DISCRIMINATION AND COMPARISON 495 



Another condition wliicli then favors it is that the sen- 

 sations excited by the differing objects should not come to 

 us simultaneously but fall in immediate succession upon the 

 same organ. It is easier to compare successive than simul- 

 taneous sounds, easier to compare two weights or two tem- 

 peratures by testing one after the other with the same hand, 

 than by using both hands and comparing both at once. 

 Similarly it is easier to discriminate shades of light or color 

 by moving the eye from one to the other, so that they suc- 

 cessively stimulate the same retinal tract. In testing the 

 local discrimination of the skin, by applying compass- 

 points, it is found that they are felt to touch different spots 

 much more readily when set down one after the other than 

 when both are applied at once. In the latter case they 

 may be two or three inches apart on the back, thighs, etc., 

 and still feel as if they were set down in one spot. Finally, 

 in the case of smell and taste it is well-nigh impossible to 

 compare simultaneous impressions at all. The reason why 

 successive impression so much favors the result seems to 

 be that there is a real sensation of difference, aroused by the 

 shock of transition from one perception to another which 

 is unlike the first. This sensation of difference has its own 

 peculiar quality, as difference, wdiich remains sensible, no 

 matter of what sort the terms may be, between which it 

 obtains. It is, in short, one of those transitive feelings, 

 or feelings of relation, of which I treated in a former 

 place (pp. 2'15 if.) ; and, when once aroused, its object 

 lingers in the memory along with the substantive terms 

 which precede and follow, and enables our jvxi.gments of 

 comparison to be made. We shall soon see reason to believe 

 that no two terms can possibly be simultaneously perceived 

 to differ, unless, in a preliminary operation, we have suc- 

 cessively attended to each, and, in so doing, had the transi- 

 tional sensation of difference between them aroused. A 

 field of consciousness, however complex, is never analyzed 

 unless some of its ingredients have changed. We noio 

 discern, 'tis true, a multitude of coexisting things about 

 us at every moment : but this is because we have had a 

 long education, and each thing we now see distinct has 

 been already differentiated from its neighbors by repeated 



