and silently he ran to the base of the mighty silver towers
nearest him and began to climb the side toward the ravine, where the
maze of girders would hide him, at least partially, from any watchers
back on the plateau. The starlight and the faint weird radiance of the
purple ring above sufficed to guide him.

The cross-braces on the girder he had chosen were spaced closely
enough to serve as the rungs of a ladder. Dan climbed easily, pausing
twice for breath, and to look down at the dark plateau. The vast,
humming machines loomed up strangely in the pale purple light that
fell from the gleaming ring.

Once he looked across toward the other side of the island. The surface
there was more level. He glimpsed tiny moving lights, and huge
stationary masses, apparently as large as ocean liners. He had an
impression of a vast amount of mechanical activity, proceeding in the
darkness very rapidly, and in a silent and orderly fashion.

"The expeditionary force of the Master Intelligence of Mars," he
thought, "preparing to set out against humanity! And what I can do is
the only chance to stop it!"

* * * * *

He climbed again with renewed energy. A few yards more brought him to
the colossal metal ring. Resting upon the three towers, it was a
circular band of shining metal a foot thick and as wide as a road. The
intense purple glow extended several feet from its surface.

Dan touched it tentatively. He felt a tingling electric shock. And he
thought he could feel a radiation coming from it, giving him a curious
sensation of cold. As he reached his hands up and grasped the upper
edge of the great ring, he felt what seemed a physical current of
cold.

Controlling his tendency to shiver, he climbed upon the last brace,
and, lifting his weight with his hands, threw himself face down upon
the flat upper surface of the vast ring. He lay bathed in cold purple
fire. He tingled with the chill of it. A frozen current seemed to
penetrate his body. Involuntarily he trembled, lost his grip and
dangled precariously from the rim.

Only a frantic scrambling restored his hold. Then, fighting the
sensation of freezing cold that came from the mist of purple flame, he
drew himself forward and got to his feet upon the broad surface of the
metal ring. On both sides it curved away like a circular track.
Red-violet fire shimmered about it, bathing him to the waist in a
chilling torrent.

Through coruscating froz