Crewe went to the table and picked up the plan.
“My first impression was that the circle of figures represented some form of letters of the alphabet arranged on what is called the cardboard or trellis cipher, in which a message is concealed by altering the places of the letters without changing their powers. Such messages are generally written after the Chinese fashion—upwards and downwards—but there is no reason why a circle should not be used to conceal the message. In this case I did not expect to find a message hidden in the circle, but rather, the key to the solution of the letters above the circle, which, I was convinced, formed the real cryptogram.
“The recurring T’s and M’s in the top line seemed to indicate that it was some form of changed letter cipher, complicated by having to be read in connection with the figures in the circle, which represented other letters of the alphabet. The numbers, representing an ascending series from 6 to 89, with one recurring 6, suggested the possibility of this form of cryptogram having been used. The numbers in the centre suggested a sum, which, when done, would throw some light on the arithmetical puzzle in the centre of the circle by division, subtraction, or multiplication.
“I worked for a solution on these lines for some time, but ultimately came to the conclusion that the solution did not lie within them. I am not an arithmetician, but my calculations told me enough to make me realize that I was on the wrong track.
“I next attempted to ascertain if the two mysterious messages—the lines on the top and the circle of figures—were two separate messages read independently of one another. I did not think they were, but I determined to put it to the test. Obviously, if they were, the top line was merely a changed letter cipher, and nothing more. These are usually easy to decipher because of the frequency with which certain letters recur. In English the letter that occurs oftenest is E, then T, then A, O, N, I, then R, S, H; the others in lessening frequency down to J and Z, which are the least used letters in the English alphabet. The recurring letters in our cryptogram are T’s and M’s. Using these as a basis to give me the key, I tried all likely combinations on the changed letter basis, but without success.
“I came back to my original idea that the figures in the circle were the solvent of the line of letters above, and concentrated my efforts in attempting to discover their meaning. I finally came to the conclusion that the figures represented the pages or lines of some book.”
“Like the cryptograms I used to solve when I was at school,” suggested Marsland, with a smile.
“Rather more difficult than that. In that form of cryptogram rows of figures are turned into words once you hit on the right book. This cryptogram is much more ingenious, for it consists of three parts—a line of meaningless letters and a circle of equally meaningless figures, with other figures within it, and some plain English verses of Scripture, the whole probably interdependent. If the circle of figures represented some book necessary to the solution of the whole cryptogram, the first thing to find out was the book from which the figures had been taken. I had not much difficulty in arriving at the conclusion that this book was a large brass-bound family Bible I saw at Cliff Farm.”
“I suppose the texts on the bottom of the sheet suggested that idea to you?” said Marsland.
Crewe shook his head.