Concerning color vision only a few facts will be mentioned: 1. It will
be worth while, first of all, to consider whether color exists. Liebmann
holds that if all the people were blind to red, red would not exist;
red, i.e., is some cervical phantasy. So are light, sound, warmth,
taste, etc. With other senses we have another world. According to
Helmholtz, it is senseless to ask whether cinnabar is red as we see it
or is only so as an optical illusion. “The sensation of red is the
normal reaction of normally constructed eyes to light reflected from
cinnabar. A person blind to red, will see cinnabar as black, or a dark
grayish yellow, and this is the correct reaction for these abnormal
eyes. But he needs to know that his eyes are different from those of
other people. In itself the sensation is neither more correct nor less
correct than any other even though those who can see red are in the
great majority. The red color of cinnabar exists as such only in so far
as there are eyes which are similar to those of the majority of mankind.
As such light reflected from cinnabar may not properly be called red; it
is red only for especial kinds of eyes.” This is so unconditionally
incorrect that an impartial judge of photography says[179] that
everything that normal eyes call violet and blue, is very bright, and
everything they call green and red is very dark. The red-blind person
will see as equal certain natural reds, greens and gray-yellows, both in
intensity and shadow. But on the photograph he will be able to
distinguish the differences in brightness caused by these three
otherwise identical colors. We may, therefore, assume that colors
possess _objective_ differences, and that these objective differences
are perceived even by persons of normal vision. But whether I am able to
sense the same effect in red that another senses, and whether I should
not call red blue, if I had the color-vision of another, is as
impossible to discover as it is useless. When the question of color is
raised, therefore, we will try to discover only whether the person in
question has normal color-vision, or what the nature and degree of his
abnormality may be.
2. It is not unimportant to know whether single tints are recognizable
in the distance. There have been several examinations of this fact.
Aubert[180] constructed double squares of ten millimeters and determined
the angle of vision at which the color as such could be seen. His
results were:
+----------------+------------+------------+
| COLOR OF THE | WHITE | BLACK |
| SQUARE | BACKGROUND | |
+----------------+------------+------------+
| White | | 39´´ |
| Red | 1´ 43´´ | 59´´ |
| Light Green | 1´ 54´´ | 1´ 49´´ |
| Dirty Red | 3´ 27´´ | 1´ 23´´ |
| Blue | 5´ 43´´ | 4´ 17´´ |
| Brown | 4´ 55´´ | 1´ 23´´ |
| Light Blue | 2´ 17´´ | 1´ 23´´ |
| Orange | 1´ 8´´ | 0´ 39´´ |
| Gray | 4´ 17´´ | 1´ 23´´ |
| Rose | 2´ 18´´ | 3´ 49´´ |
| Yellow | 3´ 27´´ | 0´ 39´´ |
+----------------+------------+------------+
It is interesting to notice that the angle for blue on a white
background is almost nine times that for white, orange, or yellow on a
black background. In cases where colors are of importance, therefore, it
will be necessary to discover the color and the nature of its background
before the accuracy of the witness can be established.
3. It is well known that in the diminution of brightnesses red
disappears before blue, and that at night, when all colors have
disappeared, the blue of heaven is still visible. So if anybody asserts
that he has been able to see the blue of a man’s coat but not his
red-brown trousers, his statement is possibly true, while the converse
would be untrue. But there are no reliable or consonant accounts of the
order in which colors disappear in increasing darkness. The knowledge of
this order would help a great deal in the administration of criminal
justice.
4. The retina will not see red at the periphery, because there are no
red rods there. A stick of red sealing wax drawn across the eye from
right to left, appears at the periphery of the visual field to be black.
If, then, a witness has not looked right at a definitely red object, and
has seen it askance, he has certainly not observed its color. The
experiment may be made by anybody.
5. According to Quantz[181] objects in less refractable colors (red,
orange, yellow, and purple) look 0.2 to 3.6% bigger against white, while
blue, blue-green, and violet objects appear from 0.2 to 2.2% smaller.
Dark and long-lined objects seem longer; bright and horizontal seem
wider. And these facts are significant when witnesses judge of size.
6. If colors are observed through small openings, especially through
very small holes, the nuances become essentially different and green may
even seem colorless.
7. According to Aubert, sparkle consists of the fact that one point in a
body is very bright while the brightness diminishes almost absolutely
from that point; e.g., a glancing wire has a very narrow bright line
with deep shadows on each side; a ball of mercury in a thermometer, a
shining point and then deep shadow. When we see this we say it sparkles
because we unite it with a number of similar observations. It is
therefore conceivable that at a great distance, under conditions of
sharp or accidental illuminations, etc., we are likely to see things as
sparkling which do not do so in the least. With the concept “sparkling,”
moreover, we tend to unite, at least under certain circumstances,
definite images, and hence “glancing weapons” are often seen in places
where there were only quite harmless dull objects. So also coins are
seen to sparkle where really there are none.