SIMULTANEOUS CONTRAST. 



78l 



image which are most prominent in the image itself. What is bright appears 

 larger and overcomes what is dark, while an object, without reference to brightness 

 or colour, has the same relation to its background 

 (fig. 564). When the accommodation is quite 

 accurate, the phenomenon of irradiation is not 



Fig. 564. 

 For irradiation. 



Fig. 565. 

 For irradiation. 



present. [On looking at fig. 585 from a distance, the white squares appear larger 

 and as if they were united by a white band.] 



" A dark object appears smaller than a bright one of the same size. On looking at the same 

 time from a certain distance at two circles of the same size, a white one on a black background, 

 and a black on a white background, we estimate the latter to be about one-fifth less than the 

 former (fig. 564). On making the black circle one-fifth larger they will appear equal. Tycho 

 de Brahe remarks that the moon, when in conjunction (dark), appears to be one-fifth smaller 

 than in opposition (full, bright). The first lunar crescent appears to belong to a larger disc 

 than the dark one adjoining it, which can occasionally be distinguished at the time of the new 

 light. Black clothes make persons appear to be much smaller than light clothes. A light seen 

 behind a margin gives the appearance of a cut in the margin. A ruler, behind which is placed 

 a lighted candle, appears to the observer to have a notch in it. The sun, when rising and 

 setting, appears to make a depression in the horizon" {Goethe). 



[Contrast. The fundamental phenomena are such as these, that a bright object 

 looks brighter surrounded by objects darker than itself ; and darker with surround- 

 ings brighter than itself. There may be contrasts either with bright or dark objects 

 or with coloured ones.] 



Simultaneous Contrast. By this term is meant a phenomenon like the follow- 

 ing : When bright and dark parts are present in a picture at the same time, the 

 bright (white) parts always appear to be more intensely bright the less white there 

 is near them, or, what is the same thing, the darker the surroundings, and, con- 

 versely, they appear less bright the more white tints that are present near them. 

 A similar phenomenon occurs with coloured pictures. A colour in a picture appears 

 to us to be more intense the less of this colour there is in the adjoining parts, that 

 is, the more the surroundings resemble the tints of the contrast colour. Simultane- 

 ous contrast arises from simultaneous impressions occurring in two adjoining and 

 different parts of the retina. 



Examples of Contrast for Bright and Dark. 1. Look at a white network on a black ground ; 

 the parts where the white lines intersect appear darker, because there is least black near them. 



2. Look at a point of a small strip of dark grey paper in front of a dark black background. 

 Push a large piece of white paper between the strip and the background ; the strip on the white 

 ground now appears to be much darker than before. On again removing the white paper, the 

 strip at once again appears bright (Hering). 



3. Look with both eyes towards a greyish -white surface, e.g., the ceiling of a room. After 

 gazing for some time, place in front of the eye a paper tube eight inches long, and an inch to 

 an inch and a quarter in diameter, blackened in the inside. The part of the ceiling seen 

 through the tube appears as a round white spot (Landois). 



Examples for Colours. 1. Place a piece of grey paper on a red, yellow, or blue ground ; the 

 contrast colours appear at once, viz., green, blue, or yellow. The phenomenon is made still 

 more distinct by covering the whole with transparent tracing paper {Herm. Meyer). Under 

 similar circumstances, printed matter on a coloured ground appears in its complementary colour 

 ( W. v. Bezold). 



