appeared impossible to design a
detonating device which would blow up a bomb before it melted.

The broadcast ended in a matter-of-fact statement that plans for the
defense-system had been given to all the allies of the United States,
that London was already protected and Paris would be within hours, and
that within days the nations which were not allies would be assisted to
establish defenses, so that atomic war need not be feared in the future.

Soames listened with an odd expression on his face.

"That," he said, "started out as a gadget for a castaway to stop arrows
that savages were sniping at him with. I'm very pleased."

There was no more for him to say. The pleasure he felt, of course, would
be the only reward he was likely to get. At the moment he was bent upon
an enterprise his fellow-Americans would have regarded with horror.

* * * * *

Far, far below and surrounded by the blackness of tree-covered ground in
starlight, there was an irregular shape of brightness. It was miles
long. It reflected the stars. It was the flood-control reservoir behind
the Polder Dam. There was no power-plant here. This reservoir merely
took the place of some hundreds of thousands of acres of timbered-off
forest which once had controlled floods more effectively.

Without a word, Soames slanted the 'copter down. Presently it hovered
delicately over the dam's crest and at its very center. It touched. The
rotor ceased to whirl. The motor stopped. There was a great silence.

Fran scrambled down. Soames swung after him. Together, they set up the
device which was a time-transposition unit, with its complicated small
antenna aimed out at the waters of the reservoir.

"I've gambled," said Soames, "that we understand each other. Now you
pull the string."

There was a cord which would discharge the strobe-packs through the
apparatus itself. The discharge would cease with absolute abruptness.
The packs would then recharge themselves from the special batteries
included in the device.

Fran pulled the cord.

There was no noise except a small and inadequate "snap." It seemed that
nothing happened. But there was suddenly a hole in the surface of the
reservoir. It was a large hole.

Something came up out of it. It glittered in ghostly fashion in the
starlight. It rose up and up and up. It was a cylinder with a rounded
top and a diameter of fifty feet or so. It rose and rose, very
deliberately. Then a