“I confess that I am unable to see it,” answered Harry. “We have already ascertained that by that method we get, first of all, the numbers 49, 37, and 38, and, as I remarked, we have no letters corresponding to those numbers.”
“No, I agree with you there,” replied Roger. “But how are we to know that José selected the number 1 for his letter A, 2 for the letter B, and so on? It is not very likely that he would, as that method of procedure would make the solving of the cipher a fairly easy matter, and we should have translated it by now. It is much more likely that he took some other number for his letter A, say 15, or 40, or any number rather than 1.”
Harry retorted: “Well, in that case we are just as far off the solution as at first, for how can we possibly tell, except by experiment, what numbers correspond to the right letters? And it would take us weeks to discover it by that method.”
“I agree with you that we certainly should be a very considerable time in arriving at the solution if we tried to do it simply by experiment,” said Roger. “But I do not propose to set about it in that way. Now think, Harry, what letter occurs most frequently in the English tongue.”
“Well,” replied his friend, “I have never given any thought to the matter, so I couldn’t say immediately; but I should say that the letter A occurs as often as any.”
“It certainly does often occur, as you say,” agreed Roger; “but the letter E occurs more often than any other letter, and, knowing that, I am going to look for the number that occurs most often in the cipher, and I feel sure that that number will be found to correspond to the letter E, provided always, of course, that this cryptogram is written in English.”
“Bravo, Roger,” shouted Harry; “well thought of! Now, I should never have hit upon that method if I had been worrying at this thing for ever.”
“S-s-sh—!” Roger whispered. “Be quiet, man; do you want to bring those spies and jailers upon us? For you assuredly will, if you make much of that row.”
“I am sorry,” said Harry. “For the moment I had forgotten where we were, and I felt so sure that you had hit upon the right method of translating the cipher that I shouted without thinking.”
Roger interrupted his friend: “Do not speak for a few moments. Even then I thought I caught the sound of some person outside the door; I pray Heaven that they may not come into the cell!”