ing 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 ag