University of Virginia Library

Section 99. (2) Optical Illusions.

It will be best to begin the study of optical illusions with the consideration of those conditions which cause extraordinary, lunatic images. They are important because the illusion is recognizable with respect to the possibility of varied interpretations by any observer, and because anybody may experiment for himself with a bit of paper on the nature of false optical apprehension. If we should demonstrate no more than that the simplest conditions often involve coarse mistakes, much will have been accomplished for the law, since the "irrefutable evidence" of our senses would then show itself to need corroboration. Nothing is proved with "I have seen it myself," for a mistake in one point shows the equal possibility of mistakes in all other points.

Generally, it may be said that the position of lines is not without influence on the estimation of their size.[1] Perpendicular dimensions are taken to be somewhat greater than they are. Of two crossed lines, the vertical one seems longer, although it is really equal to the horizontal one. An oblong, lying on its somewhat longer side, is taken to be a square; if we set it on the shorter side it seems to be still more oblong than it really is. If we divide a square into equal angles we take the nearer horizontal ones to be larger, so that we often take an angle of thirty degrees to be forty-five. Habit has much influence here. It will hardly be believed, and certainly is not consciously known, that in the letter S the upper curve has a definitely smaller radius than the lower one; but the inverted S shows this at once. To such types other false estimations belong: inclinations, roofs, etc., appear so steep in the distance that it is said to be impossible to move on them without especial help. But whoever does move on them finds the inclination not at all so great. Hence, it is necessary, whenever the ascension of some inclined plane is declared impossible, to inquire whether the author of the declaration was himself there, or whether he had judged the thing at a distance.

Slight crooks are underestimated. Exner[2] rightly calls attention to the fact that in going round the rotunda of the Viennese Prater, he always reached the exit much sooner than he expected. This is due to the presence of slight deviations and on them are based the numerous false estimates of distance and the curious fact that people, on being lost at night in the woods, go round in a significantly small circle. It is frequently observed that persons, who for one reason or another, i. e., robbery, maltreatment, a burglarious assault, etc., had fled into the woods to escape, found themselves at daybreak, in spite of their flight, very near the place of the crime, so that their honesty in fleeing seems hardly believable. Nevertheless it may be perfectly trustworthy, even though in the daytime the fugitive might be altogether at home in the woods. He has simply underestimated the deviations he has made, and hence believes that he has moved at most in a very flat arc. Supposing himself to be going forward and leaving the wood, he has really been making a sharp arc, and always in the same direction, so that his path has really been circular.

Some corroboration for this illusion is supplied by the fact that the left eye sees objects on the left too small, while the right eye underestimates the right side of objects. This underestimation varies from 0.3 to 0.7%. These are magnitudes which may naturally be of importance, and which in the dark most affect deviations that are closely regarded on the inner side of the eye—i. e., deviations to the left of the left eye or the right of the right eye.

Such confusions become most troublesome when other estimations are added to them. So long as the informant knows that he has only been estimating, the danger is not too great. But as a rule the informant does not regard his conception as an estimate, but as certain knowledge. He does not say, "I estimate," he says, "It is so." Aubert tells how the astronomer Förster had a number of educated men, physicians, etc., estimate the diameter of the moon. The estimation varied from 1" to 8" and more. The proper diameter is 1.5" at a distance of 12".

It is well known that an unfurnished room seems much smaller than a furnished one, and a lawn covered with snow, smaller than a thickly-grown one. We are regularly surprised when we find an enormous new structure on an apparently small lot, or when a lot is parcelled out into smaller building lots. When they are planked off we marvel at the number of planks which can be laid on the surface.

