darkness for nearly a half-hour, though the green
luminosity far beneath them grew stronger with each passing 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 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.

*