"Good grief!" exclaimed Tommy. "It's not falling!"

What he said was true, for the stone poised lightly over the opening and drifted like a feather. Then slowly it moved, settling gradually into oblivion. Frank turned the flash downward and they watched in astonishment as the two-pound pebble floated deliberately down the center of the shaft at the rate of not more than one foot in each second.

"Well, I'll be doggoned," breathed Frank admiringly. "Leland has done it. He has conquered gravity. For, in that pit at least, there is no gravity, or at any rate not enough to mention. It has been almost completely counteracted by some force he has discovered and now we know how to follow him down there. Come on Tommy, let's go!"

And, suiting action to his words, Frank jumped into the mouth of the pit where he bobbed about for a moment as if he had jumped into a pool of water. Then slowly he sank from view, and Tommy followed him.

It was a most unique experience, that drop into the heart of the mountain. Practically weightless, the two young men found it quite difficult to negotiate the pa.s.sage. For the first hundred or more feet they continued to b.u.mp about in the narrow shaft and each sustained painful bruises before he learned that the best and simplest method of accommodating himself to the strange condition was to remain absolutely motionless and allow the greatly weakened gravity to take its course. Each movement of an arm or leg was accompanied by a change in direction of movement, and contact with the hard stone walls followed. If they endeavored to push themselves from the contact the result was likely to be an even more serious b.u.mp on the opposite side of the shaft. So they continued the leisurely drop into the unknown depth of the pit.

Frank had turned off the flashlamp, for its battery was giving out and he wished to conserve its remaining energy for eventualities. Thus they were in Stygian darkness for nearly a half-hour, though the green luminosity far beneath them grew stronger with each pa.s.sing minute. It now revealed itself as a clearly defined disc of light that flickered and sputtered continually, frequently lighting the lower end of the shaft with an unusual burst of brilliance. Remotely distant it seemed though, and unconscionably slow in drawing nearer.

"How far do you think we must drop?" called Tommy to Frank, who was probably fifty feet below him in the shaft.

"Well, I figure we have fallen about a thousand feet so far," came the reply, "and my guess is that we are about one third of the way down."

"Then this shaft is over a half-mile deep, you think?"

"Yes, at least a thousand yards, I should say. And I hope his gravity neutralizing machinery doesn't quit all of a sudden and let us down."

"Me, too," called Tommy, who had not thought of that possibility.

This was no joke, this falling into an unknown region so far beneath the surface of good old mother earth, thought Tommy. And how they would ever return was another thing that was not so funny. Frank was always rushing into things like this without counting the possible cost and--well--this might be the last time.

Gradually the mysterious light became stronger and soon they could make out the conformation of the rock walls they were pa.s.sing at such a snail's pace. Layers of vari-colored rock showed here and there, and, at one point there was a stratum of gold-bearing or mica-filled rock that glistened with a million reflections and re-reflections. The air grew warmer and more humid as they neared the mysterious light source. They moved steadily, without acceleration, and Frank estimated the rate at about forty feet a minute. Then, with blinding suddenness, the light was immediately below and they drifted into a tremendous cavern that was illuminated by its glow.

Directly beneath the lower end of the shaft through which they had pa.s.sed, there was a glowing disc of metal about fifteen feet in diameter. They drifted to its surface and sprawled awkwardly where they fell. Scrambling to gain a footing, they bounced and floated about like toy balloons before realizing that it would be necessary to creep slowly from the influence of that repelling force which had made the long drop possible without injury. Gravity met them at the disc's edge with what seemed to be unusual violence.

At first it seemed that their bodies weighed twice the normal amount, but this feeling soon pa.s.sed and they looked about them with incredulous amazement. The metal disc was quite evidently the medium through which the repelling force was set up in the shaft, and to this disc was connected a series of heavy cables that led to a pedestal nearby. On the pedestal was a controlling lever and this moved over a quadrant that was graduated in degrees, one end of the quadrant being labeled "Up" and the other "Down." The lever now stood at a point but a very few degrees from the center or "Zero" mark and on the down side. Frank pulled this lever over to the full "Down" position and they found that they could walk over the disc with normal gravity.

"I suppose," said Frank, "that if the lever is at the other end of the scale one would fall upward with full gravity acceleration--reversed.

At zero, gravity is exactly neutralized, and the intermediate positions are useful in conveying materials or human beings up and down the shaft as desired. Very clever; but what is the reason for it all?"

In the precise center of the great cavern there was a dome or hemisphere of polished metal, and it was from this dome that the eery light emanated. At times, when the light died down, this dome gleamed with dull flickerings that threatened to vanish entirely. Then suddenly it would resume full brilliance, and the sight was marvelous beyond description. A slight hissing sound came from the direction of the dome, and this varied in intensity as did the light.

"Gosh!" said Tommy. "That looks like silver to me. And, if it is, what a wealthy man our friend Leland has become. He has spent his fortune well, even if he used it all to get to this."

