"Yes, it is force," he smiled. "That's the reason it is almost invisible, from above or below. It is a perpetual sheet of electric force, drawn over the city from end to end. It is so designed and projected, from a ring of stations around the city, that it excludes some vibrations of the ether, and allows others to enter. For instance, it excludes the vibrations called matter, such as air, or such as your car. All of the city's air is pumped in through special vents in the force-shield. On the other hand, it allows the vibrations of light and of radiant heat to enter, and so our city is lighted and heated by the sun itself. Without such a shield, we would be living in a city as bleak and cold as the plains that surround it." "So we crashed into an invisible field of force," I said, and shook my head. "Well, it seemed solid enough when we hit it." "The most powerful force in the world could not crash through it," said Kethra, "and it is fortunate that you were not going at high speed or you would have been annihilated. As it was, we found you both lying unconscious in your car, up on the force-shield, and as we can neutralize it at will, at given spots, we were able to bring you down to the city." "But the car!" I cried. "It is not destroyed, is it? It was not completely smashed?" He shook his head. "It was hardly damaged at all," he assured us. "The point, or prow, was bent back, but that has already been repaired." He paused a moment, then said an astounding thing. "The car does you credit, in its design. It is too bad that, after making it and coming so far into the future, you have been unable to find your friend." I gasped and looked at Lantin. His face reflected utmost surprize, and he said, "I didn't tell him, Wheeler. I'll swear I didn't." Kethra smiled. "Neither of you told me," he said. "But you have lain unconscious for a day, and in that time we learned all your story, my friends, and learned how you came here to warn us of the peril beyond the ice, that peril of an evil being, whom you call the Raider." "But how?" I asked helplessly. In answer, he touched a button set in the wall, and motioned us to seat ourselves in the chairs beside the window. A green-robed servant entered, in a moment, with a metal cabinet. He handed this to Kethra, and then departed. * * * * * The cabinet was an oblong box of black metal, a yard or more in its greatest length. Our companion touched a stud in the floor with his sandaled foot, and a small square section of the floor sprang up on four legs, or supports, forming a little table. Setting the cabinet on this table, our friend opened it.