Chapter XIV: The Riddle Solved

In the house above the hawk's nest, four boys and a man sat far into the night, examining a marked dollar and trying to unravel the secret of the scratches. From hand to hand the dollar passed and was examined now this way, now that; but the little group could see no meaning in the apparently aimless marks on the silver coin. Had some of them not seen this dollar marked and its message deciphered and sent vibrating through the air, they would have refused to believe that the coin before them carried a message at all. It looked like any dollar that has accidentally become marked.

"To-morrow," said Captain Hardy, "we will turn the dollar over to the secret service, and doubtless their experts will solve the problem quick enough. But I certainly wish we could unravel this thing ourselves. Wouldn't it be an achievement for the wireless patrol!"

"It's going to be," declared Roy positively. "We're going to solve it. We've just got to. We'll show those secret service men that boys are some good after all."

But the word was easier than the deed. Puzzle their brains as they might, search the dollar as they would, they still found no key to the language it spoke.

"Tell me again what the message was," demanded Henry for the twentieth time, and Lew once more passed to Henry the slip of paper on which he had written the message, both in cipher and deciphered, the message he had picked from the air. It read as follows: TRPSLOWAOSEDONBADATSTITY.

T R P S L O
W A O S E D
O N R A D A
T S T I T Y

Long Henry studied the piece of paper, softly reading the message to himself. "Two transports sailed to-day. How did that automobile driver get that message from this dollar?" he asked himself, and again he picked up the coin and turned it in his hand. "If only we had that disc," he sighed, "or a duplicate."

At the word "duplicate," Roy pricked up his ears. "Maybe we can make one," he said.

"Likely!" scoffed Lew.

"You never know till you try," rejoined Roy. Then he turned to Willie and demanded, "What was the disc like that you saw?"

"If I knew, I'd make one," said Willie.

"Well," said Roy in a tone of disgust, "you know whether it was a foot across or not, and whether it was round or square."

"It was round, of course," said Willie, "and the same size as the dollar. I told you that before."

"We can make a disc the size of a dollar, anyway, even if it doesn't get us anywhere," said Roy, putting the coin on a sheet of paper and outlining it with a pencil. Then with scissors he cut the disc out.

"You saw that disc, or one like it, Henry," continued Roy. "What did it look like to you?"

"Just like a spider-web, as Willie says," replied Henry.

"All right, we'll make a spider-web," said Roy.

He seized his pencil, made a dot in the centre of the disc, and from the dot drew straight lines that radiated in different directions. Then he drew a number of concentric circles about his dot.

"I don't see how that helps any," he said, examining his drawing. "Yet that's the kind of thing they used to mark that dollar."

From hand to hand the paper passed, and each boy compared it with the dollar. But none was any the wiser when he had finished. Their leader, meantime, sat with his head in his hands, studiously turning the matter over and over in his mind. For a long time he could make nothing of it.

After a while he looked up. "Let me see that paper," he said.

Roy handed him the little disc. Captain Hardy laid the disc beside the dollar on the table, and painstakingly examined again the marks on the coin. After a time he took a sheet of paper and across it in a row wrote down the letters of the alphabet. Then he picked up the message and made check marks below the letters in his alphabet as he found those letters in the message. When he had gone through the message, his paper looked like this:

ABCDEFGHIJKLMNOPQRSTUVWXYZ
/ // / / /// /// / /
/ / / ///
/ / //
/

He picked it up and studied it. "Four T's," he said, "three S's, three A's, and three O's. That ought to give us a clue."

Again he turned to the dollar and began to study it, turning it slowly round, counting the scratches this way and that, making geometric figures of them. Four heads peered over his shoulder as he worked silently with his pencil.

"I can make nothing of it," he said after a time.

Again he sat in deep thought, his fellows meanwhile once more examining dollar and disc and the figures their leader had made on the paper.

"Four T's," repeated Captain Hardy after an interval. "Surely that ought to give us a clue."

Once more he studied the penciled disc. Then he turned to the dollar and again examined its markings. He suddenly exclaimed, "Here are four scratches in a straight row." His eyes began to shine. Slowly he turned the coin. "And here are three in another row, like this," and he indicated the positions of the scratches on the paper disc. "You notice that each row runs from the centre of the coin toward the edge. Let's see if there are any more rows."

Very slowly he turned the dollar. "And there are three in a row," he said, indicating the scratches with his pencil, "and here are three more. You notice that the rows all radiate from the centre, like spokes in a wheel. I believe we are getting somewhere, boys."

"'Like spokes in a wheel,'" repeated Roy to himself. "Rows of letters like spokes in a wheel. Four scratches in one row or spoke--these must be the four T's. Three scratches in these other rows must be O's and A's and S's. I've got it! I've got it!" he suddenly shouted. "There must be as many spokes as there are letters in the alphabet."

"I believe you are right, Roy," said Captain Hardy, looking up with a gleam in his eyes. "That's exactly what I am beginning to think. We'll soon see if you are right. Make me another disc."

