The distinction between the route cipher (transposition) and the substitution cipher where whole words are substituted for letters of the original text, must be made on the basis of the words actually used. It is better to consider such a message as a route cipher when the words used appear to have some consecutive meaning bearing on the situation at hand. A substitution cipher of this variety would only be used for transmission of a short message of great importance and secrecy, and then the chances are that certain words corresponding to A, E, N, O and T would appear with such frequency as to point at once to the fact that a substitution cipher was used. Watch the initial or terminal letters in such a cipher; they may spell the message. In general, the determination of class by proportion of vowels, common consonants and rare consonants may be safely followed. We will now proceed to the examination of the more common varieties of each class of cipher. CHAPTER V EXAMINATION OF TRANSPOSITION CIPHERS After having decided that a cipher belongs to the transposition class, it remains to decide on the variety of cipher used. As, by definition, a transposition cipher consists wholly of characters of the original message, rearranged according to some law, we may, in general, say that such a cipher offers fewer difficulties in solution than a substitution cipher. A transposition cipher is like a picture puzzle; the parts are all there and the solution merely involves their correct arrangement. Case 1.--Geometrical ciphers. This case includes all ciphers in which a certain number of the characters are chosen so that they will form a square or rectangle of predetermined dimensions; and then these characters are arranged according to a geometrical design. Taking the message: A B C D E F G H I J K L M N O P Q R S T U V W X of twenty-four letters and assuming a rectangle of six letters horizontally, and four letters vertically, we may have: (a) Simple Horizontal: A B C D E F F E D C B A S T U V W X X W V U T S G H I J K L L K J I H G M N O P Q R R Q P O N M M N O P Q R R Q P O N M G H I J K L L K J I H G S T U V W X X W V U T S A B C D E F F E D C B A (b) Simple Vertical: A E I M Q U D H L P T X U Q M I E A X T P L H D B F J N R V C G K O S W V R N J F B W S O K G C C G K O S W B F J N R V W S O K G C V R N J F B D H L P T X A E I M Q U X T P L H D U Q M I E A (c) Alternate Horizontal: A B C D E F F E D C B A X W V U T S S T U V W X L K J I H G G H I J K L M N O P Q R R Q P O N M M N O P Q R R Q P O N M L K J I H G G H I J K L X W V U T S S T U V W X A B C D E F F E D C B A (d) Alternate Vertical: