14 P87CH0L0OY. 



fectly steady, slight differences iu shade and color may 

 entirely disappear. If we now tnrn aside the eyes, a nega- 

 tive after-image of the field just fixated at once forms, and 

 mingles its sensations with those which may happen to 

 come from anything else looked at. This influence is dis- 

 tinctly evident only when the first surface has been ' fixated ' 

 without movement of the eyes. It is, however, none the 

 less present at all times, even when the eye wanders from 

 point to point, causing each sensation to be modified more 

 or less by that just previously experienced. On this ac- 

 count successive contrast is almost sure to. be present in 

 cases of simultaneous contrast, and to complicate the 

 phenomena. 



A visual image is modified not only by other sensations just 

 previously experienced, hut also by all those experienced simul- 

 taneously with it, and especially by such as proceed from con- 

 tiguous portions of the retina. This is the phenomenon of 

 simultaneous contrast. In this, as in successive contrast, both 

 brightness and hue are involved. A bright object appears 

 still brighter when its surroundings are darker than itself, 

 and darker when the}' are brighter than itself. Two colors 

 side by side are apparently changed by the admixture, with 

 each, of the complement of the other. And "lastly, a gray 

 surface near a colored one is tinged with the complement 

 of the latter.* 



The phenomena of simultaneous contrast in sight are so 

 complicated by other attendant phenomena that it is ditlfi- 



* These phenomena have close analogues in the phenomena of contrast 

 presented by the temperature-sense (see W. Preyer iu Archiv f. d. ges. 

 Phys., Bd. XXV. p. 79 ff.)- Successive contrast here is shown in the fact 

 that a warm sensation appears warmer if a cold one has just previously 

 been experienced ; and a cold one colder, if the preceding one was warm. 

 If a finger which has been plunged in hot water, and another which has 

 been in cold water, be both immersed in lukewarm water, the same water 

 appears cold to the former finger and warm to the latter. In simultaneous 

 contrast, a sensation of warmth on ajy part of the skin tends to induce the 

 sensation of cold in its immediate neighborhood ; and vice versa. This 

 may be seen if we press with the palm on two metal surfaces of about an 

 inch and a half square and three-fourths inch apart ; the skin between them 

 appears distinctly warmer. So also a small object of exactly the tempera- 

 ture of the palm appears warm if a cold object, and cold if a warm object, 

 touch the skin near it. 



