the open window into the interior of the dome.

The man, flung against the frame of the window by the shock, uttered a
piercing cry. Before he could recover his stand, or take in what had
happened to him, Dick had gained his feet and leaped upon him. His
right hand closed upon his throat. He bore him to the floor and choked
him into insensibility.

CHAPTER XI

_In the Laboratory_

Not until the man's struggles had ceased, and he lay unconscious,
panting, and blue in the face, did Dick release him. Then he looked
about him.

Save for the workman, he was alone in a rotunda, open to the sky, and,
as he had supposed, the whole upper portion of the dome had been flung
back, leaving an immense aperture into which the sun was shining,
flecking the interior with shafts of light. The temperature, despite
the opening of the dome, must have been in excess of a hundred and
twenty-five degrees.

There was nothing except an immense central shaft, up which ran a
hollow pole of glass, cut off by the invisible paint at the summit of
the dome. The inside of this glass pole was glowing with colored
fires, and it was from this that the intolerable heat came, though its
function Dick could not imagine.

One thing was clear: It was growing hotter each moment. To remain in
that rotunda meant death within a brief period of time.

_And there was no way out!_ Dick glared around him, searching the
glass walls in vain. No semblance of a stairway or ladder, even. Yet
the workman must have entered by some ingress--if only Dick could
discover it!

He began running round the interior of the dome in the brilliant
sunshine, searching frantically for that ingress. And it was growing
hotter! The sweat was pouring down his face beneath the invisible
garment.

Dick was vaguely aware that the silence switch had been thrown in the
room, for his feet made no sound, but the knowledge was latent in his
mind. Two or three times he circumnavigated the interior of the dome,
like a rat in a trap.

Then suddenly he saw a section of the flooring rise in a corner, and a
workman in a blue blouse appear out of the trap door.

* * * * *

He stood there, his face muscles working as he shouted for his
companion, but no sound came from his lips. He looked about him, and
saw the unconscious man beside the window. He started in his
direction.

With a shout, Dick hurled himself toward him. And he checked himself
even as he w