ne command, they darted suddenly toward the ship each
attacked--nearer--then the watchers from a distance saw them disappear,
and the screens back on Earth went suddenly blank.

Half an hour later, nine thousand six hundred and thirty-three titanic
ships moved majestically on.

They swept over Earth in a great line, a line that reached from pole to
pole, and from each the pale green beams reached down, and all life
beneath them was swept out of existence.

* * * *

In Denver, two humans watched the screens that showed the movement of
the death and instant destruction. Ship after ship of the enemy was
falling, as hundreds of the terrestrial machines concentrated all their
enormous energies on its screen of blankness.

"I think, Roal, that this is the end," said Trest.

"The end--of man." Roal's eyes were dreaming again. "But not the end of
evolution. The children of men still live--the machines will go on. Not
of man's flesh, but of a better flesh, a flesh that knows no sickness,
and no decay, a flesh that spends no thousands of years in advancing a
step in its full evolution, but overnight leaps ahead to new heights.
Last night we saw it leap ahead, as it discovered the secret that had
baffled man for seven centuries, and me for one and a half. I have
lived--a century and a half. Surely a good life, and a life a man of six
centuries ago would have called full. We will go now. The beams will
reach us in half an hour."

Silently, the two watched the flickering screens.

Roal turned, as six large machines floated into the room, following F-2.

"Roal--Trest--I was mistaken when I said no screen could stop that beam
of Death. They had the screen, I have found it, too--but too late. These
machines I have made myself. Two lives alone they can protect, for not
even their power is sufficient for more. Perhaps--perhaps they may
fail."

The six machines ranged themselves about the two humans, and a
deep-toned hum came from them. Gradually a cloud of blankness grew--a
cloud, like some smoke that hung about them. Swiftly it intensified.

"The beams will be here in another five minutes," said Trest quietly.

"The screen will be ready in two," answered F-2.

The cloudiness was solidifying, and now strangely it wavered, and
thinned, as it spread out across, and like a growing canopy, it arched
over them. In two minutes it was a solid, black dome that reached over
them and curved down to the groun