"Our theory is this: the hydrogen atom has been split, resolved into components, not of electrons and the proton centers, but held at some halfway point of decomposition. Matter composed only of neutrons would be heavy beyond belief. This fits the theory in that respect. But the point is this: When these solids are formed--they are dense--they represent in a cubic centimeter possibly a cubic mile of hydrogen gas under normal pressure. That's a guess, but it will give you the idea. "Not compressed, you understand, but all the elements present in other than elemental form for the reconstruction of the atom ... for a million billions of atoms. "Then the light strikes it. These dense solids become instantly a gas--miles of it held in that small space. "There you have it: the gas, the explosion, the entire absence of heat--which is to say, its terrific cold--when it expands." Slim Riley was looking bewildered but game. "Sure, I saw it snow," he affirmed, "so I guess the rest must be O.K. But what are we going to do about it? You say light kills 'em, and fires their bombs. But how can we let light into those big steel shells, or the little ones either?" "Not through those thick walls," said MacGregor. "Not light. One of our anti-aircraft shells made a direct hit. That might not happen again in a million shots. But there are other forms of radiant energy that do penetrate steel...." * * * * * The car had stopped beside a grove of eucalyptus. A barren, sun-baked hillside stretched beyond. MacGregor motioned them to alight. Riley was afire with optimism. "And do you believe it?" he asked eagerly. "Do you believe that we've got 'em licked?" Thurston, too, looked into MacGregor's face: Riley was not the only one who needed encouragement. But the gray eyes were suddenly tired and hopeless. "You ask what I believe," said the scientist slowly. "I believe we are witnessing the end of the world, our world of humans, their struggles, their grave hopes and happiness and aspirations...." He was not looking at them. His gaze was far off in space. "Men will struggle and fight with their puny weapons, but these monsters will win, and they will have their way with us. Then more of them will come. The world, I believe, is doomed...." He straightened his shoulders. "But we can die fighting," he added, and pointed over the hill. "Over there," he said, "in the valley beyond, is a charge of their explosive and a little apparatus of mine. I intend to fire the charge from a distance of three hundred yards. I expect to be safe, perfectly safe. But accidents happen.