PREFACE
This bibliography will indicate to many that the subject of unidentified flying objects
is far broader and more complicated than has been recognized by the adherents to any
one theory or solution. There are deep historical roots, involved social and psycho-
logical implications, and a complex overlapping of many disparate subject fields.
It would seem that the whole must be studied to understand the significance of the
parts, and the phenomenon would seem to be multiple in case and diffuse in source.
There is no simple, single explanation of the UFO phenomenon that can be applied to
all cases described in the literature.
In historical perspective, UFO literature, especially during the last two decades,
indicates a pat~flrn of brief but voluminous "waves." These are made up of books,
magazine artic 1 e1::> and newspaper stories devoted to detailed descriptions of unidentified
flying objects, including controversial acc·:>Unts of people who claim to have had direct
personal experience with these objects and their occupants.
Each new wave of literature is a rediscovery of an old subject, for the tales of
marvelous flying machines piloted by unearthly beings can be traced even beyond their
mention in the ancient Hindu scriptures. Also, it should be noted that the folklore and
mythology of many countries and the legends of many aboriginal tribes seem to be inte-
grally related - - if not completely bound - - to the belief that this planet's skies are
occupied, perhaps even populated, by entities supe!'ior to man.
Thousands of books and pamphlets on the UFO phenomenon have appeared, offering
a wide range of speculation and explanation. Some of these works were first published
in the lSth century. An appreciable wave of "flying saucer" literature appeared in the,
1920' s, simultaneously with astronomers' growing interest in other planets. The most.
popular thesis has always been that the UFOs and theh· occupants are visitors from
another planet or from a distant star system. However, in 1818, some individuals
became convinced that the earth is hollow and that another and alien race occupies its
interior. Since 1944, much material has been published to support this "inner earth"
theory and the hypothesis that UFOs originate there.
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