“We must not lose patience,” said Lecoq quietly.  He took the slip of paper from the magistrate and read the numbers inscribed upon it.  They ran as follows:  “235, 15, 3, 8, 25, 2, 16, 208, 5, 360, 4, 36, 19, 7, 14, 118, 84, 23, 9, 40, 11, 99.”

“And so we shall learn nothing from this note,” murmured the governor.

“Why not?” the smiling clerk ventured to remark.  “There is no system of cipher which can not be read with a little skill and patience; there are some people who make it their business.”

“You are right,” said Lecoq, approvingly.  “And I, myself, once had the knack of it.”

“What!” exclaimed the magistrate; “do you hope to find the key to this cipher?”

“With time, yes.”

Lecoq was about to place the paper in his breast-pocket, when the magistrate begged him to examine it a little further.  He did so; and after a while his face suddenly brightened.  Striking his forehead with his open palm, he cried:  “I’ve found it!”

An exclamation of incredulous surprise simultaneously escaped the magistrate, the governor, and the clerk.

“At least I think so,” added Lecoq, more cautiously.  “If I am not mistaken, the prisoner and his accomplice have adopted a very simple system called the double book-cipher.  The correspondents first agree upon some particular book; and both obtain a copy of the same edition.  When one desires to communicate with the other, he opens the book haphazard, and begins by writing the number of the page.  Then he must find on the same page the words that will express his thoughts.  If the first word he wishes to write is the twentieth on the page, he places number 20 after the number of the page; then he begins to count one, two, three, and so on, until he finds the next word he wishes to use.  If this word happens to be the sixth, he writes the figure 6, and he continues so on till he has finished his letter.  You see, now, how the correspondent who receives the note must begin.  He finds the page indicated, and then each figure represents a word.”

“Nothing could be clearer,” said the magistrate, approvingly.

“If this note,” pursued Lecoq, “had been exchanged between two persons at liberty, it would be folly to attempt its translation.  This simple system is the only one which has completely baffled inquisitive efforts, simply because there is no way of ascertaining the book agreed upon.  But in this instance such is not the case; May is a prisoner, and he has only one book in his possession, ‘The Songs of Beranger.’  Let this book be sent for—­”

The governor of the Depot was actually enthusiastic.  “I will run and fetch it myself,” he interrupted.

But Lecoq, with a gesture, detained him.  “Above all, sir,” said he, “take care that May doesn’t discover his book has been tampered with.  If he has returned from his promenade, make some excuse to have him sent out of his cell again; and don’t allow him to return there while we are using his book.”