y attention to it at once. I'll watch for the first
hour."

* * * * *

At the end of an hour Dr. Bird removed his mask with a sigh of relief
and Carnes took his place at the spectroscope. For half an hour he
moved the glass about and then spoke in a guarded tone.

"I don't see any of the lines you told me to look for," he said, "but
in the southwest I get wide band at 310 and two lines at about 520."

Dr. Bird advanced toward the instrument but before he reached it,
Carnes gave an exclamation.

"There they are, Doctor!" he cried.

Dr. Bird sniffed the air. A faint sweetish odor became apparent and he
reached for his gas mask. Slowly his hands drooped and Carnes grasped
him and drew the mask over his face. Dr. Bird rallied slightly and
feebly drew a bottle from his pocket and sniffed it. In another
instant he was shouldering Carnes aside and staring through the
spectroscope. Carnes watched him for an instant and then low whirring
noise attracted his attention and he looked up. Silently he caught
the Doctor's arm in a viselike grip and pointed.

Hovering above the cabin was a silvery globe, faintly luminous in the
moonlight. From its top rose a faint cloud of vapor which circled
around the globe and descended toward the earth. The globe hovered
like a giant humming bird above the cabin and Carnes barely stifled an
exclamation. The door of the cabin opened and Major Trowbridge,
walking stiffly and like a man in a dream, appeared. Slowly he
advanced for ten yards and stood motionless. The globe moved over him
and the bottom unfolded like a lily. Two long arms shot silently down
and grasped the motionless figure and drew him up into the heart of
the globe. The petals refolded, and silently as a dream the globe shot
upward and disappeared.

"Gad! They lost no time!" commented Dr. Bird. "Come on, Carnes, run
for your life, or rather, for Trowbridge's life. No, you idiot, leave
your gas mask on. I'll take the spectroscope; it'll be all we need."

Followed by the panting Carnes, Dr. Bird sped through the night along
an almost invisible path. For half a mile he kept up a headlong pace
until Carnes could feel his heart pounding as though it would burst
his ribs. The pair debouched from the trees into a glade a few acres
in extent and Dr. Bird paused and whistled softly. An answering
whistle came from a few yards away and a figure rose in the darkness
as they approached.

"Maynard?" calle