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.