The methods of psychology are the same as those of other sciences. Science has its beginnings in common knowledge of daily life collected for practical ends. This knowledge is systematized, often in an artificial manner, and facts, often fancies, more remote from daily experience and usefulness are added. Attempts are made to simplify and explain, usually by arbitrary hypotheses. Thus it was thought by the early Greek physicists that the earth is explained by saying that it all consists of water or air or tire. Even in recent times it was thought an explanation to say that water rises in the pump because Nature abhors a vacuum, or that life is explained by the presence of a vital fluid. But as science advances it depends more and more on experiment and measurement. Data are seldom admitted which can not be verified by any competent observer, and mere matters of fact take a subordinate place. Exact science consists almost exclusively of measurements and the relations of quantities.
Psychology until very recently was in the position of science before experiment and measurement had been used. It consisted largely of useless descriptions, artificial classifications, and verbal explanations. A preference was given to matters which are extraordinary and unverifiable. But in the progress of science it has at last become possible to apply experiment and measurement to the mind. We have to-day laboratories of psychology where facts may be discovered, measurements made, and the results verified by every trained student.
To prevent misunderstanding, it may be worth while to notice what is not done in laboratories of psychology. They are not intended for the study of physiology. The functions of the nervous system may throw light on the workings of the mind, but the debt is reciprocal. We know, indeed, more concerning attention, memory, and thought than concerning the cerebral processes which may precede or accompany them. The commonly used term physiological psychology is awkward. There is a science of physiology and a science of psychology, and there are relations between body and mind. But these relations are wider than this—they are between matter and mind. Thus we know that vibrations of a special sort may be accompanied by a sensation which we call blue, but we know almost nothing concerning the corresponding processes in the eye and brain. The, world is one world, and all science is interdependent, but the development of psychology has drawn a sharper line between mental and physical processes than was ever recognized before. The distinctions of material science are comparatively artificial, resting on our ignorance rather than on our knowledge. Whether bodies be as large as planets or as small as atoms is not a matter of great consequence. If we but knew the laws of matter in motion, they would
