or Cypher, one of the Arabic characters or figures used in computation, formed thus, o. See Arithmetic.

Cipher is also a kind of enigmatic character, composed of several letters interwoven, which are generally the initial letters of the persons names for whom the ciphers are intended. These are frequently used on seals, coaches, and other moveables.—Anciently, merchants and tradesmen were not allowed to bear arms: in lieu thereof, they bore their ciphers, or the initial letters of their names, artfully interwove about a cross; of which we have divers instances on tombs, &c. See Devise.

Cipher, denotes likewise certain secret characters disguised and varied, used in writing letters that contain some secret, not to be understood but by those between whom the cipher is agreed on.

De la Guetteiere, in his Lacedemon ancient and modern, endeavours to make the ancient Spartans the inventors of the art of writing in cipher. Their scitata, according to him, was the first sketch of this mysterious art: these scitata were two rollers of wood, of equal length and thickness; one of them kept by the ephori; the other by the general of the army sent on any expedition against the enemy. Whenever those magistrates would send any secret orders to the general, they took a slip of parchment, and rolled it very justly about the scitata which they had reserved; and in this flate wrote their intentions, which appeared perfect and consistent while the parchment continued on the roller: when taken off, the writing was maimed, and without connection; but was easily retrieved by the general, upon his applying it to his scitata.

Polybius says, that Aeneas Tacitus, 2000 years ago collected together 20 different manners of writing so as not to be understood by any but those in the cipher; part whereof were invented by himself, and part used before his time.—Trithemius, Cap. Porta, Vigenere, and P. Niceron, have wrote expressly on the subject of ciphers.

As the writing in cipher is become an art; so is the reading, or unravelling thereof, called deciphering.—The rules of deciphering are different in different languages. By observing the following, you will soon make out any common cipher wrote in English.

1. Observe the letters or characters that most frequently occur; and set them down for the six vowels, including y; and of these the most frequent will generally be e, and the least frequent u.

2. The vowels that most frequently come together are ea and ou.

3. The consonant most common at the ends of words is s, and the next frequent r and t.

4. When two similar characters come together, they are most likely to be the consonants f, l, or s, or the vowels e or o.

5. The letter that precedes or follows two similar characters is either a vowel, or l, m, n, or r.

6. In deciphering, begin with the words that consist of a single letter, which will be either a, i, o, or u.

7. Then take the words of two letters, one of which will be a vowel. Of these words the most frequent are, an, to, be, by, of, on, or, no, so, ai, et, if, in, it, it, he, me, my, ui, wi, am.

8. In words of three letters there are most commonly two consonants. Of these words the most frequent are, the, and, not, but, yet, for, tho’, how, why, all, you, she, hit, her, our, who, may, can, did, was, are, has, had, let, one, two, six, ten, &c.*

* Some of these, or those of two letters, will be found in every sentence. 9. The most common words of four letters are, this, that, then, thus, with, when, from, here, some, most, none, they, them, whom, mine, your, self, must, will, have, been, were, four, five, nine, &c.

10. The most usual words of five letters are, there, these, those, which, were, while, since, their, shall, might, could, would, ought, three, seven, eight, &c.

11. Words of two or more syllables frequently begin with double consonants, or with a preposition; that is, a vowel joined with one or more consonants. The most common double consonants are bl, br, dr, fl, fr, gl, gr, ph, pl, pr, sh, sp, th, tr, wh, wr, &c., and the most common prepositions are con, com, de, dis, ex, im, in, int, mit, par, per, pro, re, sub, sup, un, &c.

12. The double consonants most frequent at the end of long words are, ck, ld, lf, mn, nd, ng, rl, rm, rn, rp, rt, sn, st, xt, &c., and the most common terminations are ed, en, er, es, ing, ly, on, ion, tion, able, ance, ent, ment, full, left, ngs, &c.

On Plate LXXIX. fig. 7. is given an example of a cipher wrote in arbitrary characters as is commonly practised. It will be easily deciphered by observing the rules: but when the characters are all placed close together, as in the example fig. 8. and as they always should be, the deciphering is much more difficult.

To decipher a writing of this sort you must first look for those characters that most frequently occur, and set them down for vowels as before. Then observe the similar characters that come together; but you must remember that two such characters may here belong to two words. You are next to remember the combinations of two or three characters that are most frequent; which will be some of the words in the seventh and eighth of the foregoing rules; and by observing the other rules, you will infallibly discover, with time and attention, any cipher wrote on these principles.

