23r : 1r ? 4-6(,)
1-9 7192 t:23r v1r329 .!4r325 s:3-2(:)
3- t:2? 22- :21t:2-s 262 ?16 s22
S6?74!s 3- 5-2 .r1-9 tr3t: 84?75-2(;)
76t 3- t:2 744, 40 744,s t:2r2 !32s
1 ,26 34 r219 t:23r ?6st2r32s (.)
T:2- !2t -4t 013t:!2ss t4-.52 19v1-82
3ts s:1!!4w v15-ts(,)-4r s84002r 91r2
5p4- t:2 71sl2 40 3.-4r1-82
T4 r13s2 1 str58t5r2 40 92sp13r(!)
T:45.: 044!s ?16 .3v2 t:2 w4r!9s t4 8:1-82(,)
92s3.- 1-9 pr4v392-82 1r2 t:2r2(.)
:4w 7!3-929(,)w:4 1t 921t: 1!4-2
T:23r 922p s3.-30381-86 4w-(!)
HERE IS THE ANSWER.
The letters are represented by the figures and symbols below them. With this key the lock may be opened.
a b c d e f g h i j k l m n o u y
1 7 8 9 2 0 . : 3 ; , ! ? - 4 5 6
The stops enclosed in brackets, are used in their capacity of stops: thus, (,) (;) &c.