The illusions are still greater when we look upward. We are less accustomed to estimation of verticals than of horizontals. An object on the gutter of a roof seems much smaller than at a similar distance on the ground. This can be easily observed if any figure which has been on the roof of a house for years is once brought down. Even if it is horizontally twice as far as the height of the house, the figure still seems larger than before. That this illusion is due to defective practice is shown by the fact that children make mistakes which adults find inconceivable. Helmholtz tells how, as child, he asked his mother to get him the little dolls from the gallery of a very high tower. I remember myself that at five years I proposed to my comrades to hold my ankles so that I could reach for a ball from the second story of a house down to the court-yard. I had estimated the height as one-twelfth of its actual magnitude. Certain standards of under and overestimations are given us when there is near the object to be judged an object the size of which we know. The reason for the fact that trees and buildings get such ideal sizes on so-called heroic landscape is the artistically reduced scale. I know that few pictures have made such a devilish impression on me as an enormous landscape, something in the style of Claude Lorraine, covering half a wall. In its foreground there is to be seen a clerk riding a horse in a glen. Rider and horse are a few inches high, and because of this the already enormous landscape becomes frightfully big. I saw the picture as a student, and even now I can describe all its details. Without the diminutive clerk it would have had no particular effect.

In this connection we must not forget that the relations of magnitude of things about us are, because of perspective, so uncertain that we no longer pay any attention to them. "I find it difficult," says Lipps,[3] "to believe that the oven which stands in the corner of the room does not look larger than my hand when I hold it a foot away from my eyes, or that the moon is not larger than the head of a pin, which I look at a little more closely.... We must not forget how we are in the custom of comparing. I compare hand and oven, and I think of the hand in terms of the oven." That is because we know how large the hand and the oven are, but very often we compare things the sizes of which we do not know, or which we can not so easily get at, and then there are many extraordinary illusions.

In connection with the cited incident of the estimation of the

moon's diameter, there is the illusion of Thomas Reid who saw that the moon seemed as large as a plate when looked at with the unhampered eye, but as large as a dollar when looked at through a tube. This mistake establishes the important fact that the size of the orifice influences considerably the estimation of the size of objects seen through it. Observations through key-holes are not rarely of importance in criminal cases. The underestimations of sizes are astonishing.

Aërial perspective has a great influence on the determination of these phenomena, particularly such as occur in the open and at great distances. The influence is to be recognized through the various appearances of distant objects, the various colors of distant mountains, the size of the moon on the horizon, and the difficulties which aërial perspective offers painters. Many a picture owes

its success or failure to the use of aërial perspective. If its influence is significant in the small space of a painting, the illusions in nature can easily become of enormous significance, particularly when extremes are brought together in the observations of objects in unknown regions. The condition of the air, sometimes foggy and not pellucid, at another time particularly clear, makes an enormous difference, and statements whether about distance, size, colors, etc., are completely unreliable. A witness who has several times observed an unknown region in murky weather and has made his important observation under very clear skies, is not to be trusted.

An explanation of many sensory illusions may be found in the so-called illusory lines. They have been much studied, but Zöllner[4] has been the first to show their character. Thus, really quite parallel lines are made to appear unparallel by the juxtaposition of inclined or crossing lines. In figures 1 and 2 both the horizontal lines are actually parallel, as may be determined in various ways.

The same lines looked at directly or backwards seem, in Fig. 1, convex, in Fig. 2 concave.

Still more significant is the illusion in Fig. 3, in which the convexity is very clear. The length, etc., of the lines makes no difference in the illusion.

On the other hand, in Fig. 4 the diagonals must be definitely thicker than the parallel horizontal lines, if those are to appear not parallel. That the inclination is what destroys the appearance of parallels is shown by the simple case given in Fig. 5, where the distance from A to B is as great as from B to C, and yet where the first seems definitely smaller than the second.

Still more deceptive is Fig. 6 where the first line with the angle inclined inwards seems incomparably smaller than the second with the angle inclined outwards.

