Place "a" of the upper cipher disk under B of the lower disk and notice whether the cipher letters jbfo—the first group—are intelligible. They give "sawn," continue this for "saw," the first three letters, may be the text word. Now the next group is B N Y R and these give A O D K. We know that A does not represent B because the first 8 cipher letters give the meaningless letters "sawnaodk." Turn "a" to C and we have for the first group T B X O, which is without meaning. Turning "a" to D we get U C Y P, a meaningless jumble. Turn "a" to E and we get V D Z Q, which is meaningless. Now turn "a" under F and we find that JBFO mean "Wear," which, so far at least, gives us a part of a word, or the word "We" and part of another word. We continue to the next group B N Y R, which gives us "esho." We now have these letters "Wearesho," which at a glance we read "We are sho;" continuing to the next group O M R A the cipher disk gives us "rtof," and we read "We are short of" and know we have found the key letter, and the information hidden in the cipher is ours. Continue deciphering with "a" under F until the end of the message. Sometimes the key letter is changed after two, three, or four letters.
It is a matter of minutes only to run through the alphabet and learn the meaning of a message so enciphered.
Chapter VII.
FIELD GLASSES AND TELESCOPES.
Reflection—refraction—lenses.
