But if such arguments are brought into play, it is evident that it is no longer a legal question, but a psychological one. The psychologist alone deals scientifically with the problem of mutual mental influence and with the reënforcing or awakening of mental energies by social coöperation. He should accordingly investigate the question with his own methods and deal with it from the standpoint of the scientist. This means he is not simply to form an opinion from general vague impressions and to talk about it as about a question of politics, where any man may have his personal idea or fancy, but to discover the facts by definite experiments. The modern student of mental life is accustomed to the methods of the laboratory. He wants to see exact figures by which the essential facts come into sharp relief. But let us understand clearly what such an experiment means. When the psychologist goes to work in his laboratory, his aim is to study those thoughts and emotions and feelings and deeds which move our social world. But his aim is not simply to imitate or to repeat the social scenes of the community. He must simplify them and bring them down to the most elementary situations, in which only the characteristic mental actions are left. Is this not the way in which the experimenters proceed in every field? The physicist or the chemist does not study the great events as they occur in nature on a large scale and with bewildering complexity of conditions, but he brings down every special fact which interests him to a neat, miniature copy on his laboratory table. There he mixes a few chemical solutions in his retorts and his test-tubes, or produces the rays or sparks or currents with his subtle laboratory instruments, and he feels sure that whatever he finds there must hold true everywhere in the gigantic universe. If the waters move in a certain way in the little tank on his table, he knows that they must move according to the same laws in the midst of the ocean. In this spirit the psychologist arranges his experiments too. He does not carry them on in the turmoil of social life, but prepares artificial situations in which the persons will show the laws of mental behaviour. An experiment on memory or attention or imagination or feeling may bring out in a few minutes mental facts which the ordinary observer would discover only if he were to watch the behaviour and life attitudes of the man for years. Everything depends upon the degree with which the characteristic mental states are brought into play under experimental conditions. The great advantage of the experimental method is, here as everywhere, that everything can be varied and changed at will and that the conditions and the effects can be exactly measured.