All who have described this remarkable subject have attempted to explain it. The possession of such an explanation might put

us in a position to account for a large number of practical difficulties. But certain as the facts are, we are still far from their why and how. We may believe that the phenomenon shown in Figs. 1 and 2 appears when the boundaries of a field come straight up to a street with parallel sides, with the result that at the point of meeting the street seems to be bent in. Probably we have observed this frequently without being aware of it, and have laid no particular stress on it, first of all, because it was really unimportant, and secondly, because we thought that the street was really not straight at that point.

In a like manner we may have seen the effect of angles as shown in Figs. 5 and 6 on streets where houses or house-fronts were built cornerwise. Then the line between the corners seemed longer or shorter, and as we had no reason for seeking an accurate judgment

we paid no attention to its status. We simply should have made a false estimate of length if we had been required to judge it. It is also likely that we may have supposed an actual or suppository line on the side of the gables of a house enclosed by angles of the gables, to be short,—but until now the knowledge of this supposition has had no practical value. Nevertheless, the significance of these illusions should not be underestimated. They mean most of all the fact that we really can be much deceived, even to the degree of swearing to the size of a simple thing and yet being quite innocently mistaken. This possibility shows, moreover, that the certainty of our judgment according to sensible standards is inadequate and we have no way of determining how great this inadequacy is. We have already indicated that we know only the examples cited by Zöllner, Delboeuf and others. It is probable that they were hit upon by accident and that similar ones can not be discovered empirically or intentionally. Hence, it may be assumed that such illusions occur in great number and even in large dimensions. For example, it is known that Thompson discovered his familiar "optical circle illusion" (six circles arranged in a circle, another in the middle. Each possesses bent radii which turn individually if the whole drawing is itself turned in a circle) by the accident of having seen the geometrical ornament drawn by a pupil. Whoever deals with such optical illusions may see very remarkable ones in almost every sample of ladies' clothes, particularly percale, and also in types of carpets and furniture. And these are too complicated to be described. In the course of time another collection of such illusions will be discovered and an explanation of them will be forthcoming, and then it may be possible to determine how our knowledge of their existence can be turned to practical use.

Practical application is easier in the so-called inversion of the visual object. Fig. 7 shows the simplest case of it—the possibility of seeing the middle vertical line as either deeper or higher than the others. In the first instance you have before you a gutter,

in the second a room. Similar relations are to be observed in the case of a cube in which the corner a may be seen as either convex or concave according as

you think it behind or before the background of the angles from which a proceeds. It is still clearer when, in a rhomboid, the line XY is drawn. Then x or y may be seen alternately as nearer or further and the figure can thereby be brought into a different position. (Fig. 9.) Done once it may be repeated voluntarily.

There are many practical examples of these illusions. Sinsteden saw one evening the silhouette of a windmill against a luminous background. The arms seemed now

to go to the right, now to the left—clearly because he did not make out the body of the mill and might equally assume that he saw it from the front or from the rear, the wheels going toward the right in the first, and toward the left in the other case. An analogous case is cited by Bernstein. If (Fig. 10) the cross made of the thin lines stand for the bars of a weather vane and the heavy lines represent the weather vane itself, it may be impossible under the conditions of illumination for an eye looking from N to distinguish whether the weather vane points NE or SW; there is no way of determining the starting point of motion. All that can certainly be said is that the weather vane lies between NE and SW and that

its angle is at the crossing of the two lines, but the direction in which its heads point can not be determined at even a slight distance. Both forms of this illusion may occur in a criminal trial. If once a definite idea of some form of order has been gained, it is not abandoned or doubted, and is even sworn to. If asked, for example, whether the mill-wheel moved right or left, the observer will consider hardly one time in a hundred whether there might not have been an optical illusion. He will simply assure

us that the thing was as he thinks he saw it, and whether he saw it correctly is purely a matter of luck.

To all these illusions may be added those which are connected with movement or are exposed by movement. During the movement of certain bodies we can distinguish their form only under definite conditions. As their movement increases they seem shorter in the direction of movement and as it decreases they seem broader than normally. An express train with many cars seems shorter when moving directly near us, and rows of marching men seem longer. The illusion is most powerful when we look through a stationary small opening. The same thing occurs when we move quickly past bodies, for this makes them seem very short as we go by.

