instance, if we heard a fellow’s message and didn’t know where it came from we could tell by turning this back and forth until we got his direction. Then, if we wanted to locate him exactly, we could put it up somewhere else and in that way we could find out just where he was. Frank and I have a particular scheme in hand, but that’s a secret and I’m not ready to tell it yet.”

His mother laughed. “I’m not a bit curious,” she declared. “I suppose some day I’ll wake up to find you two boys have astonished the world.”

But had Frank and Tom told Mrs. Pauling what their secret was she would have been both curious and surprised. Several times within the preceding weeks the boys, listening at their instruments,

had received messages which they could not locate. At first they had given no heed to these, thinking they were merely from some amateur, but when, after repeated requests for the unknown’s call letters, no answer was received and the messages abruptly ceased, the two boys began to be curious.

“There’s something mighty funny about him,” declared Frank. “Every time we answer him or ask a question he shuts up like a clam. Say, Tom, maybe he’s a crook or a bootlegger.”

“More likely some amateur sending without a license and afraid the government inspector will get after him,” suggested Tom. “But I would like to find out who it is.”

A few days later Frank, who was poring over the latest issue of a radio magazine, uttered an exclamation. “Gosh! here’s the scheme,” he cried. “Now we can find out who that mysterious chap is.”

“What’s the big idea?” queried Tom, who was busy making a new vario-coupler.

“Loop aërial,” replied his chum. “Here’s an article all about it. It says they’re used aboard

ships to find the location of other vessels and are called compass aërials.”

Tom dropped his work and hurried to Frank’s side.

“Well,” he remarked, after a few moments’ study of the article and the diagrams, “I don’t see how that would work in our case. It says one ship can find another or can work its way into port by using the loop aërial like a compass, but the trouble is the ship’s moving and so the thing will work, but we can’t go running around New York City or the state with a set in one hand and a big loop aërial in the other.”

“No,” admitted Frank rather regretfully, “but we can tell in which direction his station is.”

“Yes, and it will be fun to make one and experiment with it,” agreed Tom, “especially as the article says the thing cuts out static and interferences and it’s getting on towards warm weather now when the air will be full of static.”

“Well, let’s make one then,” suggested Frank.

As a result, the boys had constructed their loop aërial and a special set to go with it and the very first time they tested the odd affair they were overjoyed

at the result. Again they had picked up the messages which had aroused their curiosity and, by turning the loop one way and then another, they were soon convinced that the sender had a station to the southeast of their own.

“Well, that’s settled,” announced Tom, “and the only things southeast of here are the East Side, the river and Brooklyn. That fellow is not far away—he’s using a very short wave and his messages are strong. I’ll bet he’s right here in New York.”

“I guess you’re right,” agreed Frank, “but that doesn’t do much good. There’s an awful lot of the city southeast from here.”

“Sure there is,” said Tom, “but, after all, what do we care. I still think he’s just some unlicensed chap—probably some kid over on the East Side who can’t pass an examination or get a license and is just having a little fun on the quiet.”

This conversation took place two days before Tom received his father’s message telling of his safe arrival in Cuba and no more messages from the mysterious stranger were heard until the day after Mr. Pauling’s message had been received.

Then, as Tom was listening at the loop aërial

set and idly turned the aërial about, he again picked up the well-known short-wave messages. Heretofore the messages had been meaningless sentences in code, dots and dashes which the boys out of curiosity had jotted down only to find them devoid of any interest—items regarding shipping which Tom had declared had been culled from the daily shipping lists and were being sent merely for practice—and so now, from mere habit, Tom wrote down the letters as they came to him over the instruments. Suddenly he uttered a surprised whistle.

“Gee Whittaker!” he exclaimed in low tones. “Come here, Frank.”

The other hurried to him and as he glanced at the pad on the table beside Tom he too gave an ejaculation of surprise. The letters which Tom had jotted down were as follows: LEAR P IN HAVANA ARRIVED YESTERDAY GET BUSY.

“They are rum runners!” cried Tom as the signals ceased.

“Gosh, I believe they are!” agreed Frank. “But of course,” he added, “it may not mean your father by ‘P’ and we don’t know the first part of

the message. Maybe they were just talking about a ship—that ‘lear’ might have been something about a ship clearing for some place.”

“You are a funny one,” declared Tom. “Here you’ve been insisting all along that there was some deep mystery or plot behind these messages and I’ve said it was just some amateur and nothing to it and now, just as soon as we get a message which really means something, you shift around and say it’s only about some boat.”

“Well, if it’s anything secret why do they talk plain English?” asked Frank. “That’s what makes me change my views. When they were sending things that sounded like nonsense I thought they might be code messages, but now that they send things that are so plain it doesn’t seem mysterious.”

“Yes, there’s sense in that argument, I admit,” replied Tom. “But perhaps there was just as much sense in the others—if they are bootleggers. Of course as you say, they may not mean anything about Dad, but it would be a mighty funny coincidence if any one or anything else beginning with ‘P’ arrived in Havana yesterday and it happened

to come in with this message and with a ‘get busy’ after it. I’ll bet you, Frank, they’re smugglers and that’s a message to some boat or something that the coast’s clear and to unload their stuff. Let’s go down and tell Mr. Henderson about it.”

“No,” Frank advised. “He’d probably laugh at us and it wouldn’t be any use to him anyhow. We’ll keep the message and all others we hear and if anything else is going on we’ll get some more messages, you can bet. And I’ve a scheme, Tom. I know a fellow down at Gramercy Park and we can go down there and set up a loop aërial and see if this chap that’s talking is still southeast of there.”

“That’s a bully scheme!” cried Tom with enthusiasm. “We can turn radio detectives—that’ll be great! And if we find he’s north or west or east of Gramercy Square we can try some other place. Probably your friend knows fellows who have sets all around that part of the city.”

The next day they visited Frank’s friend and after making him promise secrecy they divulged a part of their plan, omitting, at Tom’s suggestion, any reference to their suspicions of the messages

coming from a gang of bootleggers. Henry fell in readily with the idea of locating the messages, which he had also heard repeatedly, and was deeply interested in the loop aërial. He had an excellent set and numerous instruments and supplies and the three boys soon rigged up a compass set in Henry’s home.

“Now, you listen with this and try to pick him up,” instructed Frank. “Keep turning the aërial about in