Soon they entered the conical top compartment, a room scarcely fifteen feet in diameter, tapering sharply upward to a hollow point some twenty feet above them. The true shape of the room, however, was not immediately apparent, because of the enormous latticed beams and girders which braced the walls in every direction. The air glowed with the violet light of the twelve great ultra-light projectors, like searchlights with three-foot lenses, which lined the wall. The floor beneath their feet was not a level steel platform, but seemed to be composed of many lenticular sections of dull blue alloy. "We are standing upon the upper lookout lenses, aren't we?" asked the girl. "Is that perfectly all right?" "Sure. They're so hard that nothing can scratch them, and of course Roeser's Rays go right through our bodies, or any ordinary substance, like a bullet through a hole in a Swiss cheese. Even those lenses wouldn't deflect them if they weren't solid fields of force." As he spoke, one of the ultra-lights flashed around in a short, quick arc, and the girl saw that instead of the fierce glare she had expected, it emitted only a soft violet light. Nevertheless she dodged involuntarily and Stevens touched her arm reassuringly. "All x, Miss Newton--they're as harmless as mice. They hardly ever have to swing past the vertical, and even if one shines right through you you can look it right in the eye as long as you want to--it can't hurt you a bit." "No ultra-violet at all?" "None whatever. Just a color--one of the many remaining crudities of our ultra-light vision. A lot of good men are studying this thing of direct vision, though, and it won't be long before we have a system that will really work." "I think it's all perfectly wonderful!" she breathed. "Just think of traveling in comfort through empty space, and of actually seeing through seamless steel walls, without even a sign of a window! How can such things be possible?" "I'll have to go pretty well back," he warned, "and any adequate explanation is bound to be fairly deep wading in spots. How technical can you stand it?" "I can go down with you middling deep--I took a lot of general science, and physics through advanced mechanics. Of course, I didn't get into any such highly specialized stuff as sub-electronics or Roeser's Rays, but if you start drowning me, I'll yell."