"Granted. I merely select two words at random which can be coded on my incomplete square. If I had the whole diagram drawn out the message could be anything you like." "Go on," commanded Betty, her eyes snapping. "First you write down your message; then above it you put the key-word, repeated in whole or in part as many times as may be necessary, thus:" B E A D B E A C A B F E E D "Turning to the diagram you find B, the first letter of the key-word, in the top horizontal line; and C, the first letter of the word to be put into code, in the left-hand vertical line. Now look for the letter at the intersection of the vertical column headed by B and the horizontal line which C begins. You will find it to be E. Set this down as the first symbol of your cypher message, and obtain the other letters in a similar manner. Your despatch will then read: E F C J G J E. As an object lesson, place these letters under your original arrangement of key-word and message, thus:" B E A D B E A C A B F E E D E F C J G J E "You see at a glance that the substitution is irregular and variant. For example, the symbol E stands for both C and D. Again, the letter E in the word F E E D is at one time represented by G and secondly by J." "How do you translate the cypher?" asked Betty. "Merely reverse the process. You write down the cypher message, and above it as many letters of your key-word as may be needed, thus:" B E A D B E A E F C J G J E "Now follow down the vertical column headed by B until you reach the symbol letter E; then move your pointer over left to the end of that horizontal line which will give you C, the first letter of the original message. Understand?" Betty tried her hand, and quickly caught the trick; really it was very easy. "One more point; it is better not to divide the cypher message into word groups as the continuous string of letters looks more mystifying. There is no difficulty in picking out the sense when decoding." "Finally, you notice that the upper left-hand space in the diagram is vacant; consequently you must not use the letter Z in either the key-word or in the message to be coded. But this restriction is not of any practical disadvantage, Z being a letter that is seldom used. It will often appear, of course, in the cypher itself." "Certainly it is all very simple," remarked Betty. "But without the key-word where would you get off?" "I don't see how anybody could possibly work it out; why the complications are absolutely overwhelming." "And you can make them still more intricate by merely using a longer key-word, or indeed a whole sentence. For example: 'I love Betty Hildebrand.'" "Everybody knows that," retorted Betty. "Still I don't mind an occasional restatement of the established fact. Please, Hugh! I spent any amount of time in getting those ruffles starched just so."