Cipher disks should never be allowed to fall into the hands of the enemy or of anyone unauthorized to have and use them; to insure this, special instructions should be issued for their care and keeping. THE MATHEMATICAL CIPHER. This cipher is a highly efficient one for the purpose of secrecy and at the same time requires no apparatus whatever attendant upon its use. The cipher is constructed as follows: Commit to memory the alphabet by numbers, viz, A, 1; B, 2; etc. Take any key word, phrase, or sentence desired; for example, "A discovery." Suppose the message to be enciphered is "Send me powder tonight." The enciphering of the message using the key given above will be as follows: To encipher, first write out the key, letter by letter, placing the message letter by letter beneath it. Then reduce the letters of the key and the message to the numeral alphabetical equivalents. Add the individual columns and subtract unity from each. From any result thus found, which exceeds the number of letters in the alphabet, the number 26 must be subtracted. The final totals reduced to letters by numerical alphabetical equivalents will then give the cipher. ADISCOVERYADISCOVER sendmepowdertonight which reduced to numerical equivalents according to alphabetical position of letters becomes: 1 4 9 19 3 15 22 5 18 25 1 4 9 19 3 15 22 5 18 19 5 14 4 13 5 16 15 23 4 5 18 20 15 14 9 7 8 20 Now add the columns and subtract unity from each. If any result so found exceeds the number of letters in the alphabet 26 must be subtracted from it. In the example given the numerical totals are as follows: 20 9 23 23 16 20 38 20 41 29 6 22 29 34 17 24 29 13 38 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ------------------------------------------------------- 19 8 22 22 15 19 37 19 40 28 5 21 28 33 16 23 28 12 37 26 26 26 26 26 26 26 ------------------------------------------------------- 19 8 22 22 15 19 11 19 14 2 5 21 2 7 16 23 2 12 11 which connected to letters gives: SHVVOSKSNBEUBGOWBLK the cipher required. Translation of cipher is had by reversing the processes described. THE ROUTE CIPHER.