" he shouted as he led the way in retreat. "If that is a radite
explosion it will act for several seconds!"

From a safe distance they watched. One corner of the building had been
torn off by the force of the explosion, and as they watched the rest
of the building gradually collapsed and sank into a pile of ruins.

"They had planned on a visit from us all right," said Dr. Bolton
grimly. "They had a surprise for us any way we jumped. If we went in
the front door, that devil's ray was to finish us, and if we went in
the back door the whole place was arranged to blow up as we entered. I
only hope that Stanesky thinks that he has got us all and doesn't
expect an attack on his next base in the morning. If he doesn't, I
think we may give him a rather unpleasant surprise. Of course, that
lamp is smashed into atoms and buried under the debris, but I don't
know what other devil's contraptions that ruin holds. Bolton, have
your men picket it and allow no one near until I get back. I've got to
get to a telephone and get a couple of tanks from Meade and a plane or
two from Langley Field."

* * * * *

Two tanks made their way slowly across country. The front of each tank
was protected by a heavy sheet of vitrilene, while from the turrets of
the tanks projected the wicked looking muzzles of thirty-seven
millimeter guns. Overhead two airplanes from Langley Field soared,
scouting the country. Dr. Bird and Carnes rode in the leading tank.

"It ought to be somewhere near here, unless Karuska lied," said Carnes
as he swept the country with a pair of binoculars.

"He didn't lie," returned Dr. Bird. "It was his subconscious mind
that spoke and it never lies. He spoke of the gun emplacement as being
in a swamp and I have a strong idea that it is submersible. Of course,
it is bound to be well camouflaged, both from land and from air
observation."

The planes circled around again and again, quartering the air like a
pair of well-trained bird dogs will quarter a hunting field. First
high and then low they swooped back and forth, the tanks lumbering
slowly along in the same direction. Presently the occupants of the
leading tank saw one of the planes bank sharply and swing around. It
dropped to an altitude of only a few hundred feet and turned and went
back over the ground it had just crossed.

"I believe that fellow sees something!" exclaimed Carnes.

As he spoke, three green Very lights came from the coc