"Think?" repeated Bob, still wonderingly. "Why, there's only one thing to think, of course. That fool horseshoe of yours, Herb, is one wonderful improvement. I don't know how it works, but it surely is a marvel."

Herb glanced at Jimmy and Joe in triumph.

"What did I tell you?" he said. "Perhaps now you'll believe that my idea wasn't such a fool one after all."

"But what did it do, Bob?" asked Joe, mystified.

"It increased the sensitivity of that old audion tube, that's what it did," replied Bob, absently, his mind already busy with inventive thoughts. "I can't see yet just how it accomplished it, but the connection with the station was certainly clearer and more distinct than usual."

"But how can a magnet increase the sensitivity of a vacuum tube?" asked Jimmy, not yet wholly convinced. "It doesn't make sense."

"Well, I don't see why not," contradicted Joe slowly. "I suppose the improvement is due to the magnetic effect of the magnet upon the electrons flowing from the filament to the plate. I don't exactly see why it should be an improvement, but if it is, then there must be some reason for it."

"I wish we could find the reason!" cried Bob excitedly. "If we could make some improvement upon the vacuum tube----"

"Don't wake him up, he is dreaming!" cried Herb. "If you don't look out, old boy, you'll have us all millionaires."

"Well, there are worse things," retorted Bob, taking the magnet from Herb's hand and placing it near the tube. "This has given us something to think about, anyway."

For a while they puzzled over the mystery, trying to find some way in which the discovery might be made to serve a practical purpose--all except Herb, who retired to one corner of the "lab" to fuss with some chemicals which he fondly hoped might be used in the construction of a battery.

So engrossed were the boys in the problem of the magnet and vacuum tube that they forgot all about Herb and his experiments. So what happened took them completely off their guard.

There was a sudden cry from Herb, followed closely by an explosion that knocked them off their feet. For a moment they lay there, a bit dazed by the shock. Then they scrambled to their feet and looked about them.

Herb, being the nearest to the explosion, had got the worst of it. His face and hands were black and he was shaking a little from the shock. He gazed at the boys sheepishly.

"Wh-what happened?" asked Jimmy dazedly.

"An earthquake, I guess," replied Bob, as he looked about him to see what damage had been done.

Some doughnuts, which their namesake had recently fetched from the store, lay scattered upon the floor, together with some rather dilapidated-looking pieces of candy, but aside from this, nothing seemed to have been damaged seriously.

Jimmy's followed Bob's gaze, and, finding his precious sweets upon the floor, began gathering them up hastily, stuffing a doughnut in his mouth to help him hurry. What mattered it to Jimmy that the floor was none too clean?

"Say, what's the big idea, anyway," Joe demanded of the blackened Herb.

"Trying to start a Fourth of July celebration, or something?"

"I was just mixing some chemicals, and the result was a flare-up,"

explained Herb sulkily. "Now, stop rubbing it into a fellow, will you?

You might know I didn't do it on purpose."

Bob began to laugh.

"Better get in connection with some soap and water, Herb," he said.

"Just now you look like the lead for a minstrel show."

"Never mind, Herb," Joe flung after the disconsolate scientist as he made for the door. "As long as you don't hurt anything but Jimmy's doughnuts, we don't care. You can have as many explosions as you like."

"Humph, that's all right for you," retorted Jimmy. "But I'll have you know I spent my last nickel for those doughnuts."

"Just the same," said Bob soberly, as they returned to the problem of the vacuum tube, "we're mighty lucky to have come off with so little damage. Mixing chemicals is a pretty dangerous business unless you know just what you're doing."

"And even then it is," added Joe.

CHAPTER IX

A HAPPY INSPIRATION

The days pa.s.sed by, the boys becoming more and more engrossed in the fascination of radio all the time. They continued to work on their sets, sometimes with the most gratifying results, at others seeming to make little headway.

But in spite of occasional discouragements they worked on, cheered by the knowledge that they were making steady, if sometimes slow, progress.

There were so many really worth-while improvements being perfected each day that they really found it difficult to keep up with them all.

"Wish we could hear Ca.s.sey's voice again," said Herb, one day when they had tuned in on several more or less interesting personal messages.

"I don't know what good it would do us," grumbled Joe. "If he speaks always in code he could keep us guessing till doomsday."

"He's up to some sort of mischief, anyway," said Bob; "and I, for one, would enjoy catching him at it again."

"We would be more comfortable to have Dan Ca.s.sey in jail, where he belongs," observed Jimmy.

But just at present the trailing of that stuttering voice seemed an impossible feat even for the radio boys. If they could only get some tangible clue to work on!

They saw nothing of Buck Looker or his cronies about town, and concluded that they were still at the lumber camp.

"Can't stay away too long to suit me," Bob said cheerfully.

It was about that time that Bob found out about Adam McNulty. Adam McNulty was the blind father of the washerwoman who served the four families of the boys.

Bob went to the McNulty cabin, buried in the most squalid district of the town, bearing a message from his mother. When he got there he found that Mr. McNulty was the only one at home.

The old fellow, smoking a black pipe in the bare kitchen of the house, seemed so pathetically glad to see some one--or, rather, to hear some one--that Bob yielded to his invitation to sit down and talk to him.

And, someway, even after Bob reached home, he could not shake off the memory of the lonesome old blind man with nothing to do all day long but sit in a chair smoking his pipe, waiting for some chance word from a pa.s.ser-by.

It did not seem fair that he, Bob, should have all the good things of life while that old man should have nothing--nothing, at all.

He spoke to his chums about it, but, though they were sympathetic, they did not see anything they could do.

"We can't give him back his eyesight, you know," said Joe absently, already deep in a new scheme of improvement for the set.

"No," said Bob. "But we might give him something that would do nearly as well."

"What do you mean?" they asked, puzzled.