When a dispatch or communication runs great risk of falling into the hands of the enemy, it is necessary that its contents should be so veiled that the possession of the document may afford him no information whatever. Julius Cæsar and Augustus used ciphers, but they were of the utmost simplicity, as they consisted merely in placing D in the place of A; E in that of B and so on; or else in writing B for A, and C for B, &c. Secret characters were used at the Council of Nicæa; and Rabanus Maurus, Abbot of Fulda and Archbishop of Mayence, in the Ninth Century, has left us an example of two ciphers, the key to which was discovered by the Benedictines. It is only a wonder that any one could have failed to unravel them at the first glance. This is a specimen of the first:— .Nc.p.tv:rs:.:sB::nf:c..:rch.gl::r::s.q:.::m: rt.r.s The clue to this is the suppression of the vowels and the filling of their places by dots—one for i, two for a, three for e, four for o, and five for u. In the second example, the same sentence would run—Knckpkt vfrsxs Bpnkfbckk, &c., the vowel places being filled by the consonants—b, f, k, p, x. By changing every letter in the alphabet, we make a vast improvement on this last; thus, for instance, supplying the place of a with z, b with x, c with v, and so on. This is the very system employed by an advertiser in a provincial paper, which we took up the other day in the waiting-room of a station, where it had been left by a farmer. As we had some minutes to spare, before the train was due, we spent them in deciphering the following:— Jp Sjddjzbrza rzdd ci sijmr. Bziw rzdd xrndzt, and in ten minutes we read: “If William can call or write, Mary will be glad.” When the Chevalier de Rohan was in the Bastile his friends wanted to convey to him the intelligence that his accomplice was dead without having confessed. They did so by passing the following words into his dungeon written on a shirt: “Mg dulhxecclgu ghj yxuj; lm et ulge alj.” In vain did he puzzle over the cipher, to which he had not the clue. It was too short; for the shorter a cipher letter, the more difficult it is to make out. The light faded, and he tossed on his hard bed, sleeplessly revolving the mystic letters in his brain; but he could make nothing out of them. Day dawned, and with its first gleam he was poring over them; still in vain. He pleaded guilty, for he could not decipher “_Le prisonnier est mort; il n’a rien dit_.”