Optical illusion

“ An optical illusion.
courage to get up and go and place yourself in the position which appears to be occupied by the spectre, in order to demonstrate to yourself positively that it is only a vision? ”

“ Another interesting example of optical illusion is the luminous sensation produced internally when the eye, or the neighbouring parts, are struck or stimulated by friction or electricity. These appearances are experienced even by those who have lost their sight. ”

“ This kind of explanation is quite in line with the peculiarity of the onlooker-consciousness, noted earlier, to attribute an optical illusion to the eye's way of working, while charging the mind with the task of clearing up the illusion. In reality it is just the reverse. Since the intellect can form no other idea of the act of seeing than that this is a passive process taking place solely within the eye, it falls, itself, into illusion. ”

“ For, on the one hand, if touch and sight function alike in our judgment of space, we should expect that like peripheral disturbances in the two senses would cause like central errors in judgment, and every tactual analogue of an optical illusion should be found to correspond both in the direction of the error and, to a certain extent, quantitatively with the optical illusion. ”

“ There is an optical illusion about every person we meet. ”

“ Then, too, the optical studies are more attractive by reason of the comparative ease and certainty with which the statistics are gathered there. An optical illusion is discovered in a single instance of the phenomenon. ”

“ It does not occur to him that the peculiarities of optical illusion are part and parcel of our daily experience, and that we build up our world by inference over and beyond them. The artist has no interest in the dead level of scientific law ”

“ My reason told me that what I had just seen near Beddgelert was an optical illusion. I had become very learned on the subject of optical illusions ever since I had known Sinfi Lovell, and especially since I had seen that picture of Winnie in the water near Bettws y Coed, which I have described in an earlier chapter. Every book I could get upon optical illusions I had read, and I was astonished to find how many instances are on record of illusions of a much more powerful kind than mine. ”

“ And thus it may happen that, perfectly open and fair as the inquiry seems, the circumstances will insure a one-sided representation.
A familiar optical illusion well illustrates the nature of these illusions which often deceive sociological inquirers: When standing by a lake-side in the moonlight, you see, stretching over the rippled surface toward the moon, a bar of light which, as shown by its nearer part, consists of flashes from the sides of separate wavelets. You walk, and the bar of light seems to go with you. ”

“ Optical delusion adds still more to the effect. Every proportion changes. The eye is deceived and deceives itself, at the same time, with these sublime lights and deepening shades, all calculated to increase the illusion. ”

“ 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.
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 ”

“ This general law being interfered with by the expansion of the lower layers, refraction of the light rays,—or the deviation which they suffer in passing from one medium into another of differing density—takes place in a manner contrary to that when the atmospheric layers are normally superposed, and the mirage [1] is produced, an optical illusion, which causes us to see objects, below the horizon or in the air, inverted. ”

“ Of all the senses none is more frequently the seat of such deceptive judgments than that of sight; and in the science of physiological optics a very considerable share of attention is claimed by optical illusions. For the purposes of convenience, we may draw a distinction between these illusions, which are the direct result of certain properties or imperfections of the eye as an optical instrument, and those which arise from obliquities of judgment in interpreting the sensations optically impressed upon the retina of the eye. ”

“ Without affirming that optical illusions are the cause of all the supposed supernatural appearances of which we have heard so much, there is no doubt that in many instances the eye plays an important part in deluding the brain. ”

“ One of the numerous optical illusions which have from time to time been evolved by scientific minds, is that of making an image or picture appear in the air. This is produced by means of a mirror, and an object in relief, upon which a strong light is thrown,—the mirror being set at such an angle as to throw up the reflection of the image to a certain point in the view of the spectator. ”

“ Obviously, the eye is the connecting link between objective reality and visual perception and, therefore, it plays an important part in illusions. In fact, sometimes it is solely responsible for the illusion. The process of vision may be divided into several steps such as (1) the lighting, color, character, and disposition of objects; (2) the mechanism by which the image is formed upon the retina; (3) various optical defects of this mechanism; (4) the sensitiveness of the parts of the retina to light and color; (5) the structure of the retina ”

“ A picture which has struck us during the day will reappear to us at night during sleep, with every detail perfect, or possibly under a form modified by the capricious wanderings of our thoughts. A sudden fright may sometimes be the cause of optical illusions which will pursue us unceasingly. ”

“ Optical illusions generally result from the mind’s faulty interpretation of phenomena presented to it through the medium of the visual organs. They are of many different kinds, but a large class, which at first sight may seem to have little or nothing in common, arise, I believe, from a single cause, namely, the inability of the mind to form and adhere to a definite scale or standard of measurement. ”

“ OPTICAL ILLUSIONS. Besides the errors of sight already spoken of, there are other illusions, which are either common to all persons or confined to certain individuals, the knowledge of which will serve as a fitting prelude to the descriptions of those which are artificial. ”

“ 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. ”

“ Their chief tool was philosophy, the experimental attack being left to the scientists of the modern age. However, they established philosophically such principles as “space and time are not realities of the phenomenal world but the modes under which we see things apart.” As science became organized during the present experimental era, measurements were applied and there began to appear analytical discussions of various subjects including optical illusions. ”

