of course, merely relative. Then at the moment that our seats
revolved--the thing that made you believe that we had turned about
and were speeding upward--we passed the center of gravity and,
though we did not alter the direction of our progress, yet we were
in reality moving upward--toward the surface of the inner world.
Does not the strange fauna and flora which we have seen convince you
that you are not in the world of your birth? And the horizon--could
it present the strange aspects which we both noted unless we were
indeed standing upon the inside surface of a sphere?"

"But the sun, Perry!" I urged. "How in the world can the sun shine
through five hundred miles of solid crust?"

"It is not the sun of the outer world that we see here. It
is another sun--an entirely different sun--that casts its eternal
noonday effulgence upon the face of the inner world. Look at it
now, David--if you can see it from the doorway of this hut--and
you will see that it is still in the exact center of the heavens.
We have been here for many hours--yet it is still noon.

"And withal it is very simple, David. The earth was once a nebulous
mass. It cooled, and as it cooled it shrank. At length a thin
crust of solid matter formed upon its outer surface--a sort of
shell; but within it was partially molten matter and highly expanded
gases. As it continued to cool, what happened? Centrifugal
force burled the particles of the nebulous center toward the crust
as rapidly as they approached a solid state. You have seen the
same principle practically applied in the modern cream separator.
Presently there was only a small super-heated core of gaseous matter
remaining within a huge vacant interior left by the contraction of