The victims that were tied in the chair by the savages must have been sitting looking at the audience, so that their backs were to the wall itself. That meant that when the rod was dropped to make contact between the wall and victim, the discharge only burned the sacrifice’s head. Evidence of that was the fact that only skulls were stacked around the altar. The charred head was severed and the body carted outside to one destination or another.
What puzzled Green was how the audience managed to escape the fury of the blast and of the dust, even if they stood at the farthest end of the big room. Determined to find out what happened at those times, he returned to the doorway. Just around its corner, in the second room, he discovered what he’d not noticed before, probably because it was placed so upright and so firmly against one side of the wall. And because its back, which was turned away from the wall, was also made of gray metal. When he switched it around so he could see its other side, he was staring into a mirror about six feet high and four feet wide.
Now he could visualize the ceremony. The victim was strapped into the chair and a rope was tied around the rod. Everybody but the priestess, or whoever conducted the rites, retreated from the altar room. The conductor himself, or herself, then stood in the doorway and released the cord. Before the rod could make contact, the conductor had stepped around the corner. And there the audience saw in the mirror, placed in the doorway so it reflected the interior of the altar room, the ravening discharge of a tremendous electrostatic blast. And immediately afterward, no doubt, they saw nothing because of the dust that would fill the two rooms.
Strange and strong magic to the savages. What myths they must have built about this room, what tales of horrible and powerful gods or demons imprisoned in that wall of dirt! Surely their old women must whisper to the wide-eyed children stories of how the Great Cat-Spirit had been caught by their legendary strong man and savior, some analog to Hercules or Gilgamesh or Thor, and how the Cat-Spirit was the tribe’s to keep prisoner with their magic and to appease from time to time with human kills from other tribes lest it become so angry it burst through the wall of earth and devour everybody upon the floating island!
Green knew that it was hopeless to try to dig through that wall, even if it would be safe for days. It might only be several feet thick, or it might be twenty or more.
But however thick it was, he bet that anybody who had the tools, time and strength to excavate would find, embedded somewhere in that mass, several large dust-collectors. He didn’t know what shape they’d take, because that would depend on the culture that had built them, and their tastes in decorations would differ from Green’s multimillennia-later society. But if they had architectural ideas similar to present-day Terrans they would have constructed the collectors in the shape of busts or of animals’ heads or even of bookcases with false backs of books filling them, books that would in reality have been both chargers and filters. The busts or books would have been pierced with many tiny holes, and through these holes the charged particles of dust would have drifted. Once inside the collectors, they would have been burned.
Looking at the blank dirt before him, Green could see what had happened through the ages. Some part of the burning mechanism had gone wrong – as was the custom of mechanisms everywhere. But the charging effect had continued. And though the dust had piled up around the collectors, the extraordinarily powerful fields had continued to work even through the thick blanket. In the beginning, of course, their field could not have caused any human being harm. But these batteries must have been built to adjust to whatever demand was made of them, though their builders, of course, could have had no idea of how great that demand would some day be. Nevertheless it had come, and the batteries had been equal to it. By the time the savages had found this room they were blocked off by this imposing wall.