“ Hence, although optical illusions are of many diverse kinds—illusions of color, illusions of form, illusions of size, illusions of distance, illusions of solidity, and illusions of motion—they have all to be considered from the twofold standpoint, the purely optical and the psychological. ”

“ And if this force could act upon our perceptions without a material point in which to reside, is it not reasonable to suppose that it would occasionally so do, and that we should sometimes perceive effects for which we could find no cause in the material world—no connection with matter? Yet in the whole range of human experience no such thing is known. Even the phenomena which we call optical illusions arise from certain derangements of the atomic particles of the medium through which the impression is conveyed. ”

“ Doubtless thoughtful observers ages ago noticed visual illusions, especially those found in nature and in architecture. When it is considered that geometrical figures are very commonly of an illusory character it appears improbable that optical illusions could have escaped the keenness of Euclid. The apparent enlargement of the moon near the horizon and the apparent flattened vault of the sky were noticed at least a thousand years ago and literature yields several hundred memoirs on these subjects. ”

“ he believed in the straight line,—a respectable optical illusion which has ruined many men. ”

“ As a rule optical illusions occur when there is an interruption in the communication between the retina, the sense of movement, and the sense of touch, or when we are prevented from reducing the changes of the retinal image to the movement of our body or of our eyes. ”

“ There are, however, a number of optical illusions which illustrate certain defects of our vision that cannot be corrected, no matter how much we may desire to see correctly. We continue to see them not as they are but as they seem, and we must correct our vision by information from other sources. ”

“ These glimpses of the depths to which one must dig if he is to unearth the complete explanations of visual perception—and consequently of illusions—indicate the futility of treating the theories in the available space without encroaching unduly upon the aims of this volume.
Certain defects of the optical system of the eye must contribute toward causing illusions. Any perfect lens of homogeneous material has at least two defects, known as spherical and chromatic aberration. ”

“ It is a crude mind that would insist that these appearances are not real, that the eye does not see them when all eyes behold them. To say dogmatically that any new thing seen by half-light is an illusion, is like arguing that a discovery by the telescope or microscope is unreal. ”

“ Such a pattern can be made photographically by rotating before a photographic plate a disk with openings arranged properly in steps.
Many demonstrations of the chief illusion of brightness-contrast are visible at night under glaring lighting conditions. It is difficult or impossible to see objects beyond automobile headlights, and adjacent to them, in the visual field. Objects similarly located in respect to any surface sufficiently bright are more or less obscured. ”

“ The foci of optics are proofs of the illusion of what is termed material sense, as when sky and tree-tops appear to join hands, and clouds and ocean to meet and mingle, when they are as remote at the farther as at the nearer point of vision. ”

“ A fact in practical optics, calculated to affect some observations rather seriously, has been discovered within the last few years. It is this: When a white body is viewed on a dark ground, its size is exaggerated by some illusion of our vision; and, on the contrary, a dark body seen on a bright ground appears smaller than it would were the ground of a dark color, differing from that of the body only as much as is required to render them distinguishable. ”

“ Many illusions of brightness-contrast are visible on every hand. For example, the point at which the mullions of a window cross will be seen to appear brighter than the remaining portions of them when viewed against a bright sky. Conversely, in Fig. 64, dark spots appear where the white bars cross. This is purely an illusion and the same type may be witnessed by the observant many times a day. In Fig. 64 it is of interest to note that the illusion is weak for the crossing upon which the point of sight rests, but by averted vision the illusion is prominent for the [Pg 119] other crossings. ”

“ In addition to the colors of the spectrum there are a vast number of vibratory color waves, some too low and others too high to be registered by the human optical apparatus. It is appalling to contemplate man's colossal ignorance concerning these vistas of abstract space. As in the past man explored unknown continents, so in the future, armed with curious implements fashioned for the purpose, he will explore these little known fastnesses of light, color, sound, and consciousness. ”

“ All the illusions of imperfect sight are the result of a strain of the mind, and when the mind is disturbed for any reason illusions of all kinds are very likely to occur. This strain is not only different from the strain that produces the error of refraction, but it can be demonstrated that for each and every one of these illusions there is a different kind of strain. Alterations of color do not necessarily affect the size or form of objects, or produce any other illusion, and it is possible to see the color of a letter, or of a part of a letter, perfectly, without recognizing the letter. ”

“ If the variation in the position of the eyes is held to account for the illusion, this explanation may be supported by using a horizontal telescope with adjustable cross-hairs, and a mirror. By varying the position of the latter the disk of the sun may be measured at any altitude without varying the position of the eye. When everything is eliminated from the field but the moon’s disk, it is found to be constant in size. However, this is not conclusive evidence that the variation in the position of the line of sight accounts for the illusion. ”

“ The peculiar appearances known as spectres in optics are certain illusions of vision in which an object is apparently presented to the view which does not really exist. In such cases either the brain, the retina, or the optic nerve are unnaturally excited, and made sensitive to an appearance that, physically speaking, does not exist. There is such a close connexion between the senses and the mind, that we continually, and without knowing it, transfer to the physical world that which belongs to the domain of thought. ”