McGuire, and raised the flask of explosive to his
shoulder.

* * * * *

Each one knew the need for haste; each waited every moment for the
terrible blast of gun-fire that would jar their bodies to a lifeless
pulp or, by detonating their own explosive, destroy them utterly. But
they carried the flasks again to the top, and the three of them worked
breathlessly to place their whole supply where McGuire directed.

The massive barrel of the gun was beside them; it was held in
tremendous castings of metal that bolted to anchorage in the ground.
One great brace had an overhanging flange; the explosive was placed
beneath it.

Professor Sykes had come prepared. He attached a detonator to one of
the flasks, and while the other two were placing the explosive in
position he fastened two wires to the apparatus with steady but
hurrying fingers; then at full speed he ran with the spool from which
the wires unwound.

McGuire and Althora were behind him, running for the questionable
safety of the sand-hills. Sykes stopped in the shelter of a tiny
valley where winds had heaped the sand.

"Down!" he shouted. "Get down--behind that sand dune, there!"

He dropped beside them, the bared ends of the wires in his hands.
There was a battery, too, a case no larger than his hands. Professor
Sykes, it appeared, had gained some few concessions from his friends,
who had learned to respect him in the field of science.

One breathless moment he waited; then--

"Now!" he whispered, and touched the battery's terminals with the bare
wires.

* * * * *

To McGuire it seemed, in that instant of shattering chaos, that the
great gun itself must have fired. He had known the jar of heavy
artillery at close range; he had had experience with explosives. He
had even been near when a government arsenal had thrown the
countryside into a hell of jarring, ear-splitting pandemonium. But the
concussion that shook the earth under him now was like nothing he had
known.

The hill of sand that sheltered them vanished to sweep in a sheet
above their heads. And the air struck down with terrific weight, then
left them in an airless void that seemed to make their bodies swell
and explode. It rushed back in a whirling gale to sweep showers of
sand and pebbles over the helpless forms of the three who lay battered
and stunned.

An instant that was like an age; then the scientist pointed with a
weak a