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.[310] 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[311] 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,[312] “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.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
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[313] 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.
[Illustration: FIG. 3.]
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.
[Illustration: FIG. 4.]
[Illustration: FIG. 5.]
[Illustration: FIG. 6.]
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.
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
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.
[Illustration: FIG. 9.]
[Illustration: FIG. 10.]
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.[314] 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,[315] 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[316] tells of color-illusions following upon insignificant
indigestion; Foderè of hysterics who see everything reversed, and
Hoppe[317] 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.[318] 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[319] 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 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.
[Illustration: FIG. 11.]
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 emphasising 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.