Part 18

Incidentally on viewing some picture frames in which the grain of the wood was noticeable, the frames did not appear to be strictly rectangular. The illusions were so strong that only by measuring the frames could one be convinced that they were truly rectangular and possessed straight sides. Two of these are represented in Figs. 82 and 83. In the former, the horizontal sides appear bent upward in the middle and the two vertical sides appear bowed toward the right. In Fig. 83, the frame appears considerably narrower at the left end than at the right. Both these frames were represented in the original drawings by true rectangles.

Many illusions are to be seen in furniture and in other woodwork in which the grain is conspicuous. This appears to the author to be an objection in general to this kind of finish. In Fig. 84 there is reproduced a photograph of the end of a board which was plane or straight notwithstanding its warped, or bowed, appearance. The original photographs were placed so as to be related as shown in the figure. Various degrees of the illusion are evident. The reader will perhaps find it necessary to convince himself of the straightness of the horizontal edges by applying a straight edge. These are examples of the same illusion as shown in Figs. 37 to 40.

Perhaps a brief statement regarding the modern isms in art may be of interest. In considering some of the extreme examples, we must revise our idea that art is or should be always beautiful. The many definitions of art would lead us too far afield to discuss them here but in its most extended and popular sense, art may be considered to mean everything which we distinguish from nature. Certainly art need not be beautiful, although it does seem that the world would welcome the beautiful and would get along contentedly without art that is ugly or repulsive. The modern isms must be viewed with consideration, for there are many impostors concealing their inabilities by flocking to these less understood fields. However, there are many sincere workers--research artists--in the modern isms and their works may best be described at present as experiments in the psychology of light, shade, and color. They have cast aside or reduced in importance some of the more familiar components such as realism and are striving more deeply to utilize the psychology of light and color. Some of them admit that they strive to paint through child's eyes and mind--free from experience, prejudice, and imitation. These need all the scientific knowledge which is available--and maybe more.

In closing this chapter, it appears necessary to remind the artist and others that it is far from the author's intention to subordinate the artist's sensibility to the scientific facts or tools. Art cannot be manufactured by means of formulae. This would not be true if we knew a great deal more than we do pertaining to the science of light, color, and vision. The artist's fine sensibility will always be the dominating necessity in the production of art. He must possess the ability to compose exquisitely; he must be able to look at nature through a special temperament; he must be gifted in eye and in hand; he must be master of unusual visual and intellectual processes. But knowledge will aid him as well as those in other activities. A superior acquaintance with scientific facts lifted past masters above their fellows and what helped Leonardo da Vinci, Rembrandt, Velasquez, Turner, Claude, Monet, and other masters will help artists of today. What would not those past masters have accomplished if they had available in their time the greater knowledge of the present!

XIII

ARCHITECTURE

Many illusions are found in architecture and, strangely enough, many of these were recognized long before painting developed beyond its primitive stages. The architecture of classic Greece displays a highly developed knowledge of many geometrical illusions and the architects of those far-off centuries carefully worked out details for counteracting them. Drawings reveal many illusions to the architect, but many are not predicted by them. The ever-changing relations of lines and forms in architecture as we vary our viewpoint introduce many illusions which may appear and disappear. No view of a group of buildings or of the components of a single structure can be free from optical illusions. We never see in the reality the same relations of lines, forms, colors, and brightnesses as indicated by the drawings or blue-prints. Perhaps this is one of the best reasons for justifying the construction of expensive models of our more pretentious structures.

No detailed account of the many architectural illusions will be attempted, for it is easy for the reader to see many of the possibilities suggested by preceding chapters. However, a few will be touched upon to reveal the magnitude of the illusory effect and to aid the observer in looking for or recognizing them, or purely for historical interest. In architecture the eye cannot be wholly satisfied by such tools as the level, the square, and the plumb-line. The eye is satisfied only when the appearance is satisfactory. For the purpose of showing the extent of certain architectural illusions, the compensatory measures applied by the Greeks are excellent examples. These also reveal the remarkable application of science to architecture as compared with the scanty application in painting of the same period.

During the best period of Grecian art many refinements were applied in order to correct optical illusions. It would be interesting to know to what extent the magnitude of the illusions as they appeared to many persons were actually studied. The Parthenon of Athens affords an excellent example of the magnitude of the corrections which the designer thought necessary in order to satisfy the eye. The long lines of the architrave--the beam which surmounts the columns or extends from column to column--would appear to sag if it were actually straight. This is also true of the stylobate, or substructure of a colonnade, and of pediments and other features. These lines were often convex instead of being straight as the eye desires to see them.

