Page:Passages from the Life of a Philosopher.djvu/253

Rh 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