have heard."

The Dark City occupied a flat plateau, slightly elevated above the
surrounding country, and on the brink of a sheer drop of some six or seven
thousand feet to an arm of the polar sea.

Our problems now were very different from when we had laid siege to the
Lone City. The conformation of the country allowed us no opportunity to
approach closer than two or three miles to the barrage of light we must
expect. We could not reach the city from these nearest points with our
projectors.

There were many lateral ravines depressed below the upper surface of the
main plateau, and though the light-rays from the city, directed
horizontally, would sweep their tops, we found we could traverse many of
them a considerable distance in safety. But from the bottoms of them we
could only fire our rockets without specific aim and our projectors not at
all.

Only by the most fortuitous of circumstances did we escape complete
annihilation the first moment we appeared within range. We had no idea
what lay ahead--although the guides we had brought with us from the Lone
City informed us we were nearing our destination--and the scene remained
in complete darkness until we were hardly more than five miles outside
Tao's stronghold.

Then, without warning, his lights flashed on--not only a vertical barrage,
but a horizontal one as well--sweeping the higher points of the entire
country around for a distance of twelve or fifteen miles.

We were, at the moment, following the bottom of a narrow gully. Had we
been on any of the upper reaches of the plateau we would undoubtedly have
been picked out by one of the roving beams of light and destroyed.

We camped where we were, and again for several days I attempted nothing,
devoting myself to a thorough exploration of the country about us. The
Dark City appeared impregnable. Beams of light from Tao's larger
projectors were constantly roaming about the entire plateau that
surrounded it, and every higher point of vantage from which one of ours
could have reached them must have been struck by their rays a score of
times a day.

It will be understood, of course, that any place where we could mount one
of the higher powered projectors, a task of several hours at best, and
strike the city, must of necessity be also within range of their rays, for
theirs were as powerful as ours. Upon observation I felt convinced that
should we attempt to mount a projector anywhere on these higher points it
w