detailed knowledge. This failure of past methods gives us hope that the principle of sexually intermediate forms may serve as the foundation of a scientific study of character and justifies the attempt to make of it an illuminating principle for the psychology of individual differences. Its application to the science of character, which, so far, has been in the hands of merely literary authors, and is from the scientific point of view an untouched field, is to be greeted more warmly as it is capable of being used quantitatively, so that we venture to estimate the percentage of maleness and femaleness which an individual possesses even in the mental qualities. The answer to this question is not given even if we know the exact anatomical position of an organism on the scale stretching from male to female, although as a matter of fact congruity between bodily and mental sexuality is more common than incongruity. But we must remember what was stated in chap. ii. as to the uneven distribution of sexuality over the body.
The proportion of the male to the female principle in the same human being must not be assumed to be a constant quantity. An important new conclusion must be taken into account, a conclusion which is necessary to the right application of the principle which clears up in a striking fashion earlier psychological work. The fact is that every human being varies or oscillates between the maleness and the femaleness of his constitution. In some cases these oscillations are abnormally large, in other cases so small as to escape observation, but they are always present, and when they are great they may even reveal themselves in the outward aspect of the body. Like the variations in the magnetism of the earth, these sexual oscillations are either regular or irregular. The regular forms are sometimes minute; for instance, many men feel more male at night. The large and regular oscillations correspond to the great divisions of organic life to which attention is only now being directed, and they may throw light upon many puzzling phenomena. The irregular oscillations probably depend chiefly upon the environment, as for instance on