When the words are wrote all close together, if the key to the cipher were to be changed every word, according to a regular method agreed on between the parties, as might be done by either of the methods mentioned in No II. below, with very little additional trouble, the writing would then be extremely difficult to decipher. The longer any letter wrote in cipher is, the more easy it is to decipher, as then the repetitions of the characters and combinations are the more frequent.

The following are the contents of the two foregoing ciphers; in which we have inverted the order of the words and letters, that they who are desirous of trying their talent at deciphering, may not, inadvertently, read the explanation before the cipher.

The person that receives these cards first places them in the order agreed on, and transcribes the first letter on every card. He then shuffles them, according to order, and transcribes the second letter on each card. He shuffles them a second time and transcribes the third letters; and so of the rest.

If the cards were to be shuffled the second time by threes and fours, the third time by twos and fours, &c. Cipher.

it would make the cipher still more difficult to discover; though as all ciphers depend on the combination of letters, there are scarce any that may not be deciphered with time and pains; as we shall show further on. Those ciphers are the best, that are by their nature most free from suspicion of being ciphers; as for example, if the letters were here wrote with one of the sympathetic inks, described in the fourth volume of this work, the cards might then pass for a common pack.

II. By a dial. On a piece of square pasteboard ABCD, fig. 3. 4. draw the circle EFGH, and divide it into 26 equal parts, in each of which must be wrote one of the letters of the alphabet.

On the inside of this there must be another circle of pasteboard, ILMN, moveable round the centre O, and the extremity of this must be divided into the same number of equal parts as the other. On this also must be wrote the letters of the alphabet, which, however, need not be disposed in the same order. The person with whom you correspond must have a similar dial, and at the beginning of your letter you must put any two letters that answer to each other when you have fixed the dial.

Exam. Suppose you would write as follows: "If you will come over to us, you shall have a pension, and you may still make a sham opposition." You begin with the letters Ma, which show how the dial is fixed: then for If you, you write un juc, and so for the rest, as you will see at fig. 6.

The same intention may be answered by a ruler, the upper part of which is fixed and the lower part made to slide; but in this case the upper part must contain two alphabets in succession, that some letter of that part may constantly correspond to one in the lower part. The divisions standing directly over each other in a straight line will be much more obvious than in the circumference of a circle. Or two straight pieces of pasteboard regularly divided, the one containing a single and the other a double alphabet, would answer exactly the same purpose. In this case a blank space may be left at each end of the single alphabet, and one or two weights being placed on both the pieces will keep them steady.

III. The corresponding spaces. Take two pieces of pasteboard or stiff paper, through which you must cut long squares, at different distances, as you will see in the following example. One of these pieces you keep yourself, and the other you give to your correspondent. When you would send him any secret intelligence, you lay the pasteboard upon a paper of the same size, and in the spaces cut out, you write what you would have understood by him only, and then fill up the intermediate spaces with somewhat that makes with those words a different sense.

I shall be much obliged to you, as reading alone engages my attention at present, if you will lend me any one of the eight volumes of the Spectator. I hope you will excuse this freedom, but for a winter's evening I don't know a better entertainment. If I fail to return it soon, never trust me for the time to come.

A paper of this sort may be placed four different ways, either by putting the bottom at the top, or by turning it over, and by those means the superfluous words may be the more easily adapted to the sense of the others.

This is a very eligible cipher, as it is free from suspicion, but it will do only for short messages: for if the spaces be frequent, it will be very difficult to make the concealed and obvious meanings agree together: and if the sense be not clear, the writing will be liable to suspicion.

IV. The musical cipher. The construction of this cipher, is similar to that of No II. The circle EFGH (fig. 3.) is to be divided into twenty-six equal parts, in each part there must be wrote one of the letters of the alphabet: and on the anterior circle ILMN, moveable round the center O, there is to be the same number of divisions: the circumference of the inner circle must be ruled in the manner of a music paper; and in each division there is to be placed a note, differing either in figure or position. Lastly, within the musical lines place the three keys, and on the outer circle, the figures that are commonly used to denote the time.

Then provide yourself with a ruled paper, and place one of the keys, as suppose that of ge re fis, against the time two-fourths at the beginning of the paper, which will inform your correspondent how to fix his circle. You then copy the notes that answer to the several letters of the words you intend to write, in the manner expressed at fig. 5.

A cipher of this sort may be made more difficult to discover by frequently changing the key, and that will not in the least embarrass the reader. You may likewise add the mark # or $ to the note that begins a word, which will make it more easy to read, and at the same time give the music a more natural aspect. This cipher is preferable to that of No II. above, as it may be inclosed in a letter about common affairs, and pass unnoticed.