The Secret Wireless Part 15

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 circ.u.mference of a dollar. Now we'll divide the circ.u.mference 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 s.p.a.ce on a sheet of paper with his rule. "Each sector," he said, "gets exactly that amount of s.p.a.ce on the circ.u.mference."

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 compa.s.ses he was looking for.

He set his dividers according to the s.p.a.ce he had marked off with his rule, then proceeded to divide the circ.u.mference 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 circ.u.mference--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 s.p.a.ce 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 cl.u.s.tered 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 circ.u.mference, 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 s.p.a.ces 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."

CHAPTER XV

ANOTHER MYSTERY UNRAVELED

A piece of transparent celluloid, furnished by their host from a broken side curtain of his automobile, supplied Captain Hardy with the material needed for making the disc that was to be the key to future communications of the enemy. Carefully he cut the celluloid the size of a dollar, then marked the exact centre of it. Next he clamped the disc on the captured coin. Between the rows of letters he scratched in the straight radius lines--the spokes of a wheel. Then Captain Hardy put the end of one arm of his dividers in the dot at the centre of his disc, and swept the other arm around, scratching a circle just outside the first letter in the message--the innermost T. Examination showed that this circle fell just inside of the second letter in the message--the W. Adjusting his calipers, the draughtsman made a second circle, just outside of this second letter. A third circle fell between the first O and the second T of the message. So Captain Hardy continued, each succeeding circle falling just outside of the succeeding letter in the message. When he had finished, his disc contained twenty-three concentric circles, between which could plainly be seen the bright dots or scratches in the dingy dollar.

"Whew!" said Captain Hardy, as he laid down his dividers. "That's pretty fine work--twenty-three circles within a s.p.a.ce of an inch and a half. I'll wager a watchmaker made their pattern for them. The solid parts of their metal discs can't be much larger than these lines I have scratched on the celluloid. You were right when you named it, Willie.

The parts of it must be just about as thick as a spider-web."

The boys pa.s.sed the dollar and its superimposed disc from hand to hand, examining them with eager interest.

"Suppose they wanted to send a message with more than twenty-four letters in it," said Roy. "How could they do it? I'm sure some of the messages we intercepted had more than twenty-four letters in them."

Captain Hardy picked up the disc-covered dollar and studied it intently. "I suppose," he said after a time, "that they would put more than one dot in the same circle, and the dots would be read in the same way they are now. The one to be read first would be nearest the centre of the coin, and so on. Or they could write on several coins, each coin being numbered in some way, and corresponding to a paragraph in a composition."

Again he studied the dollar closely. "Clever!" he said admiringly.

"Mighty clever! Who would ever dream that those tiny scratches meant anything? Many a time I've seen a dollar scratched and nicked a deal worse than this one is, though they've evidently chosen a battered one so that their own marks will be less noticeable. Why, that coin might have pa.s.sed through our hands a hundred times, and if we had not actually seen it marked we should never dream it said anything other than 'In G.o.d We Trust.' We've had a great stroke of luck, boys."

He paused and meditated. "I wonder if it is luck," he went on. "May not the motto on that dollar explain our good fortune? Perhaps it is Providence rather than blind luck that has guided us. At any rate let us hope so. Now I'm going to report to the Chief. Won't he get a surprise?"

And Captain Hardy left his subordinates, chuckling at the prospect of the Chief's astonishment.

But it was Captain Hardy who had the surprise. Instead of the stern, silent, brusque man he had become accustomed to, Captain Hardy found the Chief smiling and talkative. As his eye fell on Captain Hardy, the Chief rubbed his hands with apparent satisfaction. Evidently something had happened that had put him in an extremely good humor.

"Ah! Captain Hardy," he said, "we beat you to it this time. I already know what you have come to tell me. But I am glad to see you just the same. One of our operators," continued the Chief, "happened to be shifting his tuning-coil when our friends, the enemy, were sending their message yesterday afternoon, so that I have all the latest spy news."

He paused and smiled at his astonished visitor. "You see," he added, a real Irish twinkle coming into his eyes, "the secret service is not so slow after all."