If a spaceship from another planet should ever visit the earth, no one would be more eager to acknowledge it than our government officials and our scientists. All governments would feel their responsibility to protect the human race if necessary, and to establish diplomatic relations with the alien race if possible. The scientists would want to study, analyze, and try to understand the nature of both the ship and its occupants. Many persons, sincerely believing that flying saucers do exist, berate the investigator who denies their reality and characterize him as stupid, willfully obtuse, or intellectually dishonest because he does not accept the saucer reports at face value but weighs them by the same methods most of us use in weighing evidence in everyday life. When told there’s a horse in the bathtub, for example, the sensible man realizes that the alleged visitation, while not impossible, is extremely improbable. Therefore he does not immediately begin speculating on the color of the horse, where it might have come from, what its purpose may be, and whether it will wreck the bathroom. Instead he adopts the scientific method and first goes to find out whether the horse is really there. Like Fort, some flying-saucer believers are consciously or unconsciously antagonistic to the scientific method and resent its restrictions as a child objects to discipline. Suggesting that a strictly logical approach deprives us of valuable truths about the nature of the universe, and bluntly asserting that present-day physicists and astronomers have closed their minds to the possibility of new knowledge, these enthusiasts imply that we should require less rigorous proof for the reality of saucers than for other types of physical phenomena. Because so many amateur investigators have misunderstood, misrepresented, and condemned the scientists’ attitude, the authors of this book (asking the indulgence of their colleagues) will briefly outline the principles a researcher ordinarily applies to the study of any new problem--the nature of radioactivity, the cause of a disease, or the origin of flying saucers. _The Question of “Evidence”_ Most physicists, chemists, biologists, and astronomers will agree that life in some form probably exists in other parts of the galaxy. These other life forms, if they exist, may or may not have a kind of intelligence similar to our own; if they have, we might or might not be able to recognize it. Such speculations, while fascinating, lie entirely in the realm of theory. They are not facts and do not provide the slightest support to the often stated corollary that intelligent creatures do live on other planets and frequently visit the earth.