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 cipher 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 interwoven 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 Guilletiere, in his Lacedemon ancient and modern, endeavours to make the ancient Spartans the inventors of the art of writing in cipher. Their system, according to him, was the first sketch of this mysterious art: these systemae 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 systemae which they had reserved, and in this state wrote their intentions, which appeared perfect and consistent while the parchment continued on the roll: when taken off, the writing was maimed, and without connexion, but was easily retrieved by the general, upon his applying it to his systemae.

Polybius says, that Æneas Tacticus, 2000 years ago, collected together 20 different manners of writing so as not to be understood by any but those in the secret; part whereof were invented by himself, and part used before his time.—Trithemius, Cap. Porta, Vigenere, and P. Niceron, have written 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 written in English.

1. Observe the letters or characters that most frequently occur, and set them down for the five 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 familiar 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, as, at, if, in, is, it, he, me, my, us, we, 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, his, her, our, who, may, can, did, was, are, has, had, let, one, two, five, ten, etc.—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, Cipher.

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, where, while, since, there, 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, fl, fb, fl, th, tr, wh, wr, &c. and the most common prepositions are com, con, de, dis, ev, im, in, int, mis, per, pre, 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, rt, xt, xi, &c. and the most common terminations are ed, en, er, es, et, ing, ly, ion, ion, tion, able, ence, ent, ment, full, left, nef, &c.

On Plate CXLIV. in Vol. V. 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 ob- serve 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 ob- serving 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 written in cipher is, the more easy it is to decipher, as then the repe- titions 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.

enil eno ton dna shtnom elohw eehrt, suoidifrep dna leure o noituaec & cenedurp fo klat llhw uoy : on, rotlart, teclgen & cenereffidni si ti. yltrohs rettel a emi dnes ot snaeem emof dnif rehtic, trach eht morf semoc ti taht ees em tel &c. erom ecaf ym ees ot erad reven ro.

evelvft fo ruoh cta thgin siht, ledatic eht fo etag eht eroeb elbmefla llhw sdneif ruo lau. ruoh eht ot lautcup eb : deraperp llew emoc dna, ytrebil ruoy niager ot, ylewarb eid ro. thgin eht si siht, su sekam rehtie taht, etluq su seodnu ro.

Contrivances for communicating intelligence by Cipher.

I. By means of a pack of cards. The parties must pre- viously agree in what manner the cards shall be first placed, and then how they shall be shuffled. Thus sup- pose the cards are to be first placed in the order as here- after follows, and then shuffled by taking off 3 from the top, putting the next 2 over them, and the following 3 under them*, and so alternately. Therefore the par-.* By shuf- fy who sends the cipher first writes the contents of it fling the cards in this on a separate paper, and then copies the first 32 letters on the cards, by writing one letter on every card; he there will then shuffle them, in the manner described, and writes remain- the second 32 letters: he shuffles them a second time, ly 2 to put and writes the third 32 letters, and so of the rest. An last example will make this plain. Suppose the letter to be as follows.

I am in full march to relieve you; within three days I shall be with you. If the enemy in the mean time should make an assault, remember what you owe to your country, to your family, and yourself. Live with honour, or die with glory.

Order of the cards before the first shuffle.

Ace spade i a d u y i Ten diamonds a l e u l Eight hearts m l m o i u King spades i s u m t Nine clubs n b l e o Seven diamonds f b m r i Nine diamonds u e a c t n Ace clubs l w k r y i Knave hearts l s e e a e Seven spades m i a r m w Ten clubs a i t h e r Ten hearts r r b o f Queen spades e b e e i Eight diamonds b a b y w Eight clubs t y o o o l Seven hearts o y a o o b Queen clubs r o n u y h Nine spades e u i y f y King hearts l e t e u o Queen diamonds i d s o e Eight spades e i n w s o Knave clubs v f a n t g Seven clubs e t s l y Ace hearts y r e b r Nine hearts o l n w o t Ace diamonds u h s t d Knave spades w l m a l Ten spades i e y t r r King diamonds t i i b u r Queen hearts b b m m u King clubs i n a t b Knave diamonds n e u r o

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. it would make the cipher still more difficult to dis- cover; Cipher: 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 there written with sympathetic ink, the cards might then pass for a common pack.

II. By a dial. On a piece of square pasteboard ABCD, fig. 3, draw the circle EFGH, and divide it into 26 equal parts, in each of which must be written 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 written 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 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 these 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 written one of the letters of the alphabet, and on the anterior circle ILMN, moveable round the centre 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 sol, 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 included in a letter about common affairs, and pass unsuspected.