Part 5 (2/2)

”We may as well go back, boys,” their leader said at last. ”We shall have to depend upon our ears rather than our eyes if we are to catch these villains. But we have made progress. We know where they are.

We have limited our field of observation to one place. Now we shall have to do as we did at Elk City. We shall have to get two portable sets with compact detectors and begin a watch in Hoboken. We'll have to find this hidden wireless by triangulation, just as we caught the dynamiters. But we haven't enough of a force to maintain two watches.

We shall likely have to send for more of the boys to come on.”

They recrossed the river and made their way back to their headquarters.

Lew had heard nothing. He was relieved by Henry.

The others went down to dinner, and food was sent up to the lone watcher. But when his trick was ended, he made the same report that Lew had rendered. He, too, had heard nothing.

”Doubtless,” said Captain Hardy, ”they use their wireless seldom for fear of discovery. Probably they send a message only when troop s.h.i.+ps have actually sailed. That is likely the reason it was such a long time before we caught the first message. And it may be just as long before we hear another. But when it comes, we must be ready with our two detectors. I'll see Chief Flynn about them in the morning. And I'll tell him what we have learned in addition to what the cipher message told us.”

”I wonder,” said Roy, ”how the secret service men ever unraveled that cipher. I could never have done it. I was looking for something like the code message we caught at Camp Brady.”

”It probably was not very difficult, Roy,” replied Captain Hardy, ”or it could not have been fathomed so soon. I believe that most cipher messages to-day are like the one you caught at Camp Brady. Apparently they are innocent messages but they have a hidden meaning. The most difficult cipher messages, I have heard, are of the subst.i.tution kind, where many alphabets are used. It is pretty difficult to decipher such messages unless you have the key word.”

”Then why didn't the Germans use a subst.i.tution cipher when they sent this message about the transports?” asked Willie. ”Then we might never have been able to tell what they said.”

”It was hardly worth while, Willie. They know the authorities are listening for their messages. It made no particular difference if the contents of this message were known. But when they send out an order for a spy to do something, I have no doubt they use the most difficult code they can devise, or at least one that they believe only the spy will understand. So we may expect to catch messages in different codes before we are through with our work.”

Captain Hardy rose and began to look along the shelves of books. ”Here is a volume,” he said presently, ”that will tell us a great deal about cipher messages.”

He had just laid open the book when Roy rushed in from the wireless room. ”I've got another message,” he said, holding out a paper on which was a long string of letters.

”I wasn't expecting another message so soon,” said Captain Hardy in surprise. Slowly he read the letters on the paper Roy had given him:

”FTSt.i.tEIAFTDLLTNSYWTORPSLHVNRLEEYLIOTEIH UAOSEIEGGEVNCENDRRTERNRADSNLEEITOCGEOSHM.”

”It looks like the same cipher used before,” he went on. ”If it is, we can unravel this message without bothering the secret service. At any rate we'll make a try at it. Where's that other message, Willie?”

The first message was brought. Captain Hardy spread it on the table and the group bent over it.

”The letters divide evenly into four lines, you notice,” said the leader. ”Let's see if this message will do the same.”

He counted the letters with his pencil. ”Eighty,” he announced. ”That would make four lines of twenty letters each. We'll try it.”

Rapidly he copied the first twenty letters. Below them he made a second line of the next twenty letters. Then the third set of twenty was written down. As he began the fourth row the three boys at his side held their breath.

”He's got it,” Willie Brown cried, as Captain Hardy wrote down the first letter. ”He's got it. It spells four.”

Rapidly Captain Hardy finished out his line. The letters he had written down read like this:

FTSt.i.tEIAFTDLLTNSYWT ORPSLHVNRLEEYLIOTEIH UAOSEIEGGEVNCENDRRTE RNRADSNLEEITOCGEOSHM

He picked up the paper and slowly spelled out the following message:

”Four--transports--sailed--this--evening-- Large--fleet--evidently--collecting-- No--destroyers--with--them.”

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