tween those two ghastly Elementals . . . what were their names? Swat and Azard. That was it. Something about the progress of experiments in penetrating the curtain between their two spheres, to the point of partial manifestation in the three-dimensional. Working on what they called dead machines; and, now, exulting in the capture of himself, a living machine, with which to work out, guinea-pig fashion, a complete and fixed mastery of First Sphere vibrations, particularly—as he understood the sinister implications—those of Earth's atmosphere.
Penetrating the curtain! . . . His mind went back to the lectures of his graduation days at Solar University, and the post course in astral photism; how each vibrational light world co-existed with those immediately below and above it, so that although they were fused each had its independent practical world. In three-dimensional Terra, for example, you could thrust out an arm into apparent space, yet that arm could actually be penetrating a solidity—say, a battleship sailing on an ocean—in a four dimensional set up. Everything was a matter of vibrations; and the known vibrations on Earth were, to the unknown, as an inch to a mile.
He was not very well up in this sort of thing, but he thought he now knew the answer to some, at least, of the problems surrounding the fantastic stories of flying saucers, unidentified space ships, and so on, which suddenly appeared over Terra and as inexplicably disappeared. Sometimes only fragments of such a machine were seen . . . like an arm thrust through the dividing curtain and then withdrawn. Machines from the Second Sphere, only partly successful in the attempts to manifest in the First Sphere. They were already there, of course; had always been there; but intangible and invisible. Now, by lowering their vibrations, they were becoming both tangible and visible.
He began a feverish examination of the room. Smooth as glass, the walls ran in an unbroken surface. Common sense told him there must be an opening, a door, somewhere, for how, otherwise, had he entered it? How had Zwat and Azard come and gone? He found it by pure accident, when on the verge of despair. His fingernail caught in a depression so cunningly masked that it could have passed for a small flaw in the composition, but was in reality a release contact. An oblong opened. He had no sooner passed through it than, like the automatic door of an elevator, it closed again. He had picked up his space suit on an impulse. The fabric still held, as did that of his clothing; but in both were manifest signs of crumbling. When the struggle between the opposing vibrations was resolved, as it must be, in favor of those of the Second Sphere, the whole substance would probably disappear.
Before him stretched a long cor-
