Visual Illusions Part 11

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.

[Ill.u.s.tration: Fig. 87.--Irradiation in architecture.]

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 princ.i.p.al 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.

[Ill.u.s.tration: Fig. 88.--Some simple geometrical-optical illusions in architecture.]

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 ma.s.s 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.

[Ill.u.s.tration: Fig. 89.--By decreasing the exposed length of shingles toward the top a greater apparent expanse is obtained.]

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 pa.s.sing 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 a.s.sumptions, 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 a.s.sistants, 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 ill.u.s.trated 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-gla.s.s mirrors _M_ shown in the accompanying diagram. The table actually appeared to have three legs but the audience if it noticed this at all a.s.sumed 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.

[Ill.u.s.tration: Fig. 90.--An example of a "mirror" illusion.]

The magician with a fine flow of language could dwell at length upon the coming to life of the head of an ancient statue which he had in the box in his hand. Walking to the table he could place the box over a trap-door and by the time he had unlatched the door of the box, the a.s.sistant kneeling under the table could have his head thrust upward through the trap-door of the table-top into the box. After a few impressive words, supposed to be Hindoo but in reality were Hoodoo, presto! and the Sphinx was revealed.

It conversed after a period of silence extending back to the days of Rameses when a wrathful G.o.d condemned an unfortunate king to imprisonment in the stone statue. The original trick awed audiences for many nights and defied explanation until one night a keen observer noted finger-prints on what proved to be a mirror. Doubtless a careless accomplice lost his job, but the damage had been done, for the trick was revealed. This "illusion"

is so effective that it, or variations of it, are still in use.

[Ill.u.s.tration: Fig. 91.--Another example of "mirror magic."]

Another simple case is ill.u.s.trated in Fig. 91. A large plate-gla.s.s mirror _M_ was placed at an angle of approximately 45 degrees from the floor.

Through a hole in it an a.s.sistant's head and shoulders projected and the edge of the opening was covered with a draped cloth. The audience saw the image of the ceiling _C_ of the alcove reflected by the mirror but being ignorant of the presence of the mirror, a.s.sumed this image to be the rear wall. This trick was effective for many years. Obviously the mirrors must be spotlessly clean and the illuminations of the walls, ceiling, and in some cases, the floor must be very uniform. Furthermore, no large conspicuous pattern could be used for lining the box-like recess.

The foregoing examples ill.u.s.trate the principles involved in the appearance of ghosts on the stage and of a skeleton or other gruesome object in place of a human being. The possibilities of mirrors in such fields are endless and they can be studied on a small scale by anyone interested. The pseudoscope which produces effects opposite to those of the stereoscope is an interesting device.

The foregoing is the faintest glimpse of the use of the mirror, but it does not appear advisable to dwell further upon its use, for after all the results are not visual illusions in the sense of the term as usually employed throughout this book.

XV

CAMOUFLAGE

Illusions played many roles in the science and art of deception during the World War, but they served most prominently in the later stages of the war upon the sea. Inasmuch as the story of the science of camouflage is not generally available, it appears worth while to present it briefly. Besides being of interest, it will reveal to the reader the part that the science of light, color, lighting, and vision played in deception. Furthermore, the reader will sense the numberless illusions which are woven into camouflage as developed in nature, and in human activities. The word _camouflage_ by origin does not include all kinds of deception; however, by extension it may and will here signify almost the entire art and science of deception as found in nature and as practiced in the World War.

_Terrestrial Camouflage._--Camouflage is an art which is the natural outgrowth of our instinct for concealment and deception when pitting our wits against those of a crafty prey or enemy. It is an art older than the human race, for its beginnings may be traced back to the obscurity of the early ages of the evolution of animal life. The name was coined by the French to apply to a definite art which developed during the Great War to a high state, as many other arts developed by drawing deeply upon the resources of scientific knowledge. With the introduction of this specific word to cover a vast field of activity in scientifically concealing and deceiving, many are led to believe that this is a new art, but such is not the case. However, like many other arts, such as that of flying, the exigencies of modern warfare have provided an impetus which has resulted in a highly developed art.

