One of the commonest themes in science fiction is that of parallel universes--a number of nearly identical worlds coexisting in alternate space-time continua. Occasionally, at a vulnerable spot, the barrier between two of these worlds will dissolve so that they overlap near the point of contact. After such an accident a man may find himself unhappily living two lives at once, identical in some ways but so different in others that if one is real, the other cannot be. Until the break is repaired and the incompatible worlds are safely separated once more, the man exists in a state of desperate confusion and performs agonizing mental acrobatics, trying to maintain a foothold in both worlds until he can decide which one is valid. From the “damned” phenomena collected by Charles Fort, plus the legends of Atlantis, Mu, and Lemuria, flying-saucer addicts have constructed a multiplicity of such alternate worlds. Although they differ in minor ways, all are in direct conflict with the real world known to science. Let us ignore, for the moment, the descriptions given by the “contactees” (_Chapter_ X) and consider only the beliefs and/or theories offered by serious proponents of the interplanetary theory and publicized by writers such as Donald E. Keyhoe[I-3, I-4, I-5] Aimé Michel[I-6], and Morris K. Jessup[I-7]. A “Baedeker’s Guide” to saucerdom based solely on statements and speculations in the books published by these investigators would portray a fantastic universe:[A] [A] Following common practice in scientific discussion, we originally included the specific sources of important and/or controversial ideas described in this book and, for maximum accuracy, often used the original phrasing of the several authors involved. In this and certain other sections, however, we have been forced to abandon the more scholarly method of presentation because one author (Major Donald E. Keyhoe) refused permission to quote from his works. “In saucerdom, alien spacecraft continually visit the earth and have done so for centuries. Constructed and controlled by intelligent extraterrestrial beings, the craft perhaps come from secret bases on artificial earth satellites; on the moon; on Mars; on Venus; on Jupiter; perhaps on the planets supposed to be orbiting the binary stars 61 Cygni and 70 Ophiuchi; or from planets supposed to be in orbit around the stars Tau Ceti and Epsilon Eridani, about eleven light-years distant from earth. Radio transmitters serving as beacons for space navigation may exist on both Venus and Jupiter.