_Concealment of terminations._--To evade the discovery of the key or keys employed, it is most important that the termination of the words of a message should be concealed. The best method to conceal the beginning, and at the same time the termination of words, is to divide them into arbitrary groups of four or five letters each. This procedure will add immeasurably to the strength of the cipher and should in no way confuse one in possession of the key. For instance, the words "sufficient time" would be divided "suff" "icie" "ntti" "me," and such blind letters as may be agreed upon to fill the last two spaces of the last group. All such artifices as this will surely delay a translator not in possession of the key. CIPHER APPARATUS. _The cipher disk._--The cipher disk is composed of two disks of cardboard, leather, or other material joined concentrically, the upper disk revolving upon the lower. The alphabet, reading from left to right, and such other signals, numerals, or combinations of letters, as may be desired, are printed around the circumference of the lower disk. On the upper disk are printed the alphabet and such other signals, numerals, or combinations of letters as are printed on the lower disk. On the lower disk they are printed from left to right, while on the upper disk they are printed from right to left. If it is desired to encipher a message, the key letter or the first letter of the key word or words is set opposite "A." Let us assume it to be "J." The cipher letters to be written are those opposite the text letter when the letter "a" on the upper disk is set opposite "J" on the lower disk. For example, "Send powder" would be written "rfwg uvngfs." Having a cipher disk as above described, this mere transposition of letters would delay but a short time the deciphering of a message by one not knowing the key letter, as it would be necessary only to place, in turn, opposite "a" each of the letters of the alphabet beginning with "b" and noting the letters opposite the enciphered letters. But this simple disk can be used with a cipher word, or preferably, cipher words known only to the correspondents, and it is entirely improbable that a message so enciphered could be deciphered in time to be of any value to the enemy. Using the key words "permanent body" to encipher the message "Reenforcements will reach you at daylight," we would proceed as follows: Write out the message to be enciphered and above it write the key word or key words, letter over letter, thus: PERMANENTBODYPERMANENTBODYPERMANENTB Reenforcementswillreachyouatdaylight yanzvznlppkqfxijbBpwanruqpeplomccwhmi