r," Ser Perth said impatiently. "The sky itself!"

"Oh--space. We were just getting out there with manned ships. Mostly
vacuum, of course. Of course, we're still in the solar atmosphere, even
there, with the Van Allen belts and such things. Then there are the
stars, like our sun, but much more distant. The planets and the moon--"

"Ignorance was bad enough," Ser Perth interrupted in amazement. He
stared at Dave, shaking his head in disgust. "You obviously come from a
culture of even more superstition than ignorance. Dave Hanson, the sky
is no such thing. Put aside the myths you heard as a child. The sky is a
solid sphere that surrounds Earth. The stars are no more like the sun
than the glow of my cigarette is like a forest fire. They are lights on
the inside of the sphere, moving in patterns of the Star Art, nearer to
us than the hot lands to the south."

"Fort," Dave said. "Charles Fort said that in a book."

Ser Perth shrugged. "Then why make me say it again? This Fort was right.
At least one intelligent man lived in your world, I'm pleased to know.
The sky is a dome holding the sun, the stars and the wandering planets.
The problem is that the dome is cracking like a great, smashed
eggshell."

"What's beyond the dome?"

Ser Perth shuddered slightly. "My greatest wish is that I die before I
learn. In your world, had you discovered that there were such things as
elements? That is, basic substances which in combination produce--"

"Of course," Dave interrupted.

"Good. Then of the four elements--" Dave gulped, but kept silent, "--of
the four elements the universe is built. Some things are composed of a
single element; some of two, some of three. The proportions vary and the
humors and spirits change but all things are composed of the elements.
And only the sky is composed of all four elements--of earth, of water,
of fire and of air--in equal proportions. One part each, lending each
its own essential quality to the mixture, so that the sky is solid as
earth, radiant as fire, formless as water, insubstantial as air. And the
sky is cracking and falling, as you have seen for yourself. The effects
are already being felt. Gamma radiation is flooding through the gaps;
the quick-breeding viruses are mutating through half the world, faster
than the Medical Art can control them, so that millions of us are
sneezing and choking--and dying, too, for lack of antibiotics and proper
care. Air travel is a perilous thing; just tod