i42 POPULAR SCIENCE MONTHLY 



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. 16 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 excita- 

 tion? If the former, it is psycho-physiological; if the latter, it is no 

 more than physiological or, strictly, physical. Now this raises pre- 

 cisely the fundamental problem: Are sensations measurable? And 

 this, in turn, seems to me to depend upon the possibility of differen- 

 tiating 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 mani- 

 festations, is capable of discovery and verification by psycho-physiolog- 

 ical 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 physi- 

 ological psychology can tell everything forthwith deposes his own sub- 

 ject 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, 17 states (1) that "Fechner's originality consists ex- 

 clusively 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 



lfl Ribot, q. s., p. 1G8; Helmholtz, "Physiol. Optik," pp. 314 f . ; "Hereditary 

 Genius," Galton; and, for a very destructive view, "Introduction to Psycholog- 

 ical Theory," Bowne, pp. 49 ff. See also refs. under Weber's law above. 



17 Cf. " Principles of Psychology," Vol. I., Chap. XIII. 



