emed madly
gyrating beneath them; Mercury was a line of light, as it swirled about
the swiftly moving sun.

But that thirty thousand years was thirty days to the men of the ship.
Their time rate immensely retarded, they worked on their calculations.
At the end of that month Arcot had, with the help of Morey and Wade,
worked out the last of the formulas of artificial matter, and the
machines had turned out the last graphical function of the last branch
of research that they could discover. It was a time of labor for them,
and they worked almost constantly, stopping occasionally for a game of
some sort to relax the nervous tension.

At the end of that month they decided that they would go to Earth.

They speeded their time rate now, and flashed toward Earth at enormous
speed that brought them within the atmosphere in minutes. They had
landed in the valley of the Nile. Arcot had suggested this as a means of
determining the advancement of life of man. Man had evidently
established some of his earliest civilizations in this valley where
water and sun for his food plants were assured.

"Look--there _are_ men here!" exclaimed Wade. Indeed, below them were
villages, of crude huts made of timber and stone and mud. Rubble work
walls, for they needed little shelter here, and the people were but
savages.

"Shall we land?" asked Arcot, his voice a bit unsteady with suppressed
excitement.

"Of course!" replied Morey without turning from his station at the
window. Below them now, less than half a mile down on the patchwork of
the Nile valley, men were standing, staring up, collecting in little
groups, gesticulating toward the strange thing that had materialized in
the air above them.

"Does every one agree that we land?" asked Arcot.

There were no dissenting voices, and the ship sank gently toward a road
below and to the left. A little knot of watchers broke, and they fled in
terror as the great machine approached, crying out to their friends,
casting affrighted glances at the huge, shining monster behind them.

Without a jar the mighty weight of the ship touched the soil of its
native planet, touched it fifty millenniums before it was made, five
hundred centuries before it left!

Arcot's brow furrowed. "There is one thing puzzles me--I can't see how
we can come back. Don't you see, Morey, we have disturbed the lives of
those people. We have affected history. This must be written into the
history that exists.

"This se