The numbers represented the flashes which had followed at intervals of a second; the short dashes represented intervals of five seconds, the long dashes intervals of twenty seconds. What was the explanation? It was clear that the signalers had a code; the flashes in some way spelt out words, and Jack guessed from the long time the message had taken that the words were spelt in full. How was he to set about finding out what they were? He had never in his life read a cipher, and for some minutes he was at a loss how to begin.
At last it struck him that the highest number he had written was 20. There were twenty-six letters in the alphabet, and some of the letters, such as Q, X, Z, were very seldom used. It was not unlikely that in a comparatively short message they would not be used at all. Each letter might be represented by a number. He wrote down the twenty-six letters of the alphabet, placing a number under each, from 1 to 26. Then he substituted the letters for the numbers on the paper, thus:
QCRB——AQQCTB——P——K——OATCQB
This was nonsense; the fact that most of the letters were consonants, and the one that most frequently occurred, Q, showed that he was on the wrong tack. He must try again. He was sure the long dashes represented the intervals between the words; what did the numbers stand for?
"I wonder what letter is most often used?" he thought. He wrote down the first thing that occurred to him, the first line of the song, Heart of Oak—
"Come, cheer up, my lads, 'tis to glory we steer."
"'Tis E!" he said to himself. "It occurs in four words out of ten. Now there are three words in the stuff that have 3 and 2 in them; depend upon it either 3 or 2 stands for E. Which is it? Why, E is the second vowel, and I is the third. Every word has one or two vowels in it, and two of these words have I in them. Perhaps the five vowels are numbered 1, 2, 3, 4, 5. Let's try that."
Recopying the alphabet, he found that on this system the message read—
PIQE——APPISE——N——H——MASIPE
"It looks a little more pronounceable, but hanged if I can make any sense of it. There's a French look about it. Why, what a dolt I am! If it's Fronsac who's signaling from the Folly, of course the message will be in French. Not that that helps matters!" he thought dolefully. "The French alphabet's the same as the English till you get to W, and W is number 23, which doesn't come in. Confound the thing!"