In the Parthenon, the stylobate has an upward curvature of more than four inches on the sides of the edifice and of more than two and a half inches on the east and west fronts. Vertical features were made to incline inward in order to correct the common appearance of leaning outward at the top. In the Parthenon, the axes of the columns are not vertical, but they are inclined inward nearly three inches. They are said also to be inclined toward each other to such a degree that they would meet at an altitude of one mile above the ground. The eleven-foot frieze and architrave is inclined inward about one and one-half inches.

In Fig. 85, a represents the front of a temple as it should appear; b represents its appearance (exaggerated) if it were actually built like a without compensations for optical illusions; c represents it as built and showing the physical corrections (exaggerated) in order that it may appear to the eye as a does.

Tall columns if they are actually straight are likely to appear somewhat shrunken in the middle; therefore they are sometimes made slightly swollen in order to appear straight. This outward curvature of the profile is termed an entasis and in the Parthenon column, which is thirty-four feet in height, amounted to about three-fourths of an inch. In some early Grecian works, it is said that this correction was overdone but that its omission entirely is quite unsatisfactory. Some authorities appear to believe that an excellent compromise is found in the Parthenon columns.

One of the conditions which is responsible for certain illusions and has been compensated for on occasions is represented in Fig. 86. On the left are a series of squares of equal size placed in a vertical row. If these are large so that they might represent stories in a building they will appear to decrease in size from the bottom upward, because of the decreasing projection at the eye. This is obvious if the eye is considered to be at the point where the inclined lines meet. In order to compensate for the variation in visual angle, there must be a series of rectangles increasing considerably in height toward the top. The correction is shown in the illustration. It is stated that an inscription on an ancient temple was written in letters arranged vertically, and in order to make them appear of equal size they were actually increased in size toward the top according to the law represented in Fig. 86. Obviously a given correction would be correct only for one distance in a given plane.

In Chapter VIII the phenomenon of irradiation was discussed and various examples were presented. It exerts its influence in the arts as elsewhere. Columns viewed against a background of white sky appear of smaller diameter than when they are viewed against a dark background. This is illustrated in Fig. 87 where the white and the black columns are supposed to be equal in diameter.

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. 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 illusion. It may be of interest for the reader to refer to preceding chapters and to ascertain what types of 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 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. Such 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 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. 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 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 powerful enough to resist the obliterating effect of overcast skies but notwithstanding all precautions the expression of an exterior varies considerably with nature's lighting. 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, 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.

XIV

MIRROR MAGIC

Strictly speaking there are fewer illusions found in the practice of the magician than is generally supposed; that is, the eye usually delivers correctly to the intellect, but the judgment errs for various reasons. The "illusion" is due to false assumptions, to the distracting words, to unduly accented superfluous movements of the magician; or in general to downright trickery. Much of the magician's success is due to glibness of tongue and deftness of fingers, but many of the more notable "tricks" were those involving the use of mirrors and the control of light. Black curtains, blackened assistants, and controlled light have played prominent parts in the older magic, but the principles of these are easily understood. However, the mirror perhaps has done more to astound the audience than any other device employed by the magician. For this reason, and because its effects are commonly termed illusions, some representative examples will be presented.

In a previous chapter attention was called to the simple but usually overlooked fact that, for example, the image of a face in a mirror is reversed as to right and left. When this fact is overlooked we may be astonished at the changed expression of an intimate friend as we view the face (reversed) in the mirror. Similarly our own features are reversed as to right and left and we are acquainted with this reversed image rather than the appearance of our face as it is. Inasmuch as faces are not accurately symmetrical and many are quite unsymmetrical the effects of the mirror are sometimes startling. It might be of interest for the reader to study his face in the mirror and note that the right ear is the left ear of the image which he sees. He will also find it of interest to compare the face of a friend as viewed directly with the appearance of its image in the mirror. If he desires to see himself as others see him, he can arrange two mirrors vertically almost at a right-angle. By a little research he will find an image of his own face, which is not reversed; that is, an image whose right ear is really his right ear.

A famous "illusion" which astounded audiences was the sphinx illustrated in Fig. 90. The box was placed upon a table and when opened there was revealed a Sphinxian head, but why it was called a Sphinx is clothed in mystery because upon some occasions it talked. As a matter of fact it belonged to a body which extended downward from the table-top and this kneeling human being was concealed from the audience by two very clean plate-glass mirrors M shown in the accompanying diagram. The table actually appeared to have three legs but the audience if it noticed this at all assumed the fourth leg was obscured by the foremost leg. The walls, floor, and ceiling of the box-like recess in which the table was placed were covered with the same material. It is seen by the diagram that the mirrors M reflected images of the side walls W and these images were taken by the audience to be portions of the rear wall W. Thus the table appeared to be open underneath and the possibilities of the apparatus are evident.