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 a 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?" called Dr. Bird. "Good enough! I was afraid that you might not have kept your gas mask on." "My orders were to keep it on, sir," replied the lieutenant in muffled tones through his mask, "but my mechanician did not obey orders. He passed out cold without any warning about fifteen minutes ago." "Where's your ship?" "Right over here, sir." "We'll take off at once. Your craft is equipped with a Bird silencer?" "Yes, sir."