I think I should explain now a little about the physical conformation of Mercury--the "lay of the land," so to speak--in order that the events I am about to describe may be more readily understood. It has already been made clear by Bob Trevor, I believe, that Mercury revolves on its axis only once during the time of its revolution around the sun. Thus, just as a similar condition always makes our moon present very nearly the same face to us, so Mercury presents always the same portion of its surface to the sun.
It will be understood, therefore, that, theoretically, there must be on Mercury but one spot where the sun always is directly overhead. It could not be seen, however, owing to the dense clouds. This spot approximates the center of the region known as the Fire Country.
So far as I could learn, it was here that human life on the planet began. Certainly it was the first region where civilization reached any height. When Columbus was discovering America great cities flourished in the Fire Country--cities of untold wealth and beauty, now fallen into ruins like the great cities of our own Aztec and Inca civilizations.
The Fire Country was then like the equatorial regions of earth--a dense, tropic jungle, hotter than most temperatures we have to bear, but still, by reason of its thick enveloping atmosphere of clouds, capable of supporting life in comparative comfort. Its inhabitants were dark-skinned, but rather more like our Indians than Negroid races.
Then, several centuries ago--the exact time is uncertain, for no written records are kept on Mercury--came the Great Storms. Their cause was unknown--some widespread atmospheric disturbance. These storms temporarily parted the clouds in many places, allowing the direct rays of the sun to fall upon the planet's surface. The resulting temperature destroyed all life, withered all vegetation, with its scorching blast. The inhabitants of the Fire Country were killed by hundreds of thousands, their cities deserted, their land laid a desert waste.
These storms, which it appears began suddenly, have returned periodically ever since, making the region practically uninhabitable. Its surviving races, pushed outward toward the more temperate zone, were living, at this time I am describing, in a much lower state of civilization than the people of the Light Country--a civilization of comparative savagery. In the Light Country they were held as slaves.
This region--thus very aptly known as the Fire Country--embraces a circular area directly underneath the sun. So far as I could learn, it extended outward roughly to those points where--if it had been visible--the sun would have appeared some halfway between zenith and horizon.
Lying outside the circle, in a larger, concentric ring, is the zone known as the Light Country. Entirely free from the equatorial storms, no direct rays of sunlight have ever penetrated its protecting cloud blanket. Here exists the highest state of civilization on the planet.
Beyond the Light Country, in another concentric ring, lies the Twilight Country. It forms a belt about the planet, beginning roughly at those points at which the sun would appear only a short distance above the horizon, and extending back to where the sun would be below the horizon. In this region, as its name implies, there is never more than twilight. It is lightest at the borders of the Light Country, and fades into night at its other side.
Still farther, beyond the twilight zone, lies the region of perpetual night and cold--the Dark Country. This area embraces the rest of the planet, comprising something less than half of its entire surface. Here is eternal night--a night of Stygian darkness, unlighted even by the stars, since the same atmosphere makes them invisible.
The Dark Country, so far as it has been explored--which is very little--is a rocky waste and a sea of solid ice that never melts. Near the borders of the Twilight Country a few people like our Eskimos exist--savages with huge white faces, and great, staring eyes. There are a few fur-bearing animals and birds, but except for this fringe of life the Dark Country is thought to be uninhabited, its terrible cold making life in any form impossible.
So much, in general, for the main geographical features of Mercury. The Great City stands about halfway between the borders of the Fire Country and the edge of the twilight zone. This level marshland, the barren, metallic mountains, and a sort of semitropic jungle, partly inundated by water, comprise nearly all the area of the Light Country.
From the Great City, through the watery jungle, extends a system of little winding bayous--a perfect maze of them, with hundreds of intercommunicating branches--which it would be almost impossible to traverse without losing all sense of direction.
Beyond these bayous, into which their sluggish currents flow, lies the Narrow Sea. On its farther shore begins the Twilight Country, much of it a barren, semifrigid waste, with a little level, tillable land, vast rocky mountain ranges, and a few forests.
In spite of its inhospitable character the Twilight Country is fairly densely populated; and, I realized when I got into it, civilized life is exceedingly difficult to maintain there. I understood then why the Twilight People were so envious of land in the Light Country; and, in truth, I could not blame them for that, or for looking toward our earth with longing.
But just as the Light Country People had defended their borders with implacable determination, so was I determined that they should not invade my world, either. And I was ready to stake my life and even the lives of those I loved here on Mercury in the attempt to prevent them.
