DISCRIMINATION AND COMPARISON. 5^^1 



ferences, in other words, between diverse pairs of terms, 

 a and h, for example, on the one hand, and c and d on the 

 othei',* can be judged equal or diverse in amount. The dis- 

 tances from one term to another in the series are equal. 

 Linear magnitudes and musical notes are perhaps the im- 

 pressions which we easiest arrange in this way. Next come 

 shades of light or color, which we have little difficulty in 

 arranging by steps of difference of sensibly equal value. 

 Messrs. Plateau and Delboeuf have found it fairly easy to 

 determine what shade of gray will be judged by every one 

 to hit the exact middle between a darker and a lighter 

 shade, t 



How now do we so readily recognize the equality of two 

 differences between different pairs of terms ? or, more 

 briefly, how do we recognize the magnitude of a difference 

 at all '? Prof. Stumj)f discusses this question in an inter- 

 esting way ; % and comes to the conclusion that our feeling 

 for the size of a difference, and our perception that the 

 terms of two diverse pairs are equally or unequally distant 

 from each other, can be explained by no simpler mental 

 process, but, like the shock of difference itself, must be 

 regarded as for the present an unanalyzable endowment 



* The judgment becomes easier if Ihe two couples of terms have one 

 member in comraou, if a — b and b — c, for example, are compared. This, as 

 Stumpf says (Tonpsychologie, i. 131), is probably because the introduction 

 of the fourth term brings involuntary cross- comparisons with it, a and 6 

 with d, b with c, etc., which confuses us by withdrawing our attention 

 from the relations we ought alone to be estimating. 



t J. Delboeuf : l:iements de Psychophysique (Paris, 1883), p. 64. Pla- 

 teau in Stumpf, Tonpsych., i. 125. 1 have noticed a curious enlargement 

 of certain ' distances ' of difference under the influence of chloroform. 

 The jingling of the bells on the horses of a horse-car passing the door, for 

 example, and the rumbling of the vehicle itself, which to our ordinary 

 hearing merge together very readily into a quasi-con\\nvLO\xs, body of 

 sound, have seemed so far apart as to require a sort of mental facing in 

 opposite directions to get from one to the other, as if they belonged in dif- 

 ferent worlds. I am inclined to suspect, from certain data, that the ulti- 

 mate philosophy of difference and likeness will have to be built upon 

 experiences of intoxication, especially by nitrous oxide gas, which lets ?is 

 into intuitions the subtlety whereof is denied to the waking state. Cf. B. 

 P. Blood : The Anaesthetic Revelation, and the Gist of Philosophy (Am- 

 sterdam, N. Y., 1874). Cf. also Mind, vir. 206. 



X Op. cit. p. 126 ff. 