Of such cases sense-illusion does not constitute an adequate explanation; it must be supplemented by a consideration of certain inferences which are, in most instances, comparatively complex.[5] We know, e. g., that objects which appear to us unexpectedly at night, particularly on dark, cloudy nights, seem inordinately magnified. The process is here an exceedingly complex one. Suppose I see, some cloudy night, unexpectedly close to me a horse whose environment, because of the fog, appears indistinct. Now I know from experience that objects which appear from indistinct environments are as a rule considerably distant. I know, further, that considerably distant objects seem much smaller, and hence I must assume that the horse, which in spite of its imaginary distance appears to retain its natural size, is really larger than it is. The train of thought is as follows: "I see the horse indistinctly. It seems to be far away. It is, in spite of its distance, of great size. How enormous it must be when it is close to me!" Of course these inferences are neither slow nor conscious. They occur in reflection with lightning-like swiftness and make no difference to the certainty of the instantaneous judgment. Hence it is frequently very difficult to discover the process and the mistake it contains.

If, however, the observer finds an inexplicable hiatus in an event he happens to notice, he finds it strange because unintelligible. In this way is created that notion of strangeness which often plays so great a rôle in the examination of witnesses. Hence when under otherwise uncomfortable conditions, I see a horse run without hearing the beat of his hoofs, when I see trees sway without feeling any storm; when I meet a man who, in spite of the moonlight, has no shadow, I feel them to be very strange because something is lacking

in their logical development as events. Now, from the moment a thing becomes strange to an individual his perceptions are no longer reliable, it is doubtful whether he knows what he has really experienced before his world became strange to him. Add to this that few people are unwilling to confess that they felt ill at ease, that perhaps they do not even know it,[6] and you get the complicated substitution of sensory illusions and uncanny sensation, the one causing the other, the other magnifying the one, and so on until the whole affair is turned into something quite unrecognizable. So we find ourselves in the presence of one of the inexplicable situations of the reality of which we are assured by the most trustworthy individuals.

To magnify this phenomenon, we need only think of a few slightly abnormal cases. It has already been indicated that there are many such which are not diseased, and further, that many diseased cases occur which are not known as such, at least, as being so much so as to make the judge call in the doctor. This is the more likely because there are frequently, if I may say so, localized diseases which do not exhibit any extraordinary symptoms, at least to laymen, and hence offer no reason for calling in experts. If we set aside all real diseases which are connected with optical illusions as not concerning us, there are still left instances enough. For example, any medical text-book will tell you that morphine fiends and victims of the cocaine habit have very strong tendencies to optical illusions and are often tortured by them. If the disease is sufficiently advanced, such subjects will be recognized by the physician at a single glance. But the layman can not make this immediate diagnosis. He will get the impression that he is dealing with a very nervous invalid, but not with one who is subject to optical illusions. So, we rarely hear from a witness that he knows such people, and certainly not that he is one himself. A very notable oculist, Himly, was the first to have made the observation that in the diseased excitability of the retina every color is a tone higher. Luminous black looks blue, blue looks violet, violet looks red, red looks yellow. Torpor of the retina inverts the substitution.

Dietz[7] tells of color-illusions following upon insignificant indigestion; Foderè of hysterics who see everything reversed, and Hoppe[8] says, "If the order of the rods and cones of the retina is somewhat disturbed by an inflammatory touch, the equilibrium of vision is

altered and changes in size, in form, or appearance occur." Naturally the criminalist can not perceive slight indigestion, weak hysteria, or an inflamed area in the retina when he is examining witnesses, yet false observations like those described may have a definite influence upon the decision in a case.