With a pocket rule he measured the diameter of the dollar. "Practically an inch and a half," he announced, putting down the figures 1.5 on paper. He multiplied those figures by 3.1416.

"That," said he, pointing to the resulting figures, 4.71+, "represents the circumference of a dollar. Now we'll divide the circumference by 26, the number of letters in the alphabet."

He performed the division. "Eighteen one-hundredths of an inch," he announced. "That's practically a scant fifth of an inch. We'll call it so, anyhow," he continued as he marked off the space on a sheet of paper with his rule. "Each sector," he said, "gets exactly that amount of space on the circumference."

He pulled open the drawer of the desk and began to rummage through a tray full of pens, pencils, and other drawing materials. "I wonder if there is such a thing as a pair of dividers here," he remarked. And a moment later he exclaimed "Good!" and drew forth the compasses he was looking for.

He set his dividers according to the space he had marked off with his rule, then proceeded to divide the circumference of the new paper disc. When he had gone completely round the disc, he seized pencil and ruler and began to draw lines from centre to circumference--the spokes of his wheel--each spoke running from the dot in the centre to one of the points indicated by the dividers. When he had finished, the disc was divided into twenty-six equal sectors, like tiny pieces of a pie.

"We shall soon know whether you are right or not in your guess, Roy," said Captain Hardy.

He laid the dollar beside the disc and began to copy on the disc the marks on the dollar. "We'll put four marks in this sector," he said, making four dots with his pencil. "They are like those four scratches here," and he pointed to the four marks in a row on the dollar. "They must be four T's. At any rate we'll call this the T sector. On the dollar you notice this row of three scratches--the next sector to the left of the T sector. You remember we had three O's, three A's, and three S's. These three scratches must, therefore, be O's, A's, or S's. Since they are next to the T's, they are doubtless S's. I'll mark the sector so anyway. That gives us the T sector and the S sector. If we are on the right track, then the sector to the left of the S space is the R sector, and so on. I'll mark the disc that way, anyhow."

Slowly he turned the disc around, putting a letter at the bottom of each sector. When he had finished, he had completed the alphabet. About him clustered his four comrades, too deeply interested to speak. They hardly even breathed.

"Take this paper, Roy," said Captain Hardy, "and tell me how many times each letter in the message appears."

Roy took the paper on which Captain Hardy had made his numerical enumeration. "Three A's," he said.

Captain Hardy made three marks in the A sector.

"No B's, no C's, and two D's."

The D's were scored. So they went through the alphabet. When they were done, the markings on the disc were practically a duplicate of those on the dollar, for Captain Hardy studied the dollar each time before marking the paper disc.

"That's it," cried Willie. "That's it exactly."

"It's right so far as it goes, Willie," said their leader, "but we haven't all of it yet. Suppose I hand you a disc with four T's, three S's, two Z's, three L's, and so on. Could you make a message out of it?"

Willie studied the disc on the desk. "No," he said, "I couldn't. I shouldn't know how to arrange the letters to make words out of them."

"Neither would anybody else," continued Captain Hardy. "Those spies have some way of knowing how to tell the order in which to read these letters."

For some time he sat studying the scratches on the dollar. The four boys were quiet as mice, each trying to solve the problem that stood between them and complete mastery of the cipher.

"You said that the metal disc resembled a spider's web," began Captain Hardy, talking more to himself than to the boys. "We know what the straight lines--the spokes--are for. The concentric circles must be to indicate the order of the letters. Let me see." Again he studied the dollar closely. "Some of these marks are near the centre of the disc, some half-way between centre and circumference, and some close to the outer edge. I believe the secret lies there."

"Listen!" cried Willie of a sudden. "When a spider spins a web, she begins at the centre and works outward. Maybe these spies write their messages in the same way."

"Willie," cried Captain Hardy, "you've hit it exactly. You're as good a reasoner as you are an observer. Now we'll begin at the centre and spin this message outward. What's the first letter?"

"T," said four voices together.

The captain took his dividers and found the scratch nearest the centre of the disc. In the same sector with this scratch were three other scratches in a line.

"It's a T," he announced, "just as it should be."

With his dividers he found the letter next nearest to the centre. It stood alone. "That's a W," he announced.

Rapidly he located the scratch the third nearest to the centre. "And that's an O," he said, looking up with flashing eyes. "We need go no farther. We have the entire secret. We have deciphered their cipher."

A cry of exultation arose.

"To-morrow," continued Captain Hardy, "we will get a piece of transparent celluloid and make a disc like their own. We can ink in the circles and the radius lines and our disc will be almost a duplicate of theirs, except that our disc will be solid while their discs have open spaces between the circles. But that is only a detail. We can read their cipher as well as if we had one of their own discs."

"Wait," cried Willie, as his comrades started to cheer again. "What is the scratch on the milled edge of the dollar for?"

"That," replied Captain Hardy, "is to indicate how the disc is to be placed on the dollar. That scratch is exactly between the Z and the A sectors. It shows where the alphabet begins. Now we have their entire secret."