"I wouldn't mind being up in a lumber camp myself just now."

"Too early for the country yet," said Jimmy philosophically. "Probably be below zero to-morrow."

"What you thinking about, Bob?" asked Joe, noticing that his chum had been quiet for some time.

"I was thinking," said Bob, coming out of his reverie, "of the difference there has been in generators since the early days of Marconi's spark coil. First we had the spark transmitters and then we graduated to transformers----"

"And they still gave us the spark," added Joe, taking up the theme.

"Then came the rotary spark gap and later the Goldsmith generator----"

"And then," Jimmy continued cheerfully, "the Goldsmith generator was knocked into a c.o.c.ked hat by the Alexanderson generator."

"They'll have an improvement on that before long, too," prophesied Herb.

"They have already," Bob took him up quickly. "Don't you remember what Doctor Dale told us of the new power vacuum tube where one tube can take care of fifty K. W.?"

"Gee," breathed Herb admiringly, "I'll say that's some energy."

"Those same vacuum tubes are being built right now," went on Bob enthusiastically. "They are made of quartz and are much cheaper than the alternators we're using now."

"They are small too, compared to our present-day generators," added Joe.

"You bet!" agreed Bob, adding, as his eyes narrowed dreamily: "All the apparatus seems to be growing smaller these days, anyway. I bet before we fellows are twenty years older, engineers will have done away altogether with large power plants and c.u.mbersome machinery."

"I read the other day," said Joe, "that before long all the apparatus needed, even for transatlantic stations, can be contained in a small room about twenty-five feet by twenty-five."

"But what shall we do for power?" protested Herb. "We'll always have to have generators."

"There isn't any such word as 'always' in radio," returned Bob. "I shouldn't wonder if in the next twenty or thirty years we shall be able, by means of appliances like this new power vacuum tube, to get our power from the ordinary lighting circuit."

"And that would do away entirely with generators," added Joe triumphantly.

"Well, I wouldn't say anything was impossible," said Herb doubtfully.

"But that seems to me like a pretty large order."

"It is a large order," agreed Bob, adding with conviction: "But it isn't too large for radio to fill."

"Speaking of lodging all apparatus in one fair-sized room," Joe went on.

"I don't see why that can't really be done in a few years. Why, they say that this new power vacuum tube which handles fifty K. W. is not any larger than a desk drawer."

"I see the day of the vest-pocket radio set coming nearer and nearer, according to you fellows," announced Herb. "Pretty soon we'll be getting our apparatus so small we'll need a microscope to see it."

"Laugh if you want to," said Bob. "But I bet in the next few years we're going to see greater things done in radio than have been accomplished yet."

"And that's saying something!" exclaimed Joe, with a laugh.

"I guess," said Jimmy thoughtfully, "that there have been more changes in a short time in radio than in any other science."

"I should say so!" Herb took him up. "Look at telephone and telegraph and electric lighting systems. There have been changes in them, of course, but beside the rapid-fire changes of radio, they seem to have been standing still."

"There haven't been any changes to speak of in the electric lighting systems for the last fifteen years or more," said Bob. "And the telephone has stayed just about the same, too."

"There's no doubt about it," said Joe. "Radio has got 'em all beat as far as a field for experiment is concerned. Say," he added fervently, "aren't you glad you weren't born a hundred years ago?"

The boys stopped in at Adam McNulty's cabin to see how the old fellow was getting along. They found him in the best of spirits and, after "listening in" with him for a while and laughing at some of his Irish jokes, they started toward home.

"I wish," said Bob, "that we could have gotten a line on Dan Ca.s.sey. It seems strange that we haven't been able to pick up some real clue in all this time."

For, although the boys had caught several other mysterious messages uttered in the stuttering voice of Dan Ca.s.sey, they had not been able to make head nor tail of them. The lads liked mysteries, but they liked them chiefly for the fun of solving them. And they seemed no nearer to solving this one than they had been in the beginning.

"I know it's a fool idea," said Herb sheepishly. "But since we were the ones that got Ca.s.sey his jail sentence before, I kind of feel as if we were responsible for him."

"It's pretty lucky for us we're not," remarked Joe. "We certainly would be up against it."

On and on the boys went. Presently Joe began to whistle and all joined in until suddenly Jimmy uttered a cry and went down on his face.

"h.e.l.lo, what's wrong?" questioned Bob, leaping to his chum's side.

"Tripped on a tree root," growled Doughnuts, rising slowly. "Gosh! what a spill I had."

"Better look where you are going," suggested Herb.

"I don't see why they can't chop off some of these roots, so it's better walking."

"All right--you come down and do the chopping," returned Joe, lightly.

"Not much! The folks that own the woods can do that."

"Don't find fault, Jimmy. Remember, some of these very roots have furnished us with shinny sticks."

"Well, not the one I tripped over."

It was some time later that the boys noticed that they had tramped further than they had intended. They were on the very outskirts of the town, and before them the heavily-wooded region stretched invitingly.

Jimmy, who, on account of his plumpness, was not as good a hiker as the other boys, was for turning back, but the other three wanted to go on.

And, being three against one, Jimmy had not the shadow of a chance of getting his own way.

It was cool in the shadows of the woods, and the boys were reminded that it was still early in the season. It was good to be in the woods, just the same, and they tramped on for a long way before they finally decided it was time to turn back.

They were just about to turn around when voices on the path ahead of them made them hesitate. As they paused three men came into full view, and the boys stood, staring.

Two of the men they had never seen before, but the other they knew well.

It was the man whose voice they had been trailing all these weeks--Dan Ca.s.sey, the stutterer!

CHAPTER XI