Transcriber's Note:
Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.
The Table of Contents is not a part of the original book.


This Ace Science Fiction Book contains the completetext of the original hardcover edition.It has been completely reset in a typefacedesigned for easy reading, and was printedfrom new film.
PRINTING HISTORY
Twayne edition/ 1952
Ace edition/ June 1983
Copyright © 1952 by Twayne Publishers, Inc.
Copyright © renewed 1983 by Charter Communications, Inc.
Introduction © 1952, 1983 by Dr. John D. Clark
New Introduction © 1983 by John F. Carr
Cover art by Gino D'Achille