PREFACE.

The study of physics, it is true, as well as that of psychology, has been discouraged by influential individuals and sects at various periods under the mistaken impression that the knowledge acquired in this way must ultimately prove harmful to certain other moral or social interests which, in their estimation, ought to be held as most important among mankind. Consequently, the progress of all science has been occasionally much hindered and its cultivation discouraged during almost every period of world history—as if ignorance were productive of the most perfect happiness and most conducive to the interests and well-being of the human species.

These latter notions, however, so far as they relate to physical science, have now been almost entirely discredited. We are now permitted to freely examine the material objects and physical laws of the universe without becoming liable to an accusation of heresy. We believe the same result must ultimately follow in the case of psychological investigation, regarding the presumed tendency of which much prejudice still continues to be held. In this latter department of science, indeed, facts are daily being developed which are not only of great practical importance but also, in other respects, of the highest interest to mankind as social, intelligent, rational, and responsible beings.