Scientists have recognized for many years, and perhaps more or less vaguely for centuries, that Nature exhibits wonderful examples of concealment and deception. The survival of the fittest, as Darwin expressed his doctrine, included those individuals of a species who were best fitted by their markings and perhaps by peculiar habits to survive in the environment in which they lived. Naturally, markings, habits, and environment became more and more adapted to each other until the species became in equilibrium with Nature sufficiently to insure its perpetuity.

If we look about us upon animal life we see on every hand examples of concealing coloration and att.i.tudes designed to deceive the prey or enemy.

The rabbit is mottled because Nature's infinite variety of highlights, shadows, and hues demand variety in the markings of an animal if the latter is to be securely hidden. Solid color does not exist in Nature's landscapes in large areas. The rabbit is lighter underneath to compensate for the lower intensity of illumination received on these portions. As winter approaches, animals in rigorous climates need warmer coats, and the hairs grow longer. In many cases the color of the hairs changes to gray or white, providing a better coating for the winter environment.

Animals are known to mimic inanimate objects for the sake of safety. For example, the bittern will stand rigid with its bill pointed skyward for many minutes if it suspects an enemy. Non-poisonous snakes resemble poisonous ones in general characteristics and get along in the world on the reputation of their harmful relatives. The drone-bee has no sting, but to the casual observer it is a bee and bees generally sting. Some animals have very contrasting patterns which are conspicuous in shape, yet these very features disguise the fact that they are animals. Close observation of fishes in their natural environment provides striking examples of concealing coloration. Vast works have been written on this subject by scientists, so it will only be touched upon here.

There are many examples of "mobile" camouflage to be found in Nature.

Seasonal changes have been cited in a foregoing paragraph. The chameleon changes its color from moment to moment. The flounder changes its color and _pattern_ to suit its environment. It will even strive to imitate a black and white checkerboard.

In looking at a bird, animal, insect, or other living thing it is necessary to place it in its natural environment at least in the imagination, before a.n.a.lyzing its coloration. For example, a male mallard duck hanging in the market is a very gaudy object, but place it in the pond among the weeds, the green leaves, the highlights, and the shadows, and it is surprisingly inconspicuous. The zebra in the zoo appears to be marked for the purpose of heralding its presence anywhere in the range of vision, but in its reedy, bushy, gra.s.sy environment it is sufficiently inconspicuous for the species to survive in Nature's continuous warfare.

Thus studies of Nature reveal the importance of general hue, the necessity for broken color or pattern, the fact that black spots simulate shadows or voids, the compensation for lower illumination by counter-shading, and many other facts. The artist has aided in the development of camouflage, but the definite and working basis of all branches of camouflage are the laws and facts of light, color, and vision as the scientist knows them.

Just as lower animal life has unconsciously survived or evolved by being fitted to do so, mankind has consciously, or at least instinctively, applied camouflage of various kinds to fool his prey or his enemy. Many of us in hunting ducks have concealed the bow of our sneak-boat with mud and weeds, or in the season of floating ice, with a white cloth. In our quest of water fowl we use decoys and gra.s.s suits. The Esquimau stalks his game behind a piece of ice. In fact, on every hand we find evidences of this natural instinct. The Indian painted his face and body in a variety of colors and patterns. Did he do this merely to be hideous? It seems very possible that the same instinct which made him the supreme master of wood-craft caused him to reap some of the advantages of concealment due to the painting of his face and body.

In past wars there is plenty of evidence that concealment and deception were practiced to the full extent justifiable by the advantages or necessity. In the World War the advent of the airplane placed the third dimension in reconnaissance and called for the application of science in the greatly extended necessity for concealment and deception. With the advent of the airplane, aerial photography became a more important factor than visual observation in much of the reconnaissance. This necessitated that camouflage in order to be successful had to meet the requirements of the photographic eye, as well as that of the human eye. In other words, the special characteristics of the colors used had to be similar to those of Nature's colors. For example, chlorophyl, the green coloring matter of vegetation, is a peculiar green as compared with green pigments. When examined with a spectroscope it is seen to reflect a band of deep red light not reflected by ordinary pigments. In considering this aspect it is well to bear in mind that the eye is a synthetic apparatus; that is does not a.n.a.lyze color in a spectral sense. An artist who views color subjectively and is rarely familiar with the spectral basis may match a green leaf perfectly with a mixture of pigments. A photographic plate, a visual filter, or a spectroscope will reveal a difference which the unaided eye does not.

