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fat off their greasy bellies. 'Fuel consumption per man-hour.': Now what in blazes does that mean? Hey, Jim!" He swiveled his chair around to the serried bank of gauge-dials that was Jim Holcomb's especial charge, then sprang to his feet with a startled, "What's the matter?"
The chunky, red-haired control-man was tugging at a lever, his muscles bulging on arms and back, his face white-drawn and tense. "Look!" he grunted, and jerked a grim jaw at one of the dials. The long needle was moving rapidly to the right. "I can't hold the air pressure!"
"Wow, what a leak!" Darl started forward. "How's it below, in the mine?"
"Normal. It's the Dome air that's going!"
"Shoot on the smoke and I'll spot the hole. Quick, man!"
"Okay!"
Thomas' long legs shot him out of the headquarters tent. Just beyond the entrance flap was one of the two gyrocopters used for flying within the Dome. He leaped into the cockpit and drove home the starter-piston. The flier buzzed straight up, shooting for the misted roof.
* * * * *
The Earthman fought to steady his craft against the hurricane wind, while his gray eyes swept the three-mile circle of the vault's base. He paled as he noted the fierce speed with which the white smoke-jets were being torn from the pipe provided for just such emergencies. His glance followed the terrific rush of the vapor. Big as a man's head, a hole glared high up on the Dome's inner surface. Feathered wisps of tell-tale vapor whisked through it at blurring speed.
"God, but the air's going fast," Darl groaned. The accident he had feared through all the months he had captained Earth's outpost on Mercury had come at last. The Dome's shell was pierced! A half-mile high, a mile across its circling base, the great inverted bowl was all that made it possible for man to defy the white hell of Mercury's surface. Outside was an airless vacuum, a waste quivering under the heat of a sun thrice the size it appears from Earth. The silvered exterior of the hemisphere sho