"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 passing 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 passed, 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 passed 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?"