hin the limits of our ken, and about which we know
nothing. But, about the key to the cryptogram, what is it? You must
tell us that, you know, Saint Leger, in consideration of our own
unsuccessful efforts to help you. Besides, the knowledge of such a
difficult cipher as that is really worth having; who can say how soon,
or under what circumstances, it might be found useful for purposes of
secret communication?"

"Oh, it is ridiculously simple, when you know it," said I. "All you
have to do is to number each letter of the alphabet consecutively,
beginning with A and calling it eleven. Then, with the cryptogram
before you, you divide the figures into series of four, each four
figures representing a letter. Subtract the first pair of figures from
the second, and the remainder gives you the number of the letter as you
have it in your key. For example: the first four figures in the
document are 1133; that is to say, eleven and thirty-three. The
difference between them is twenty-two, which, you see, represents the
letter L in the key. Then take the next four figures, treating them in
the same way, and so on throughout the document. One great advantage of
such an arrangement appears to me to be that, however many times the
same letter occurs in a document, it need never be represented twice in
exactly the same way, which certainly must greatly tend to preserve the
secrecy of the cipher. There are no spaces, you observe, to mark the
divisions between the several words; but that offers no difficulty
whatever when one possesses the key; while--to my cost I know it--it
adds tremendously to the difficulty when one does not. Then, again, the
figures of the latitude and longitude are given just as they would be in
an ordinary document, which brought me completely to a standstill for a
little while, until I happily guessed at the explanation; but after
passing these stumbling-blocks, the rest was perfectly plain sailing."

"Quite so," acquiesced Sir Edgar. "It is simple enough when it has been
explained; but a sufficiently ingenious thing for all that, in proof of
which we have the fact that it has completely puzzled us all for months;
and I really believe, Saint Leger, that, but for your wonderful dream,
it would have continued to puzzle you to the end of time. I
congratulate you heartily upon your good fortune."

"And I;" "And I," simultaneously exclaimed Lady Emily and her sister.

"And now," continued the baronet,