qualitative relation, so that, given the antecedent, he can determine the consequent, and vice versa. Now, the point to this is that it is of application wherever such phenomena occur, that for the past and the future they must hold good for the same reason that the multiplication table must hold good. If, however, the student goes not beyond these sciences, he has not learned half his proper lesson. In physics the phenomena are relatively simple. In such sciences as those called natural history the complexity of phenomena becomes very great. Exactitude is not possible to the degree it is in the former studies, and judgments must be formed on different grounds from those. Here there are estimates and probabilities to be considered, and a degree of caution in forming a judgment, not called for in the simpler sciences. There are principles he has got from these physical sciences which he must carry into the more complex studies, viz., that complexity does not impair the certainty that the laws of matter hold true wherever matter is. He is prepared in a good measure to say what can not happen, but not so well prepared to say what may happen. These sciences then act as a check upon hasty deductions; but both of them enforce the idea of continuity, an idea which is very vague in most minds, and is the source of no end of confusion among so-called philosophers.
Again, the science of life contributes to a proper discipline in still other ways. Here one meets with phenomena in which effects are not to be measured by the amount of the acting agent. Consider Koch's consumption-cure: the thousandth of a grain injected into the circulation not only presently brings about great physiological disturbance, but actually locates itself and does its work in diseased tissue in a distant part of the body, yet affects nothing if the body be healthy! Here is a contingent result which is a characteristic of organic phenomena. So to continuity and complexity there is needed a knowledge of contingency in phenomena. By themselves biology and geology, and indeed all the complex sciences, tend to render vague the idea of necessary relations; but when to a knowledge of them is added a knowledge of physics and chemistry, a judgment formed upon an involved question will certainly have much greater weight. Lastly, there is the necessity for a knowledge of psychology. A true understanding of the acts of individuals or communities can not be had without the knowledge of the laws of mind. Every question of a sociologic nature presupposes this as the condition for intelligent action, and it is for the lack of this preparation that all the mistakes in legislation, in schemes for education, for charity, as well as those that men have made in interpreting history, are due.
An adequate knowledge of psychology can not be had without a knowledge of the brain, its functions and relations, and this im-
