was water to come trickling
in. Men came with a roll of cloth that spread open to the shape of a
small boat, while a metal frame expanded within it to hold it taut.

McGuire gasped with dismay as a seaman launched it and leaped heavily
into the frail shell to attach a motor to one end.

"Metal!" the captain reassured him; "woven metal, and water-tight! You
could not pierce it with anything less than a projector."

* * * * *

Sykes was ready with one of the crystal flasks as the boat was brought
alongside, and McGuire followed with another. They took ten of the
harmless-looking containers, and both men held their breaths as the
boat grounded roughly on the boulder-strewn shore.

They lifted them out and bedded them in the sand, then returned to the
submarine. This time Althora, too, stepped into the boat. They loaded
in the balance of the containers; the motor purred. Another landing,
and they stood at last on the island, where a mammoth tube towered
into the sky and the means for its destruction was at their feet.

But there was little time; already the light was dimming, and the time
for the firing of the big weapon was drawing near. The men worked like
mad to carry the flasks to the base of the gun, where a dome of
concrete marked the entrance to the rooms below.

Each man held a flask of the deadly fluid when Althora led the way
where stairs went deep down into the earth under the domed roof. This
part of the work had been foreseen, and the girl held a slender
cylinder that threw a beam of light, intensely bright.

They found a surprising simplicity in the arrangements underground.
Two rooms only had been carved from the solid rock, and one of these
ended in a wall of gray metal that could be only the great base of the
gun. But nowhere was a complication of mechanism that might be damaged
or destroyed, nor any wiring or firing device.

A round door showed sharp edges in the gray metal, but only the
strength of many men could have removed its huge bolts, and these two
knew there must be other doors to seal in the mighty charge.

"Not a wire!" the scientist exclaimed. "How do they fire it?" The
answer came to him with the question.

"Radio, of course; and the receiving set is in the charge itself; the
barrel of the gun is its own antenna. They must fire it from a
distance--back on the island where we were, perhaps. It would need to
be accurately timed."

"Come on!" shouted