The Analytical Engine


Passages from the Life of a Philosopher

F.R.S., F.R.S.E., F.R.A.S., F. STAT. S., HON. M.R.I.A., M.C.P.S.,

Picture of Charles Babbage




Interview with Vidocq—Remarkable Power of altering his Height—A Bungler in picking Locks—Mr. Hobb's Lock and the Duke of Wellington—Strong belief that certain Ciphers are inscrutable—Davies Gilbert's Cipher—The Author's Cipher both deciphered—Classified Dictionaries of the English Language—Anagrams—Squaring Words—Bishop not easily squared—Lesser Dignitaries easier to work upon.

These two subjects are in truth much more nearly allied than might appear upon a superficial view of them. They are in fact closely connected with each other as small branches of the same vast subject of combinations.

Several years ago, the celebrated thief-taker, Vidocq, paid a short visit to London. I had an interview of some duration with this celebrity, who obligingly conveyed to me much information, which, though highly interesting, was not of a nature to become personally useful to me.

He possessed a very remarkable power, which he was so good as to exhibit to me. It consisted in altering his height to about an inch and a half less than his ordinary height. He threw over his shoulders a cloak, in which he walked round the room. It did not touch the floor in any part, and was, I should say, about a inch and a half above it. He then altered his height and took the same walk. The cloak then touched the floor and lay upon it in some part or other during the whole walk. He then stood still and altered his height alternately, several times to about the same amount.

I inquired whether the altered height, if sustained for several hours, produced fatigue. He replied that it did not, and that he had often used it during a whole day without any additional fatigue. He remarked that he had found this gift very useful as a disguise. I asked whether any medical man had examined the question; but it did not appear that any satisfactory explanation had been arrived at.

I now entered upon a favourite subject of my own—the art of picking locks—but, to my great disappointment, I found him not at all strong upon that question. I had myself bestowed some attention upon it, and had written a paper, ‘On the Art of Opening all Locks,’ at the conclusion of which I had proposed a plan of partially defeating my own method. My paper on that subject is not yet published.

Several years after Vidocq's appearance in London, the Exhibition of 1851 occurred. On one of my earliest visits, I observed a very curious lock of large dimensions with its internal mechanism fully exposed to view. I found, on inquiry, that it belonged to the American department. Having discovered the exhibitor, I asked for an explanation of the lock. I listened with great interest to a very profound disquisition upon locks and the means of picking them, conveyed to me with the most unaffected simplicity.

I felt that the maker of that lock surpassed me in knowledge of the subject as much as I had thought I excelled Vidocq. Having mentioned it to the late Duke of Wellington, he proposed that we should pay a visit to the lock the next time I accompanied him to the Exhibition. We did so a few days after, when the Duke was equally pleased with the lock and its inventor. Mr. Hobbs, the gentleman of whom I am speaking, and whose locks have now become so celebrated, was good enough to explain to me from time to time many difficult questions in the science of constructing and of picking locks. He informed me that he had devised a system for defeating all these methods of picking locks, for which he proposed taking out a patent. I was, however, much gratified when I found that it was precisely the plan I had previously described in my own unpublished pamphlet.


Deciphering is, in my opinion, one of the most fascinating of arts, and I fear I have wasted upon it more time than it deserves. I practised it in its simplest form when I was at school. The bigger boys made ciphers, but if I got hold of a few words, I usually found out the key. The consequence of this ingenuity was occasionally painful: the owners of the detected ciphers sometimes thrashed me, though the fault really lay in their own stupidity.

There is a kind of maxim amongst the craft of decipherers (similar to one amongst the locksmiths), that every cipher can be deciphered.

I am myself inclined to think that deciphering is an affair of time, ingenuity, and patience; and that very few ciphers are worth the trouble of unravelling them.

One of the most singular characteristics of the art of deciphering is the strong conviction possessed by every person, even moderately acquainted with it, that he is able to construct a cipher which nobody else can decipher. I have also observed that the cleverer the person, the more intimate is his conviction. In my earliest study of the subject I shared in this belief, and maintained it for many years.

In a conversation on that subject which I had with the late Mr. Davies Gilbert, President of the Royal Society, each maintained that he possessed a cipher which was absolutely inscrutable. On comparison, it appeared that we had both imagined the same law, and we were thus confirmed in our conviction of the security of our cipher.

Many years after, the late Dr. Fitton, having asked my opinion of the possibility of making an inscrutable cipher, I mentioned the conversation I had had with Davies Gilbert, and explained the law of the cipher, which we both thought would baffle the greatest adept in that science. Dr. Fitton fully agreed in my view of the subject; but even whilst I was explaining the law, an indistinct glimpse of defeating it presented itself vaguely to my imagination. Having mentioned my newly-conceived doubt, it was entirely rejected by my friend. I then proposed that Dr. Fitton should write a few sentences in a cipher constructed according to this law, and that I should make some attempts to unravel it. I offered to give a few hours to the subject; and if I could see my way to a solution, to continue my researches; but if not on the road to success, to tell him I had given up the task.

Late in the evening of that day I commenced a preparatory inquiry into the means of unravelling this new cipher, and I soon arrived at a tolerable certainty that I should succeed. The next night, on my return from a party, I found Dr. Fitton's cipher on my table. I immediately commenced my attempt. After some time I found that it would not yield to my means of treating it; and on further examination I succeeded in proving that it was not written according to the law agreed upon. At first my friend was very positive that I was mistaken; and having taken it to his sister, by whose aid it was composed, he returned and told me that it was constructed upon the very law I had proposed. I then assured him that they must have made some mistake, and that my evidence was so irresistible, that if my life depended upon the result I should have no hesitation in making my election.

