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of the imperial yard, for the Toise employed by M. Bessel; the general size of the apparatus would be reduced to a more con venient dimension, and the diminished length of the longer pendulum would cause the coincidences with it to be observed with greater facility and increased accuracy.

Were this the proper occasion, some other modifications which have suggested themselves in M. Bessel's apparatus might be pointed out; but, by so doing, this paper would be extended to an inconvenient length. I shall confine myself, therefore, to noticing that the yacuum apparatus will probably prove a useful auxiliary in M. Bessel's method, as well as in Captain Kater's; by furnishing, in the most satisfactory manner, for the experimental pendulums of that apparatus, the amount of the retardation occasioned by the medium in which the vibration takes place.

EDWARD SABINE.

On a New Mode of Secret Writing.
By RICHARD PENN, Esq.

THE articles on the subject of Secret Writing which appeared some years ago in the Quarterly Journal of Science, induced me at that time to complete the arrangement of a cipher, founded on a principle which I had long before intended to apply to that object.

As the talent and perseverance of the decipherer have very frequently overcome all the difficulties which skill and ingenuity have opposed to the success of his labours, it may seem presumptuous that I should venture to challenge any person to unravel the intricacies which are supposed by me to belong to a cipher of my own construction. There are, however, many observations in the articles above referred to, which make me less diffident than I should otherwise have been as to the merits of the present plan, and confidently persuade me that it will be found to possess many advantages which do not appear to have been hitherto combined.

* Vol. x. p. 89, 90, 91, 101.-Vol. xii. p. 21, 29, 292, 293.

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of the imperial yard,' for the Toise employed by M. Bessel; the general size of the apparatus would be reduced to a more con venient dimension, and the diminished length of the longer pendulum would cause the coincidences with it to be observed with greater facility and increased accuracy.

Were this the proper occasion, some other modifications which have suggested themselves in M, Bessel's apparatus might be pointed out; but, by so doing, this paper would be extended to an inconvenient length. . I shall confine myself, therefore, to noticing that the vacuum apparatus will probably prove a useful auxiliary in M. Bessel's method, as well as in Captain Kater's; by furnishing, in the most satisfactory manner, for the experimental pendulums of that apparatus, the amount of the retardation occasioned by the medium in which the vibration takes place.

EDWARD SABINE,

On á New Mode of Secret Writing.

By Richard Penn, Esq. The articles on the subject of Secret Writing which appeared some years ago in the Quarterly Journal of Science *, induced me at that time to complete the arrangement of a cipher, founded on a principle which I had long before intended to apply to that object.

As the talent and perseverance of the decipherer have very frequently overcome all the difficulties which skill and ingenuity have opposed to the success of his labours, it may seem presumptuous that I should venture to challenge any person to unravel the intricacies which are supposed by me to belong to a cipher of my own construction. There are, however, many observations in the articles above referred to, which make me less diffident than I should otherwise have been as to the merits of the present plan, and confidently persuade me that it will be found to possess many advantages which do not appear to have been hitherto combined.

* Vol. x. p. 89, 90, 91, 101.- Vol. xii. p. 21, 29, 292, 293,

No cipher can be practically useful, unless the two following conditions are complied with, viz. :

That it should not be laborious to read or to write.

That it should be very difficult to be deciphered. In order to prove clearly how far the first-mentioned condition is now really complied with, it would be necessary that I should disclose the system, according to which the false letter employed is substituted for the letter which it represents; and that I should likewise explain the peculiar facility afforded to that substitution, by a mode of arrangement which is entirely new,

I must therefore confine myself to stating, in support of any claim to merit which the cipher may have on this score, that in using it, no effort of memory is required, nor any tedious reference to what is usually termed a key: all that is necessary to the use of it may be learned in a few minutes, and cannot be forgotten. There is no positive necessity that the matter should be previously written down, in order to its being put into cipher; no characters are used but the common letters of the alphabet, and the signs (+) (-) and (=); so that the difficulty, loss of time, and liability to error, necessarily attendant on the writing of unusual characters, (requiring the greatest nicety of shape and position,) are entirely avoided. The fulfilment of this condition must therefore rest upon these assertions alone.

The question as to the other condition may, however, be more satisfactorily determined, by adopting the plan pursued by Mr. Chenevix, in the paper* published by him. With this view, I do not hesitate to offer a reward of Fifty Pounds to the first person who shall, within three months from this date, decipher the annexed page.

The following are, however, the only aids which I propose to give to the person who may undertake to decipher it. The information will probably be of less value than that offered to him under the same circumstances by Mr. Chenevix t; but it must be admitted, that it is such as to expose the security of the plan to as severe a test as could ever, in common practice, be applied to it.

* Journal of Science, vol. x. p. 89.

** Ibid. p. 96, 101,

“ The matter is in English: it is a despatch from a general officer, commanding an army in the field; it is full of the phrases in common use on such occasions. The

page

does not contain more letters and signs than there are letters in the words represented; and all the smallest particles are inserted."

Every degree of fair play and encouragement is thus given to those who have maintained that any large quantity of matter ciphered on the principle of literal substitution, is not capable of concealing the process employed by the cipherer.

In the case of more complicated (but less practically useful) ciphers, a much greater degree of assistance might, perhaps, without fear of detection, be given to the decipherer; but it should be remembered, that the great facility of use possessed by this cipher, will more than compensate for the want of any further appearance of security which might be falsely given to it by more inviting explanations; and it cannot in fairness be expected, that the system should be submitted to experiment under disadvantages not properly belonging to it, but added merely in order to afford a further clue towards the attainment of that object which it is the very purpose of the cipher to defeat.

An experiment, nearly similar to the present, was made on a smaller scale with this cipher in the year 1823; and it has lately been employed in a private correspondence. The practical experience thus gained, has led to much improvement in the facility of using it, so that the condition of its not being laborious to read or to writeis completely fulfilled.

Whether or not it will also be found “ very difficult to be deciphered,remains to be proved by the severity of the test to which that condition is now submitted. If it should really possess that internal principle of security which is supposed to belong to it, it may be stated in addition, that the mischief attending the loss or seizure of one cipher would extend only to the particular correspondence in which it had been used; the principle on which it is founded being capable of such endless variety, that a correspondence might be carried on with almost any number of persons, each of whom would

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