Colonel A——­ (the reader will learn why I give neither his name nor real rank) spoke with some bitterness of the inquisitiveness which rendered it impossible, he said, to trust an American with a secret, and very difficult to keep one without lying.  We were presently joined by Major B——­, who had been employed during the war in the conduct of many critical communications, and had shown great ingenuity in devising and unravelling ciphers.  On this subject a somewhat protracted discussion arose.  I inclined to the doctrine of Poe, that no cipher can be devised which cannot be detected by an experienced hand; my friends indicated simple methods of defeating the processes on which decipherers rely.

“Poe’s theory,” said the Major, “depends upon the frequent recurrence of certain letters, syllables, and brief words in any given language; for instance, of e’s and t’s, tion and ed, a, and, and the in English.  Now it is perfectly easy to introduce abbreviations for each of the common short words and terminations, and equally easy to baffle the decipherer’s reliance thereon by inserting meaningless symbols to separate the words; by employing two signs for a common letter, or so arranging your cipher that no one shall without extreme difficulty know which marks stand for single and which for several combined letters, where one letter ends and another begins.”

After some debate, Colonel A——­ wrote down and handed me two lines in a cipher whose character at once struck me as very remarkable.

“I grant,” said I, “that these hieroglyphics might well puzzle a more practised decipherer than myself.  Still, I can point out even here a clue which might help detection.  There occur, even in these two lines, three or four symbols which, from their size and complication, are evidently abbreviations.  Again, the distinct forms are very few, and have obviously been made to serve for different letters by some slight alterations devised upon a fixed rule.  In a word, the cipher has been constructed upon a general principle; and though it may take a long time to find out what that principle is, it affords a clue which, carefully followed out, will probably lead to detection.”

“You have perceived,” said Colonel A——­, “a fact which it took me very long to discover.  I have not deciphered all the more difficult passages of the manuscript from which I took this example; but I have ascertained the meaning of all its simple characters, and your inference is certainly correct.”

Here he stopped abruptly, as if he thought he had said too much, and the subject dropped.

We reached New York early in the morning and separated, having arranged to visit that afternoon a celebrated “spiritual” medium who was then giving seances in the Empire City, and of whom my friend had heard and repeated to me several more or less marvellous stories.  Our visit, however, was unsatisfactory; and as we came away Colonel A——­ said—­