If such abnormal occasions are lacking the reasons for optical illusions are of another nature. 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. This reduction goes on so unconsciously that we see the idea of the object and its condition as a unit. Again, it is indubitable that the movement of the body seems quicker when we observe it with a fixed glance than when we follow it with our eyes. The difference may be so significant that it is often worth while, when much depends on determining the speed of some act in a criminal case, to ask how the thing was looked at.

Fechner has made a far-reaching examination of the old familiar fact that things on the ground appear to run when we ride by them rapidly.[9] This fact may be compared with the other, that when you look directly into swift-moving water from a low bridge, the latter seems all of a sudden to be swimming rapidly up stream, though the water does not appear to stand still. Here some unknown factor is at work and may exercise considerable influence on many other phenomena without our being able to observe the results. To this class may be added the extraordinary phenomenon that from the train objects easily seem too near and hence appear smaller than they are. It may be, however, that the converse is true and objects appear smaller, or at least shorter, and that inasmuch as we are in the habit of attributing the diminution of size in objects to their distance, we tax the latter as false. So much is certain—that whenever we ourselves move quickly we make false judgments of size, distance, and even color. The last may be due to the fact that during a quick passage, colors may so compose themselves, that green and red become white, and blue and yellow, green, etc. I believe that all these illusions are increasing in connection with the spread of bicycling, inasmuch as many observations are made from the fleeting wheel and its motion tends to increase the illusions considerably. Concerning the differences in movement Stricker[10]

says: "If I lie on my back and see a bird fly in the uniformly blue heaven, I recognize the movement although I have no object with which to compare it. This can not be explained by the variety of points on the retina which are affected, for when the bird pauses and I turn my eye, I know that it is not moving." The last argument is not correct. If the bird is sitting on a branch I know, in spite of all my occipital movement, that it is quiet, but only because I perceive and observe the bird's immobility. If, however, I lie on my back like Stricker and see above me a bird of the class that, so to speak, swim motionless in the air for minutes at a time, and if then I turn my head, I can not tell when the bird begins to move. Here then we have no exception to the general rule and can always say that we are speaking of movement optically perceived when the rays issuing from any body progressively touch various points on the retina. And since this occurs when we are in motion as well as when the object is in motion it happens that we can not locate the movement, we cannot say whether it be in us or in the object.

Of course, the possibility that fanciful images may appear during movement is familiar. If I sit quietly in the forest and at some distance see a stone or a piece of wood or a little heap of dried leaves, etc., it may be that, because of some illusion, I take it to be a rolled up hedgehog, and it may happen that I am so convinced of the nature of the object while I am looking at it that I see how the hedgehog stretches itself, sticks out its paws and makes other movements. I remember one winter when, because of some delay, a commission on which I was serving had failed to reach a village not far from the capital. We had gone to investigate a murder case and had found the body frozen stiff. The oven in the room was heated and the grave-digger placed the stiff body near the oven in order to thaw it out. We at this time were examining the place. After a while I was instructed by the examining justice to see about the condition of the corpse, and much to my disgust, I found it sitting near the oven, bent over. It had thawed out and collapsed. During the subsequent obduction I saw most clearly how the corpse made all kinds of movements, and even after the section, during the dictation of the protocol, my imagination still seemed to see the corpse moving a hand or a foot.

The imagination may also cause changes in color. Once, I saw on my desk, which stood next to a window, a great round drop of water on the left side of which the panes of the window were reflected. (Fig. 11). The whole business was about a meter

from my eye. I saw it repeatedly while working and it finally occurred to me to inquire how such a great drop of water could get there. I had sat at my desk for hours without moving. I must have observed it if it had dropped there. Refraining intentionally from going closer, I started, without avail, to consider how it could have

come. Some time after I examined the drop of water FIG. 11. and found it to be an ink-blot, long ago completely dried, and bearing on its left side a few grains of white cigar ash. I had taken these to be the image of the window, and hence, had immediately attached to it the idea of the shining, raised drop of water. I had altogether overlooked the deep black color of the drop. On the witness stand I would have sworn that I had seen a drop of water, even if I had known the evidence on the matter to be important.