Dr. Fitton again retired to consult his sister; and after the lapse of a considerable interval of time again returned, and informed me that I was right—that his sister had inadvertently mistaken the enunciation of the law. I now remarked that I possessed an absolute demonstration of the fact I had communicated to him; and added that, having conjectured the origin of the mistake, I would decipher the cipher with the erroneous law before he could send me the new cipher to be made according to the law originally proposed. Before the evening of the next day both ciphers had been translated.

This cipher was arranged upon the following principle:—Two concentric circles of cardboard were formed, each divided into twenty-six or more divisions.

On the outer were written in regular order the letters of the alphabet. On the inner circle were written the same twenty-six letters, but in any irregular manner.

In order to use this cipher, look for the first letter of the word to be ciphered on the outside circle. Opposite to it, on the inner circle, will be another letter, which is to be written as the cipher for the former.

Now turn round the inner circle until the cipher just written is opposite the letter a on the outer circle. Proceed in the same manner for the next, and so on for all succeeding letters.

Many varieties of this cipher may be made by inserting other characters to represent the divisions between words, the various stops, or even blanks. Although Davies Gilbert, I believe, and myself, both arrived at it from our own efforts, I have reason to think that it is of very much older date. I am not sure that it may not be found in the “Steganographia” of Schott, or even of Trithemius.

One great aid in deciphering is, a complete analysis of the language in which the cipher is written. For this purpose I took a good English dictionary, and had it copied out into a series of twenty-four other dictionaries. They comprised all words of

One letter,
Two letters,
Three letters,
  &c.   &c.:
Twenty-six letters.

Each dictionary was then carefully examined, and all the modifications of each word, as, for instance, the plurals of substantives, the comparatives and superlatives of adjectives, the tenses and participles of verbs, &c., were carefully indicated. A second edition of these twenty-six dictionaries was then made, including these new derivatives.

Each of these dictionaries was then examined, and every word which contained any two or more letters of the same kind was carefully marked. Thus, against the word tell the numbers 3 and 4 were placed to indicate that the third and fourth letters are identical. Similarly, the word better was followed by the numbers 25, 34. Each of these dictionaries was then re-arranged thus:—In the first or original one each word was arranged according to the alphabetical order of its initial letter.

In the next the words were arranged alphabetically according to the second letter of each word, and so in the other dictionaries on to the last letter.

Again, each dictionary was divided into several others, according to the numerical characteristics placed at the end of each word. Many words appeared repeatedly in several of these subdivisions.

The work is yet unfinished, although the classification already amounts, I believe, to nearly half a million words.

From some of these, dictionaries were made of those words only which by transposition of their letters formed anagrams. A few of these are curious:—

Opposite   Similarity   Satirical
vote veto   fuel flue   odes dose
acre care   taps pats   bard drab
evil veil   tubs buts   poem mope
ever veer   vast vats   poet tope
lips slip   note tone   trio riot
cask sack   cold clod   star rats
fowl wolf   evil vile   wive view
gods dogs   arms mars   nabs bans
tory tyro   rove over   tame mate
tars rats   lips lisp   acts cats

There are some verbal puzzles costing much time to solve which may be readily detected by these dictionaries. Such, for instance, is the sentence,

I tore ten Persian MSS.,

which it is required to form into one word of eighteen letters.

The first process is to put opposite each letter the number of times it occurs, thus:—

i 2 p 1 It contains—
t 2 s 3   2 triplets.
o 1 a 1   4 pairs.
r 2 m 1   4 single letters.
e 3

n 2 6  18


Now, on examining the dictionary of all words of eighteen letters, it will be observed that they amount to twenty-seven, and that they may be arranged in six classes:—

7 having five letters of the same kind.
5     "       four                   "
3     "       three triplets.
7     "       two triplets.
3     "       one triplet.
2     "       seven pairs.


Hence it appears that the word sought must be one of those seven having two triplets, and also that it must have four pairs; this reduces the question to the two words—


The latter is the one sought, because its triplets are e and s, whilst those of the former are i and t.

The reader who has leisure may try to find out the word of eighteen letters formed by the following sentence:—

Art is not in, but Satan.

Another amusing puzzle may be greatly assisted by these dictionaries. It is called squaring words, and is thus practised:—Let the given word to be squared be Dean. It is to be written horizontally, and also vertically, thus:—

D e a n
e . . .
a . . .
n . . .

And it is required to fill up the blanks with such letters that each vertical column shall be the same as its corresponding horizontal column, thus:—

D e a n
e a s e
a s k s
n e s t

The various ranks of the church are easily squared; but it is stated, I know not on what authority, that no one has yet succeeded in squaring the word bishop.

Having obtained one squared word, as in the case of Dean, it will be observed that any of the letters in the two diagonals, d, a, k, t,— n, s, s, n, may be changed into any other letter which will make an English word.

Thus Dean may be changed into such words as

dear peas weak beam
fear seas lead seal
deaf bear real team

In fact there are upwards of sixty substitutes: possibly some of these might render the two diagonals, d, a, k, t, and n, s, s, n, also English words.