CHAPTER XV

AN UNDERGROUND MYSTERY

“Say, have you fellows heard about that new vacuum tube?” asked Joe, as the boys were tinkering with their set a day or so after the incident of the wildcat.

“What about it?” the others asked, with interest.

“They say it’s the most powerful tube in the world,” Joe continued enthusiastically. “Think of it—this tube is capable of supplying a hundred kilowatts of oscillating high frequency energy to an antenna.”

“Must be some hefty tube,” remarked Bob, rather absently. He was trying to tune in on a station some distance away and there was considerable interference.

“No, that’s just the beauty of it,” said Joe, still on the subject of this wonder tube. “It’s small. Only weighs ten pounds.”

“I suppose that will have a big effect upon radio in general,” said Herb.

“I’ll say so,” Joe returned. “Why, they say that two of these tubes operated in parallel would do the work of a million dollars’ worth of machinery in transatlantic communication.”

“Some tube, all right,” said Jimmy. “I bet it will bring the inventor some hard cash, too.”

“He deserves it,” declared Joe. “Anyone who has brains enough to invent a thing like that ought to be a millionaire.”

“Probably will be, too, before he gets through,” remarked Bob.

Jimmy sighed.

“Oh, for a few brains!” he murmured and Herb grinned happily.

“You said something that time, old timer,” he assured the despondent Jimmy.

However, they wearied even of their radio sets after awhile and decided to take a tramp in the woods, “just to pick up an appetite for dinner.”

“Here’s hoping we don’t pick up a wildcat or two for good measure,” said Joe.

“Oh, I don’t know,” replied Jimmy nonchalantly. “I’ve heard wildcat steaks are very good eating.”

“So are bear steaks,” retorted Joe. “But I’m not particularly anxious to meet the bear.”

“Let’s go over to the ranger station,” suggested Bob, “and see if there’s any news. Then we might go around and see if our cave is still there.”

The boys agreed, and a moment later they were being greeted pleasantly by Mr. Bentley and one or two others. There had been no fires of any account reported, the rangers assured them, and smiled when the boys looked disappointed.

As usual, they stayed at the station longer than they had expected to and when they came out they decided it was too late to go around to their cave that afternoon.

“We’ll make a good early start in the morning and spend the day,” decided Bob. “We can take some canned beans and rolls along so Doughnuts won’t starve to death.”

“That reminds me that we’d better go around by way of the crossroads,” said Herb. “Doughnuts ate up the last bit of jam last night, and if we’re going on a picnic we’ve got to have jam.”

The boys agreed on the necessity, and so started to detour through the woods in the direction of the little crossroads country store, where a few things, they had discovered, could be bought.

But they were destined not to reach the store that afternoon. They had never gone straight from the ranger station to the place, and so the country through which they were passing was new to them.

They knew there was no possibility of their becoming lost, however, for Mr. Bentley told them that if they followed straight along the path they were now on they would come out right at the crossroads.

However, the way was long and as they had been climbing steadily they finally sat down on the crest of a low mountain to regain their breath and look at the scenery.

It was then that Joe discovered, half-way down the mountainside, a curious gaping hole, half concealed by intertwining underbrush.

“Look!” he said. “That looks like a fair-sized cave to me.”

“Let’s go and have a closer look at it,” said Bob, curiously. “It’s probably just a hole, but there may be something interesting about it.”

Jimmy protested, for his short legs were weary, but Herb yanked him to his feet and gave him a shove in the direction of the cave. Jimmy had not been any too securely balanced in the first place, and Herb’s shove had the effect of lifting him completely from his feet. He fell, landed on his side and rolled down the steep side of the mountain, turning over and over and grasping wildly at roots and stones in his path.

So suddenly had it happened that for a moment the other boys only stared. Then, as poor Jimmy went on rolling and finally disappeared in the gaping mouth of the cave they gathered their wits and made after him. Smothering their mirth, they half slid, half fell, down the mountain side.

The ground was rough and stony and they were afraid that Jimmy might be really hurt. Their fears were set at rest, however, when, upon peering into the dark cavern, they found that Jimmy had regained his feet and was glaring with a mixture of sheepishness and rage at Herb.

“You big stiff!” he said, carefully feeling over his pudgy form to make sure there were no bones broken, “next time you feel like shoving a fellow, just look who you’re shoving, will you? I suppose you think this was fun.”

“It was—for us,” retorted Herb, relieved to find he had not seriously hurt his fat chum. “Stop glaring at me, Doughnuts,” he added placatingly. “I didn’t mean to shove so hard, honest I didn’t.”

“Well,” said Jimmy, somewhat mollified, “I suppose I’ll have to take your word for it. Only don’t let it happen again, that’s all.”

“And now that we’re here,” said Bob, gazing about him with lively interest at the walls of the cave into which they had literally stumbled, “what do you say we look around a bit?”

“You bet,” agreed Joe, feeling in his pockets for matches. “From the looks of things, if we’re going to do much exploring we’ll need plenty of light.”

“I’ve got a new box of matches myself,” said Herb. “Any of the rest of you fellows got any?”

It appeared that they all had, and Bob, feeling about on the floor of the cave, found a stick that would serve them admirably as a torch.

This he lighted with one of the precious matches and held it over his head in an attempt to pierce the dark corners of the place.

“Probably ends a few feet farther on,” said Herb, as they carefully made their way forward, groping along the damp walls of the cave. “You go ahead with your light, Bob, and lead the way. It’s as dark as pitch in this hole.”

But, contrary to Herb’s prediction, the cave did not end a few feet further on. As a matter of fact, it seemed to widen as they went forward and the boys began to feel a growing excitement.

“This is getting good,” chortled Bob, then stopped short as by the light of his torch he discovered something new. “Say, fellows,” he cried, in an excited voice, “here’s a tunnel—and, yes, there’s one on the other side.”

“Better and better!” exulted Herb. “Which one of the tunnels shall we explore first?”

“Why not take both?” asked Jimmy, who had completely recovered from his ignominious tumble. “Two of us can go down one of them and the other two can take the other.”

“Nothing doing,” said Bob, firmly. “We’re going to stick together on this jaunt. We don’t want to take any chances of our matches giving out and being left in the dark—not if I know it!”

When Bob spoke in this tone the other boys generally did as he said. And this time was no exception. They tossed coins to determine which of the diverging tunnels they would follow. This proved to be the one to the right of them.

“This piece of stick is burning out,” said Bob, as they turned down the dark passage. “Feel around and see if you can get any more, will you, fellows? If we depend on matches they will be all burnt out before we’ve seen half we want to see.”

They felt about the floor of the cave, which was damp and clammy to the touch, and finally produced a couple of sticks which might be made to do. These last were damp and rotten, but Bob finally succeeded in lighting one.

“We’ll have to work fast, fellows,” he told them. “This isn’t going to last long.”

And so they went ahead in real earnest, thrilled and fascinated by the discovery that there was not one tunnel, or two, in this remarkable cave, but a whole network of them, leading bewilderingly one into another.

In their excitement the Radio Boys temporarily forgot that it was much easier to get in than it would be to find their way out again. All that seemed to matter at the time was to find to what point these fascinating tunnels led. They had been using up matches at an appalling rate of speed.

Then suddenly the torch in Bob’s hand flickered and went out

“More matches,” he called impatiently. “Herb, it’s your turn.”

A minute of dead silence while Herb fumbled wildly in his pockets. Then faintly through the pitch blackness his voice came to them.

“I—haven’t any. I must have lost them.”