One night after another performance all of the radio boys were waiting in the railroad station when Larry, who had stepped to the news stand to buy a paper, came hurrying back to where they were sitting.

“I’ve spotted the men who ran me down in the motor boat!” he gasped.  “They’re talking together over in that corner!”

“Are you sure?” asked Bob, as he looked in the direction indicated.

“Dead sure,” declared Larry.  “The look I had at them as the motor boat was making for me is engraved on my memory so that I couldn’t forget it if I wanted to.  Now’s the chance to get those fellows jugged.  You know the police were looking for them after they ran us down and there’s a warrant out for their arrest.  The police didn’t have their names, so the warrant read for John Doe and Richard Roe.  We’ve got to act quickly, as they may get up to take a train at any minute.”

“Keep your eye on them while I get a station policeman,” admonished Bob, as he hurried off.

He found the officer, who listened attentively as he told his story.  Then he walked with Bob toward the men who were still engaged in earnest conversation.

As the officer’s eyes fell upon them, he gave a start.

“That’s Red Pete and Bud McCaffrey, two of the oldest crooks in the business,” he said.  “They’re wanted for more things than that affair of yours.  It will be a feather in my cap if I gather them in.”

He tightened his grip on the club as he came close to the two men.  They looked up at him, and a startled look came into their eyes as they saw his uniform.

“Hello, Pete.  Hello, McCaffrey,” he greeted them.  “I guess you’d better come right along to headquarters.  The Chief would like to have a talk with you.”

With a snarl the men leaped to their feet and sought to get past the officer.  He was too quick for one of them, whom he grabbed by the collar and reduced to submission by two cracks with his club.  The other eluded him, however, and promised to make good his escape.  But quick as a flash Bob thrust out his foot and tripped him, at the same time falling upon him.

The fall knocked the breath out of the fugitive, and Bob had no trouble in holding him until Joe and the other boys came up, together with another policeman, who had been attracted by the fracas.  A patrol wagon was summoned and the prisoners were conveyed to the nearest police station, where they and the bags they had carried were searched in the presence of the boys, who had missed their train in order to be present and give what information they could about the motor boat affair.

The bags were found to contain, among jewelry and other things that were apparently the proceeds of robberies, a number of pawntickets calling for stickpins, watches and other articles which the police lieutenant at the desk announced would be looked up by some of his men.  The prisoners were locked up to await a court examination, and the boys, after having given their names and addresses in case they were wanted later on as witnesses, left for home in a state of high excitement over the stirring events of the night.

Bob kept in touch with the case, and a few days later came rushing up to his friends in high glee.

“What do you think, fellows?” he announced.  “After the extra performance I gave to-day at the broadcasting station, I dropped in at the police station and had a look at some of the loot the police had gathered up on the strength of the pawntickets.  And among them what do you think I saw?”

“The Crown Jewels of England,” guessed Herb.

Bob withered him with a look.

“The stickpins and watches of Buck Looker and Carl Lutz!” announced Bob impressively.  “Their initials were on the watches.”

“Glory be!” cried Larry, who was present.  “That clears me in that matter.  I know none of you fellows believed Buck’s dirty fling, but all the same I’ve felt uncomfortable ever since.”

“Now you’ll get a nice letter of apology from Mr. Buck Looker ­I don’t think,” remarked Joe.

The information was conveyed to Buck and Lutz, and they identified and recovered their property.  But as Joe had predicted, not a word of apology for their unfounded charges was received from either one of the pair.

Not long afterward the arrested men were convicted and sentenced to long prison terms.  It developed that they were old offenders who made a specialty of robbery at summer resorts.

Larry grew steadily better and there was every prospect that his lameness would in time wholly disappear.  But he was doing so well at the broadcasting station that he determined to give up any further idea of vaudeville and devote himself to radio, going to a technical school in the meantime to perfect his education.  Tim steadily advanced in his chosen vocation, and the boys heard from him frequently.  No one rejoiced more than they when they learned that he was at last in the big-time circuit.

During all these events the boys had been busy at developing the receiving set, and at last it was finished to their satisfaction.  In the course of their work they gathered a large amount of familiarity with radio which proved of immense value later on, as will be seen in the next volume of this series, entitled:  “The Radio Boys at Mountain Pass; Or, The Midnight Call For Assistance.”

The special set that represented the advance they had made in radio reception included the regenerative principle.  This feature added immensely to the sensitiveness of the set.  It consisted of a coil, variously known as the tickler, the intensity coil, and the regeneration coil.  It involved three controls, the wave-length tuning, the regenerative coil, and the filament rheostat.  The result of the combination was not only that the radio frequency waves could be carried over into the plate circuit, but that they could be amplified there by the energy derived from the local battery in the plate circuit without change of frequency or wave form, and that they could be fed into the grid circuit, where they increased the potential variations on the grid so that the operation constantly repeated itself.

This “feed-back” regeneration enormously increased the loudness of the receiving signals, and its value to the boys was demonstrated one night when the air was unusually free of static and they clearly heard the signals from Nauen, Germany, and the Eiffel Tower, Paris.  They looked at each other incredulously at first, and then as they heard the signals again too certainly to admit of doubt, they jumped to their feet, clapped each other on the shoulder, and fairly went wild with delight.

“The first boys in this old town to pick up a message from Europe!” cried Joe.  “What next?”

“Asia perhaps,” suggested Jimmy.

“Then Australia,” ventured Herb.

“Or Mars,” predicted Bob.  “Who knows?” he added, as he saw the smile of doubt on his comrades’ faces.  “Marconi thought he might, and he’s no dreamer.  What is impossible to radio?”