Silently, with catlike tread, they inched their way forward flat against the wall, keeping out of the blue flood of illumination. The shapes, or rather segments of shapes within, moved about, engrossed in the business at hand, unaware of the creeping death. The Earthmen had reached their stations unobserved, one on either side of the open slide. Very carefully Hilary protruded his head around the vita-crystal, and ducked back almost instantly. But his quick eye had taken in all the essential details in that momentary vision. There were about a dozen Mercutians in the long laboratory, and each had a sun-tube dangling from his belt, ready at hand. The laboratory was crowded with apparatus, but what had drawn Hilary's attention was a gigantic gleaming metallic sphere set up prominently in the center of the room. Protruding from it at all angles were great quartz tubes, through which a blue light pulsed and flamed. It was connected by huge cables to a spark-bathed dynamo. Other cables writhed through the translucent ceiling. The weather machine! Hilary took a firmer grip on his automatic, nodded once to Grim. The two Earthmen stepped simultaneously through the open door. "Raise your paws high and keep them up." Hilary's voice cracked like a whip through the busy confusion of the laboratory. The Mercutians, scattered as they were, whirled around from their tasks to face two deadly weapons held by two determined-looking men. There was a chorus of strange guttural oaths, but every hand moved skyward, reluctantly. * * * * * Hilary picked out the most blasphemous sounding of the cursers, rightly deeming him the Cor in charge. "You," he said, "what switches regulate the weather machine?" The Mercutian Cor was a particularly ugly specimen. The gray warts were gigantic, hiding whatever semblance of manlike features there might have been beneath. "I'll see you dogs burned to a cinder in the sun first," he growled. "Keep them covered, Grim," Hilary said sharply. "I'll take care of this fellow personally." He walked straight across the room for the Cor, eyes blazing, index finger on trigger. The Cor, fear staring out of his lidless eyes, backed slowly away from the approaching death. There was a hushed silence. "I'll tell, I'll tell!" the Cor screamed, as the relentless weapon almost touched his paunchy stomach. "I thought you would," Hilary said grimly, not for an instant relaxing the pressure against the trigger. "If you value your worthless hide, you'd better talk, and talk fast. What switch reverses the machine, to bring on rain? If you are wise, you won't try to fool me." The wretch almost stumbled in his eagerness. "By the gray soil of Mercury I'll tell you the truth." His arm flung up, pointing. "That knob over there controls the--"