DORIS AND MARJORIE GIVE A SUPPER PARTY. THE ARROW FLIES IN MORSTONE SEA WOOD
"This," said my brother, "is what is known as Charles Wheatstone's Cipher Instrument. It is a machine for writing in cipher. You see it has a sort of watch-face, which has the alphabet inscribed round its outer margin in the usual order, plus a blank space. A second alphabet is written on a card or paper and attached to the watch-face within the first alphabet. This has no blank space, and so there are but twenty-six divisions as against twenty-seven in the outer ring. Two hands are attached which travel at different speeds when the handle is turned. Accordingly, each time the long hand is carried forward to the blank space at the end of a word, the short hand will have moved forward one division on the inner ring of letters. Then a word is chosen as a key, written down in separate letters and the remaining letters of the alphabet are written in order beneath it. I'll show you. Suppose, for example, we choose the word 'English,' thus." He took a pencil and scribbled for a moment upon the back of one of Dickson's photographs:
ENGLISH
ABCDFJK
MOPQRTU
VWXYZ.
"Now, if you read these letters downwards, you get this arrangement:
EAMVNBOWGCPXLDQYIFRZSJTHKU.
"This cryptographic alphabet is written on the inner card of the instrument, beginning at a point previously agreed on. Then, when a despatch is to be translated into cipher, the long hand is moved to that letter in the outer alphabet, and the letter to which the short hand points in the inner ring is written down. I need not go on, but I am sure the principle will be clear to you. These machines are in use in our Secret Service. But what I should like to point out to you in regard to this example is that the alphabet here is in German."