Some time before the Great War began, it occurred to the writer that colored filters could be utilized in aiding vision by increasing the contrast of the object to be viewed against its surroundings.[9] Studies were made of various filters, made with the object of the experiment in mind, in viewing the uniforms of various armies. Further developments were made by applying the same principles to colored lights and painted pictures. Many of these have been described elsewhere. With the development of the science of camouflage, filters came into use for the detection of camouflage. As a result of the demand for avoiding detection by photographic plates and by various colored filters, some paints provided for the camoufleur were developed according to the spectral requirements. Many other applications of science were developed so that camouflage can now be called an art based upon sound scientific principles.

Natural lighting is so variable that it is often impossible to provide camouflage which will remain satisfactory from day to day; therefore, a broad knowledge of Nature's lighting is necessary in order to provide the best compromise. There are two sources of light in the daytime, namely, the sun and the sky. The relative amounts of light contributed by these two sources is continually changing. The sky on cloudless days contributes from one-tenth to one-third of the total light received by a horizontal surface at noon. Light from the sky and light reflected from the surroundings illuminate the shadows. These shadows are different in color than highlights, although these finer distinctions may be ignored in most camouflage because color becomes less conspicuous as the distance of observation increases. In general, the distribution of brightness or light and shade is the most important aspect to be considered.

The camoufleur worries over shadows more than any other aspect generally.

On overcast days camouflage is generally much more successful than on sunny days. Obviously, counter-shading is resorted to in order to eliminate shadows, and where this is unsuccessful confusion is resorted to by making more shadows. The shape and orientation of a building is very important to those charged with the problem of rendering it inconspicuous to the enemy, but little attention has been paid to these aspects. For example, a hangar painted a very satisfactory dull green will be distinguishable by its shape as indicated by its shadow and shaded sides.

In this zone a hangar, for example, would be more readily concealed if its length lay north and south. Its sides could be brought with a gradual curve to the ground and its rear, which is during most of the day in shadow, could be effectively treated to conceal the shadow. A little thought will convince the reader of the importance of shape and orientation.

Broken color or pattern is another fundamental of camouflage which, of course, must be adapted to its environment. For our trucks, cannon, and many other implements of war, dark green, yellow, dark blue, light gray, and other colors have been used in a jumble of large patterns. A final refinement is that of the blending of these colors at a distance, where the eye no longer resolves the individual patches, to a color which simulates the general hue of the surroundings. For example, red and green patches at a distance blend to yellow; yellow and blue patches blend to a neutral gray if suitably balanced, but if not, to a yellow-gray or a blue-gray; red, green, and blue if properly balanced will blend to a gray; black, white and green patches will blend to a green shade, and so on.

These facts are simple to those who are familiar with the science of light and color, but the artist, whose knowledge is based upon the mixture of pigments, sometimes errs in considering this aspect of color-blending by distance. For example, it is not uncommon for him to state that at a distance yellow and blue patches blend to make green, but the addition of lights or of juxtaposed colors is quite different in result from the addition of pigments by intimately mixing them.

In constructing such a pattern of various colors it is also desirable to have the final mean brightness approximate that of the general surroundings. This problem can be solved by means of the photometer and a formula provided, which states, for example, that a certain percentage of the total area be painted in gray, another percentage in green, and so on.

The photometer has played an important role in establishing the scientific basis of camouflage. The size of the pattern must be governed by the distance at which it is to be viewed, for obviously if too small the effect is that of solid color, and if too large it will render the object conspicuous, which is a disadvantage ranking next to recognizable.