Incredible in the concealment of night, the vast protoplasmic pod was doubly so in the glare of day. But it was there before them, not a hundred feet distant. And it boiled in vast tortured convulsions. The clean sunshine struck it, and the mass heaved itself into the air in a nauseous eruption, then fell limply to the earth. * * * * * The yellow membrane turned paler. Once more the staring black eyes formed to turn hopelessly toward the sheltering globe. Then the bulk flattened out on the sand. It was a jellylike mound, through which trembled endless quivering palpitations. The sun struck hot, and before the eyes of the watching, speechless men was a sickening, horrible sight--a festering mass of corruption. The sickening yellow was liquid. It seethed and bubbled with liberated gases; it decomposed to purplish fluid streams. A breath of wind blew in their direction. The stench from the hideous pool was overpowering, unbearable. Their heads swam in the evil breath.... Thurston ripped the gears into reverse, nor stopped until they were far away on the clean sand. The tide was coming in when they returned. Gone was the vile putrescence. The waves were lapping at the base of the gleaming machine. "We'll have to work fast," said MacGregor. "I must know, I must learn." He drew himself up and into the shattered shell. It was of metal, some forty feet across, its framework a maze of latticed struts. The central part was clear. Here in a wide, shallow pan the monster had rested. Below this was tubing, intricate coils, massive, heavy and strong. MacGregor lowered himself upon it, Thurston was beside him. They went down into the dim bowels of the deadly instrument. "Hydrogen," the physicist was stating. "Hydrogen--there's our starting point. A generator, obviously, forming the gas--from what? They couldn't compress it! They couldn't carry it or make it, not the volume that they evolved. But they did it, they did it!" * * * * * Close to the coils a dim light was glowing. It was a pin-point of radiance in the half-darkness about them. The two men bent closer. "See," directed MacGregor, "it strikes on this mirror--bright metal and parabolic. It disperses the light, doesn't concentrate it! Ah! Here is another, and another. This one is bent--broken. They are adjustable. Hm! Micrometer accuracy for reducing the light. The last one could reflect through this slot. It's light that does it, Thurston, it's light that does it!" "Does what?" Thurston had followed the other's analysis of the diffusion process. "The light that would finally reach that slot would be hardly perceptible." "It's the agent," said MacGregor, "the activator--the catalyst! What does it strike upon? I must know--I must!"