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 be 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."
"Well take off at once. Your craft is equipped with a Bird silencer?"
"Yes, sir."
"Come on, Cames, we're going to follow that globe. Take the front cockpit alone, Maynard; Carnes and I will get in the rear pit with the spec and guide you. You can take off your gas mask at an elevation of a thousand feet. You have pack 'chutes, haven't you?"
"In the rear pit. Doctor."
"Put one on, Carnes, and climb in. I've got to get this spec set up before he gets too high."
The Douglass equipped with the Bird silencer, took the air noiselessly and rapidly gained elevation under the urging of the pilot. Dr. Bird clamped the gas-detecting spectroscope on the front of his cockpit and peered through it.
"Southwest, at about a thousand more elevation," he directed.
"Right!" replied the pilot as he turned the nose of his plane in the indicated direction and began to climb. For an hour and a half the plane flew noiselessly through the night.
"Bald Mountain," said the pilot, pointing. "The Canadian Border is only a few miles away."
"If they've crossed the Border, we're sunk," replied the doctor. "The trail leads straight ahead."
FOR a few minutes they continued their flight toward the Canadian Border and then Dr. Bird spoke.
"Swing south," he directed, "and drop a thousand feet and come back."
The pilot executed the maneuver and Dr. Bird peered over the edge of the plane and directed the spectroscope toward the ground.
"Half a mile east," he said, "and drop another thousand. Cames, get ready to jump when I give the word."
"Oh, Lord!" groaned Carnes as he fumbled for the rip cord of his parachute, "suppose this thing doesn't open?"
"They'll slide you between two barn doors for a coffin and bury you that way," said Dr. Bird grimly. "You know your orders, Maynard?"