In many cases it is possible to control the imagination, but only when it is known that the images can not be as they are seen. Everybody is aware how a half-covered object at a distance, or objects accidentally grouped in one way or another, are taken for God knows what. Thus once, looking from my desk to my smoking table, I saw an enormous pair of tailor's scissors half-covered by a letter. It remained identical under a number of repeated glances. Only when I thought vigorously that such a thing could not possibly be in my room did it disappear. A few scales of ashes, the lower round of the match safe, the metal trimmings of two cigar boxes half-covered by a letter and reflected by the uncertain light breaking through the branches of a tree, were all that the tailor's scissors was composed of. If there had been such a thing in the house, or if I had believed something like it to exist in the house, I should have sought no further and should have taken my oath that I had seen the thing. It is significant that from the moment I understood the phenomenon I could not restore the image of the scissors. How often may similar things be of importance in criminal trials!

The so-called captivation of our visual capacity plays a not unimportant part in distinguishing correct from illusory seeing. In order to see correctly we must look straight and fully at the object. Looking askance gives only an approximate image, and permits the imagination free play. Anybody lost in a brown study who pictures some point in the room across the way with his eyes can easily mistake a fly, which he sees confusedly askance, for a great big bird. Again, the type of a book seems definitely smaller if the eyes are fixed on the point of a lead pencil with a certain distance

before or above the book. And yet again, if you stand so that at an angle of about 90 degrees from the fixation point, you look at a white door in a dark wall, observing its extent in indirect vision, you will find it much higher than in direct vision.

These examples indicate how indirect vision may be corrected by later correct vision, but such correction occurs rarely. We see something indirectly; we find it uninteresting, and do not look at it directly. When it becomes of importance later on, perhaps enters into a criminal case, we think that we have seen the thing as it is, and often swear that "a fly is a big bird."

There are a number of accidents which tend to complete illusion. Suppose that the vision of a fly, which has been seen indirectly and taken for a big bird happens to be synchronous with the shriek of some bird of prey. I combine the two and am convinced that I have seen that bird of prey. This may increase, so much so that we may have series of sense-illusions. I cite the example of the decorative theatrical artist, who can make the most beautiful images with a few, but very characteristic blots. He does it by emphasizing what seems to us characteristic, e. g., of a rose arbor, in such a way that at the distance and under the conditions of illumination of the theatre we imagine we really see a pretty rose arbor. If the scene painter could give definite rules he would help us lawyers a great deal. But he has none, he proceeds according to experience, and is unable to correct whatever mistakes he has committed. If the rose arbor fails to make the right impression, he does not try to improve it—he makes a new one. This may lead to the conclusion that not all people require the same characteristics in order to identify a thing as such, so that if we could set the rose arbor on the stage by itself, only a part of the public would recognize it as properly drawn, the other part would probably not recognize it at all. But if, of an evening, there is a large number of decorations on the stage, the collective public will find the arbor to be very pretty. That will be because the human senses, under certain circumstances, are susceptible to sympathetic induction. In the case of the rose arbor we may assume that the artist has typically represented the necessary characteristics of the arbor for one part of the audience, for another part those of a castle, for another part those of a forest, and for a fourth those of a background. But once an individual finds a single object to be correct, his senses are already sympathetically inductive, i. e., captivated for the correctness of the whole collection, so that the correctness passes from one object to the total

number. Now, this psychic process is most clear in those optical illusions which recently have been much on public exhibition (the Battle of Gravelotte, the Journey of the Austrian Crown Prince in Egypt, etc.). The chief trick of these representations is the presenting of real objects, like stones, wheels, etc., in the foreground in such a way that they fuse unnoticeably with the painted picture. The sense of the spectator rests on the plastic objects, is convinced of their materiality and transfers the idea of this plasticity to the merely pictured. Thus the whole image appears as tri-dimensional.

