Page:Popular Science Monthly Volume 73.djvu/146

142 or smaller than the second. The replies are recorded; the ratio of true judgments to the total number of judgments gives the measure of sensibility, and varies directly with it. (3) The Method of Mean Errors—or of Probability of Error. Given a stimulus, the subject is asked to add another just equal to the datum. He deviates more or less; the probable error of the adjustment, in its deviation from the known mean, affords the direct measure of sensibility. The last, so far as an amateur can judge, would seem to be the most important, because the most accurate procedure. As has been said, the resultant generalization holds within limits, upper and lower. But this is just what one anticipates in any law of nature. And there is another, much more pertinent, question. Does the law apply to the relation between sensation and neurosis, or merely to that between neurosis and excitation? If the former, it is psycho-physiological; if the latter, it is no more than physiological or, strictly, physical. Now this raises precisely the fundamental problem: Are sensations measurable? And this, in turn, seems to me to depend upon the possibility of differentiating between sensation and perception (the manner in which we experience sensation). So far as I catch the present drift, the central difficulty remains sub judice. On the other hand, if one be prepared to accept the theory that I call "organicism"—the analogue on the metaphysical side of activism on the ethical, which declares that our whole experience can only be interpreted as a single vast organism, in which every part bears a relation at once of means and end to every other, it follows plainly, in my judgment, that, if not Fechner's law, then some law (possibly not yet known, but necessary all the same) must be operative; and, further, that this law, in certain of its manifestations, is capable of discovery and verification by psycho-physiological methods. You see we must not demand finality from a new science in the first generation of its formal career. At this point the most pitiable errors have been made both by critics and by advocates. The critic who insists that physiological psychology has nothing to tell is in far too big a hurry to judge; and the advocate who urges that physiological psychology can tell everything forthwith deposes his own subject from its hard-earned place as a positive science. It is fair to add, as opposed to my own view, that the greatest American psychologist, Professor James, states (1) that "Fechner's originality consists exclusively in the theoretic interpretation of Weber's law" (p. 545); (2) that "the entire superstructure which Fechner rears upon the facts is not only seen to be arbitrary and subjective, but in the highest