Optical Illusions, Various Other Applications in Architecture

The careful observer will find numberless optical illusions and occasionally he will recognize an attempt on the part of the architect to apply an illusory effect to his advantage. In Fig. 88 some commonplace illusions are presented, not for what they are worth,but to suggest how prevalent they may be.

Fig. 87. - Irradiation in architecture.

Where the pole or column intersects the arches or circle, there is an apparent change in the direction of the curved lines. The different types of arches show different degrees of the optical illusion. It may be of interest for the reader to refer to preceding chapters and to ascertain what types of optical illusions are involved.

If a high wall ends in a series of long horizontal steps at a slightly inclined sidewalk, the steps are not likely to appear horizontal.

Some remarkable optical illusions of depth or of solid form are given to flat surfaces when snow is driven against them so as to adhere in decreasing amounts similar to shading.

A suggestion of augmented height may be given to a low tower by decreasing the size of its successive portions more rapidly than demanded by perspective alone. The same principal can be applied in many ways. For example, in Fig. 89 the roof appears quite extensive when viewed so that the end-walls of the structure are not seen.

Fig. 88. - Some simple geometrical-optical illusions in architecture.

Such optical illusions find applications in the moving-picture studio where extensive interiors, great fortresses, and even villages must be erected within small areas. Incidentally the camera aids to create the illusion of magnitude in photographs because it usually magnifies perspective, thereby causing scenes to appear more extensive in the photographs than in the reality.

Balance in architecture is subject to illusions and might be considered an optical illusion itself. For example, our judgment of balance is based largely upon mechanical laws. A composition must appear to be stable; that is, a large component such as a tower must not be situated too far from what we take as a center of gravity, to appear capable of tipping the remainder of the structure. In physics we would apply the term "moment." Each mass may be multiplied by its distance from the center of gravity, thus determining its moment.

Fig. 89. - By decreasing the exposed length of shingles toward
the top a greater apparent expanse is obtained.

For a building or other composition to appear stable the sum of these moments must be zero; that is, those tending to turn the figure in one direction must be counterbalanced by those tending to turn it in another direction. In appraising a composition, our intellect summates the effects of different parts somewhat in this manner and if satisfactory, balance is considered to have been attained. The colors of the various components exert an influence in this respect, so it is seen that optical illusions may have much to do with the satisfactoriness of architectural compositions.

Various illusions of height, of ceiling, composedness, etc., may be obtained by the color of the ceiling. A dark cornice in an interior may appear to be unsupported if the walls below are light in color, without any apparent vertical supports for the cornice. We are then subjected to the illusion of instability or incongruity. Dark beams of ceilings are not so obtrusive because our intellect tells us that they are supports passing over the top of the walls and are therefore able to support themselves. Color and brightness in such cases are very important.

The architectural details on exteriors evolved under daylighting outdoors so that their form has been determined by the shadows desired. The architect leads his lights and shadows around the building modeling it as he desires. An offset here and a depression there models the exterior in light and shade. The forms must be strong enough to not be lost because of overcast skies but, even with all precautions, the expression of the exterior will vary considerably with natural light. Indoors the architect has a powerful controllable medium in artificial light which he may draw upon for producing various expressions or moods in rooms. The effect of shadows is interesting when viewing some structures flood-lighted at night. In those cases where the light is directed upward there is a reversal of shadows which is sometimes very unsatisfactory.

It is interesting to experiment with various ornamental objects lighted from various directions. For example, a Corinthian capital lighted from below may produce an unpleasant impression upon the observer. We do not like to have the dominant light from below, perhaps because it is annoying to the eyes. Possibly this is an instinct acquired by experience in snow-fields or on the desert, or it may be a heritage of ancestral experience gained under these glaring conditions. This dislike manifests itself when we appraise shadow-effects and therefore our final impression is tempered by it.

All sculptured objects depend for their appearance upon the lighting, and they are greatly influenced by it. In sculpture, in a strict sense, optical illusions play a lesser part than in other arts. Perhaps in those of very large proportions various corrections have been applied. A minor detail of interest is the small cavity in the eye, corresponding to a reversed cornea. This depression catches a shadow which gives considerable expression to the eye.