The decorations of great parks at the beginning of the last century indicate that illumination and excited imagination are not alone in causing such illusions. Weber tells ecstatically of an alley in Schwetzing at the end of which there was a highly illuminated concave wall, painted with a landscape of mountains and water-falls. Everybody took the deception for a reality because the eye was captivated and properly inducted. The artist's procedure must have been psychologically correct and must have counted upon the weakness of our observation and intellection. Exner points to the simple circumstance that we do not want to see that things under certain conditions must terminate. If we draw a straight line and cover an end with a piece of paper, every one wonders that the line is not longer when the paper is removed.

I know of no case in criminal procedure where illusions of this kind might be of importance, but it is conceivable that such illusions enter in numberless instances. This is especially susceptible of observation when we first see some region or object hastily and then observe it more accurately. We are astonished how fundamentally false our first conception was. Part of this falseness may be adduced to faults of memory, but these play little or no part if the time is short and if we are able to recall that the false conception appeared just as soon as we observed the situation in question. The essential reason for false conception is to be found only in the fact that our first hasty view was incorrectly inducted, and hence, led to illusions like those of the theatre. Thus, it is possible to take a board fence covered at points with green moss, for a moss-covered rock, and then to be led by this to see a steep cliff. Certain shadows may so magnify the size of the small window of an inn that we may take it to be as large as that of a sitting room. And if we have seen just one window we think all are of the same form and are convinced that the inn is a mansion. Or again, we see, half-covered, through the woods, a distant pool, and in memory we then see the possibly,

but not necessarily, present river. Or perhaps we see a church spire, and possibly near it the roof of a house rises above the trees; then we are inducted into having seen a village, although there really are visible only the church and the house.

These illusions again, I must repeat, are of no importance if they are at all doubted, for then the truth is ascertained. When, however, they are not doubted and are sworn to, they cause the greatest confusion in trials. A bar-room quarrel, a swung cane, and a red handkerchief on the head, are enough to make people testify to having seen a great brawl with bloody heads. A gnawing rat, a window accidentally left open through the night, and some misplaced, not instantaneously discovered object, are the ingredients of a burglary. A man who sees a rather quick train, hears a shrill blowing of the whistle, and sees a great cloud, may think himself the witness of a wreck. All these phenomena, moreover, reveal us things as we have been in the habit of seeing them. I repeat, here also, that the photographic apparatus, in so far as it does not possess a refracting lens, shows things much more truly than our eye, which is always corrected by our memory. If I permit a man sitting on a chair to be photographed, front view, with his legs crossed and stretched far out, the result is a ludicrous picture because the boots seem immensely larger than the head of the subject. But the photograph is not at fault, for if the subject is kept in the same position and then the apparent size of head and boot are measured, we get accurately the same relation as on the photograph. We know by experience how big a head is. And hence, we ordinarily see all relations of size in proper proportion. But on the photograph we can not apply this "natural" standard because it is not given in nature, and we blame the camera.

If, in a criminal case, we are dealing with a description of size, and it is given as it is known from experience, not as it really appears, then if experience has deceived us, our testimony is also wrong, although we pretend to have testified on the basis of direct sense-perception.

The matter of after-images, probably because of their short duration, is of no criminalistic importance. I did once believe that they might be of considerable influence on the perception of witnesses, but I have not succeeded in discovering a single example in which this influence is perceptible.

On the other hand, the phenomenon of irradiation, the appearance of dark bodies as covered with rays of light by adjacent luminosities,

is of importance. This phenomenon is well-known, as are Helmholtz's and Plateau's explanations of it. But it is not sufficiently applied. One needs only to set a white square upon the blackest possible ground and at the same time a similar black square of equal size on a white ground, and then to place them under a high light, to perceive how much larger the white square appears to be. That such phenomena often occur in nature need not be expounded. Whenever we are dealing with questions of size it is indubitably necessary to consider the color of the object and its environment with respect to its background and to the resulting irradiation.