it. "I thought these would come in handy. Lucky we had some left over from the blasting we did last week."

He set both cans at the base of the high wall, wired them together, and ran the wire as far as it reached. When the two men were a safe distance away, Mark sparked off the explosive.

There was a thunderous roar: rocks and dirt showered around them, and bits of black powdery stuff. When the smoke cleared, Burl and his father leaped to their feet, rifles in hand.

There was a crack in the side of the wall where the explosive had gone off. And the rip was large enough to get through!

Without a word, they charged across the ground, still smoking from the concussion, and squeezed through the mysterious walls of the enigmatic building.

The walls were thin, thin but hard, as befit masters of atomic engineering. Inside, they found a roomless building—one single chamber within the frame of the outer walls.

A dim, bluish light emanated from the curving ceiling. On the uncleared rocky ground which was the floor of the building were a number of huge machines.

They were spherical glassy inventions, many times the height of a man, connected by strings of thick metal bars and rows of smaller globes, none of which was familiar. There was a steady humming noise, and above, the two giant, metal masts penetrating the ceiling rotated slowly. Doubtless, the great Sun-trapping discs were affixed to the top of these masts.

There was no living thing in sight.

Burl and his father stood silently, half crouched, with rifles at the ready, but nothing moved to challenge them. There was only the humming of the Sun transmitters.

Burl called out, but there was no answer. They advanced cautiously, fearing a trap. The place did not have the look of living things about it. "An automatic station," said Mark under his breath. "I think it's strictly automatic."

It gradually became evident that Mark was right. Everything was automatic. Whoever had built this structure to divert the rays of the Sun had simply set it down, put it in motion, and left. There was no evidence of any provisions for a garrison or a director.

They studied the machines but could make nothing of them. They found what looked like controls, but although they pushed and pulled the levers and knobs, the humming did not cease. It seemed as if the controls were either dummies or had to be specially motivated.

"What do we do now?" asked Burl, after they had tried pulling all the levers on one particular switchboard without any results. "Do you have enough powder left to blow up the machinery?"

His father shook his head. "I had only those two cans with me. We could try shooting into the machinery." Leveling his rifle, he fired at a glassy globe perched upon the central sphere. The bullet pinged off it, and they saw that it had failed even to dent the glistening surface.

"It won't work," said the elder Denning, after several more shots had produced the same result and the concussion reverberating from the enclosed walls had nearly deafened them.

They continued to hunt for a clue, but found none. Dejected, Burl kicked a loose pebble and watched it rattle against a column near the main control board. A small metallic ball rested on top of the column, apparently unattached. A replacement part, he thought to himself, wandering over to it. It was about the level of his head.

With the thought that if he examined it he might learn something of the nature of the working machines, he reached out with both hands to pick it up.

As his hands touched the metallic ball, there was a sudden terrible flash of power. He felt himself grasped by forces beyond his control, paralyzed momentarily like one who has laid hold of an electrically charged wire. He opened his mouth to scream in agony, but he could say nothing. A great force surged through his body, radiating, charging every cell and atom of his being. He felt as if he were being lifted from the floor. Then the globe seemed to dissolve in his hands. It became a glare of light, grew misty, and then vanished.

For a moment he stood there on tiptoe, arced with the potent violence of the force, glowing from within with energies, and then he felt as if the supercharge were dissolving itself, slipping into him, sliding into the ground, then disappearing.

He stood before the column, swaying, but still conscious and alive. His hands were still raised, but there was no ball between them, neither of metal nor of power.

He let them fall to his side and took a step. He was whole, he was sound, he was unharmed. He heard his father's footsteps running to him, and murmured weakly, "I'm all right."

And he was. He could see no sign of damage. "I must have absorbed an awful lot of that energy—or whatever it was," he said.

After resting a moment, he decided to try the useless controls again. Going over to one small board, he idly shoved a lever. This time he felt resistance. The lever was activated. There was a slight change in the radiance of one globe.

"Dad!" Burl shouted. "It works! It works for me now!"

Mark Denning watched as Burl turned dials and levers and got responses. "You must have been charged in a special way," he said excitedly. "That's how they lock their devices. They will only respond to a person carrying that special energy charge, whatever it was. Come on, let's get to the main control, before the effect goes away—if it does."

The two dashed to the panel which, they guessed, activated the main Sun transmitter. Burl grabbed the instruments and threw them back to what seemed to be the zero positions.

The humming rose in intensity, then quieted down and finally stopped. There was a series of clicks, and one by one, the various globes, condensers and glowing machines died out. Above them came a whirring noise, and Burl looked up to see the masts withdrawing into the building, their discs presumably left flat and directionless.

It felt different. Suddenly they knew that the vibrations which had been so heavy in the air about them were gone. There was silence everywhere, the natural silence of an empty, lifeless building in an uninhabited valley.

Burl and his father made their way to the break in the wall and climbed through it.

Outside, the Sun shone down brighter than it had before. The sky was the calm serene blue of a cloudless day. Burl knew that at that same moment, all over the world, the sky was clearer and the Sun warmer.

But for how long? Behind them the building still stood—and its inventors were still to be found.

Chapter 3.
The Secret of A-G 17

The Dennings did not have much time to speculate on the mystery of the Sun-stealers. For just as they were discussing what should be their next course of action, the problem was solved for them. There was a roaring in the air, then a humming, and in a matter of a few more seconds, six rocket helicopters popped into sight, hovered over the valley on streaming jets, and settled down.

"They're U.S. planes!" gasped Burl, jumping to his feet and going to meet them. "It must mean that they know we stopped the machines."

"Obviously," said his father, striding with him to greet the helmeted man who was now stepping out of the lead machine. By this time the last of the squad had landed, and the khaki-clad soldiers in them were already disembarking. "I imagine that all over the world the sky turned a little brighter. It must have been apparent at once."

The leader of the 'copter men reached them. He was a tall, bronzed man, wearing the service coveralls and markings of a captain of the Air Force. He stretched out his hand. "You must be the Dennings. I'm Captain Saunders. I've been asked to bring you back with me right away so that we can get a complete report on this affair. How fast can you get ready?"

"Why," said Burl, "we're ready right now. As soon as we can dump our packs aboard.