gun swung its long barrel downward. It sputtered almost
soundlessly--but where it passed, the sand rose up in spouting
fountains.

But his wild speed made the gunfire almost useless. The shell-bursts
were spaced too far apart; they straddled the blot of figures.

He came back at five thousand feet, slowly--until the ship lurched,
and he saw the right wing tip vanish in a shower of molten metal. He
threw the ship over and away from the invisible beam; the plane
writhed and twisted across the last half mile of sky. He was over them
when he pulled into a tight spiral, then he swung the pistol grip that
controlled the gun until the dot in the crystal was merged with the
target of clustering red forms. The gun sputtered.

Below the plane, the quiet desert heaved its smooth surface
convulsively into the air. Even above the roar of the motor Smithy
heard the terrific thunder of that one long explosion.

Above the rim of the forward cockpit Culver's head rolled uneasily;
his voice, thick and uncertain, came back through the phone; and
later--only a matter of minutes later, though fifty miles away--Smithy
set the plane down on a level expanse of sand and tore frantically at
his belt. Colonel Culver was weakly raising his head.

* * * * *

"What hit us?" he demanded when Smithy got to him. "Did I crash?" He
looked about him with dazed eyes from which he never would have seen
again, but for the protection of his goggles.

"Fire," said Smithy tersely. "They did it, the devils, and it wasn't a
flame-thrower, either. There wasn't a flash of their cursed green
light. It just flicked us for a second. You got the worst of it. Your
half roll saved us. That thing, whatever it was, would have ripped our
left wing off in a second."

He was looking at the forward cockpit where the metal fuselage was
melted. The leather cushioning around the edge was black and charred.
Culver's helmet had protected him, but half of his face was seared as
if it had been struck by a white flame.

"But we got some of them: they know we can hit back...." Smithy began,
but knew he was speaking to deaf ears. Again his passenger had lapsed
into unconsciousness.

Quickly he disconnected their own radio receiver and threw on the
emergency radio siren. Ahead of them for a hundred miles an invisible
beam was carrying the discordant blast. Then, with throttle open full,
regardless of levels and of air traffic that tore frenziedl