"Yes, but where is he?" commented Frank. Then: "Leland! Leland!" he called.

His voice echoed through the huge vault and re-echoed hollowly. But there was no reply save renewed flickerings from the dome.

Leaving the vicinity of the gravity disc, the two men advanced in the direction of the shining dome, which was about a quarter-mile from where they stood. Both perspired freely, for the air was very close and the temperature high. But the light of the dome was as cold as the light of a firefly and they had no hesitancy in drawing near. It was a beautiful sight, this dome of silver with its flickering lights and perfect contour.

"By George, I believe it _is_ silver," exclaimed Frank, when they were within a few feet of the dome. "No other metal has that precise color.

And look! There is a wheelbarrow and some mining tools. Leland has been cutting away some of the material."

Sure enough, there was indisputable evidence of the truth of his statement. And the material was undoubtedly silver!

"Silver Dome," breathed Tommy, holding a lump of the metal in his hand. "A solid dome of pure silver--fifty feet high and a hundred in diameter. How much does that figure in dollars and cents, Frank?"

"Maybe it isn't solid," said Frank dryly, "though it's worth a sizeable fortune even if it is hollow. And we haven't found Leland."

They circled the dome twice and looked into every corner of the great cavern, but there was no sign of the man for whom they searched. The wheelbarrow was half filled with lumps of the heavy metal, and maul and drill lay where they had been dropped by the lone miner. A cavity three feet across, and as many deep, appeared in the side of the dome to show that considerably more than one wheelbarrow load had been removed.

"Funny," grunted Tommy. "Seems almost like the old dome had swallowed him up."

At his words there came the terrific vibration. The light of the dome died out, leaving them in utter darkness, and from its interior there rose the mounting scream that had frightened old Thomas away. From so close by it was hideous, devastating; and the two men clung to each other in fright, expecting momentarily that the earth would give way beneath their feet and precipitate them into some terrible depth from which there could be no return.

Then the sound abruptly ceased and a gleam of light came from under the dome of silver. A crack appeared between its lower edge and the rocky floor of the cavern, and through this crack there shone a light of dazzling brilliancy--a warm light of rosy hue. Wider grew the opening until there was a full three feet between the floor and the bottom of the dome. Impelled by some irresistible force from within, the two men stumbled blindly to the opening, fell to the floor and rolled inside.

There was a heavy thud and the dome had returned to its normal position, with Frank and Tommy prisoners within its s.p.a.cious hollow.

The warm light bathed them with fearful intensity for a moment, then faded to a rosy glow that dulled their senses and quieted their nerves. Morpheus claimed them.

When Frank awoke he found himself between silken covers, and for a moment he gazed thoughtfully at a high arched ceiling that was entirely unfamiliar. Then, remembering, he sprang from the downy bed to his feet. The room, the furnishings, his silken robe, everything was strange. His bed, he saw, was a high one, and the frame was of the same gleaming silver as the dome under which they had been trapped.

The arched ceiling glowed softly with the same rosy hue as had the inner surface of the dome. A large pool of water invited him, the surface of the pool being no more than a foot below the point where it was built into the tile floor of the room. A large open doorway connected with a similar adjoining room, where he suspected Tommy had been taken. On his bare toes, he moved silently to the other room and saw that his guess had been correct. Tommy lay sleeping quietly beneath covers as soft as his own and amidst equal luxury of surroundings.

"Well," he whispered, "this doesn't look as though we would come to any harm. And I might as well take a dive in that pool."

Returning to his own room, he removed the silken garment with which he had been provided and was quietly immersed in the cool, invigorating water of the bath. His head cleared instantly.

"Hi there!" called Tommy from the doorway. "Why didn't you wake me up?

Where are we, anyway?"

With dripping head and shoulders above the water, Frank was compelled to laugh at the sleepy-eyed, wondering expression on the blue-jowled face of his friend. "Thought you were dead to the world," he returned, "you old sleepy-head. And I don't know where we are, excepting that it is somewhere under the silver dome. What's more, I don't much care.

You should get into this water. It's great!"

So saying, he dived to the bottom of the pool and stood on his hands, his feet waving ludicrously above the surface. Tommy sniffed once and then made a quick dash for the pool in his own room. He was not to be outdone by his more energetic partner.

A half-hour later, shaved and attired in their own garments, which had been cleaned and pressed and hung neatly in the closets, they settled themselves for a discussion of the situation. Having tried the doors of both rooms and found them locked from the outside, there was no other course open to them. They must await developments.

"Looks like Leland has quite an establishment down here inside the mountain," ventured Tommy.

"Hm!" snorted Frank, "this place is none of Leland's work. He is probably a prisoner here, as are we. He just stumbled on to the silver dome and was captured by whatever race is living down here beneath it, the same as we were. Who the real inhabitants are, and what the purpose of all this is, remains to be seen."

"You think we are in friendly hands?"