But while this fundamental material is constant, it may be given various forms; and both Nature itself and the nature of man may, with increasing knowledge, be increasingly controlled in man's own interests. The railroad, the wireless, and the aeroplane are striking and familiar testimonies to the efficacy of man's informed mastery of the world into which he is born. In the field of physical science, man has, in the short period of three centuries since Francis Bacon sounded the trumpet call to the study of Nature and Newton discovered the laws of motion, magnificently attained and appreciated the power to know exactly what the facts of Nature are, what consequences follow from them, and how they may be applied to enlarge the boundaries of the "empire of man." In his control of human nature, which is in its outlines as fixed and constant as the laws that govern the movements of the stars, man has been much less conscious and deliberate, and more frequently moved by passion and ignorance than by reason and knowledge. Nevertheless, custom and law, the court, the school, and the market have similarly been man's ways of utilizing the original equipment of impulse and desire which Nature has given him. It is hard to believe, but as certain as it is incredible, that the modern professional and businessman, moving freely amid the diverse contacts and complexities pictured in any casual newspaper, in a world of factories and parliaments and aeroplanes, is by nature no different from the superstitious savage hunting precarious food, living in caves, and finding every stranger an enemy. The difference between the civilization of an American city and that of the barbarian tribes of Western Europe thousands of years ago is an accurate index of the extent to which man has succeeded in redirecting and controlling that fundamental human nature which has in its essential structure remained the same through history. Man's ways of association and cooeperation, for the most part, have not been deliberately developed, since men lived and had to live together long before a science of human relations could have been dreamed of. Only to-day are we beginning to have an inkling of the fundamental facts of human nature. But it has become increasingly plain that progress depends not merely on increasing our knowledge and application of the laws which govern man's physical environment. Machinery, factories, and automatic reapers are, after all, only instruments for man's welfare. If man is ever to attain the happiness and rationality of which philosophers and reformers have continually been dreaming, there must also be an understanding of the laws which govern man himself, laws quite as constant as those of physics and chemistry.