Miscellaneous.—There are many interesting effects due to diffraction of light by edges of objects, by meshes such as a wire screen or a handkerchief, by the eye-media, etc. On looking at a very bright small light-source it may be seen to be surrounded by many colors.
Streamers of light appear to radiate from brilliant sources and all bright areas colored or colorless, when viewed amid dark surroundings, appear to be surrounded by diffuse brushes of light. These brushes are likely to be of a bluish tint.
Many of these phenomena are readily explained, but this cannot be done safely without knowing or recognizing all conditions. Many are not easily explained, especially when reported by others, who may not recognize certain important conditions. For example, authentic observers have reported that black letters on white paper appeared vivid red on a white background, under certain conditions. Of the latter, the apparently important one was “sun’s rays falling aslant the forehead.” When the eyes were shaded with the hand the letters immediately appeared black as they should.
The influence of the color of an object upon its apparent weight is relatively slight, but there is evidence of a tendency to judge a red or black object to be slightly heavier than a yellow or blue object of the same weight. It appears that hue is a minor factor in influencing the judgment and that there is no correlation between the affective quality of a color and its influence upon apparent weight. Although the scanty evidence available attributes but a slight influence to color in this respect, it is of interest in passing as a reminder of the many subtle factors which are at work modifying our judgments.
X
LIGHTING
It should be obvious by this time that the lighting of objects or of a scene can alone produce an illusion, and that it can in still more cases contribute toward an illusion. Furthermore, there are many cases of illusions in lighting due to brightness and color. Many effects of lighting have been described elsewhere with detailed analyses of the underlying principles, but a condensed survey applying particularly to illusions will be presented here.
The comparison of intaglio with low relief has been mentioned several times in preceding chapters. Examples of these as related to lighting are found in [Figs. 70 to 73]. [Fig. 70] represents a bas-relief lighted from above and [Fig. 71] would ordinarily be taken to represent a bas-relief lighted from below. However, the latter was made from a photograph of the mold (intaglio) from which the bas-relief was made and [Fig. 71] really represents an intaglio lighted from above.
Similarly [Fig. 72] represents the bas-relief lighted from the left and [Fig. 73] ordinarily would be taken to be a bas-relief lighted from the right. However, [Fig. 73] was made from a photograph of an intaglio lighted from the left. These amply demonstrate the effect of lighting as an influence upon the appearance of objects and they indicate the importance of correct assumptions in arriving at a correct judgment. In these cases the concealment of the light-source and the commonness of bas-relief as compared with intaglio are the causes for the illusion or the error in judgment. Certainly in these cases the visual sense delivers its data correctly.