Examples of colour blindness have been brought to your notice, and
various measurements made by persons possessing normal and defective
colour vision have been recorded, but no attempt has been made to
discuss the two leading rival theories that have been laid before you.
Regarding these theories you may expect me to say something, and to
avow myself a partisan of one or the other. This last I must decline
to do, though it will have been seen by the line that I have taken in
these lectures that the Young theory attracts me. There are, however,
difficulties in adapting it to explain several facts of colour vision
which seem to render it, to say the least, incomplete. For instance,
to explain the colours produced by simultaneous contrast, the Young
theory has to betake itself into psychological ground. I will show
you some excellent examples of contrast colours. We have upon the
screen a patch of white reflected light, superposed over a patch of
red light. Placing a thin rod in the paths of the two beams, we have
two shadows--one illuminated by white and the other by red, and lying
between them a mixed light of red and white. The shadow illuminated by
the white does not appear white, but a bluish-grey. When the spectrum
colour is changed to orange the blue is intensified, whilst when it is
green, what should be white appears of an orange-salmon colour. Other
colours give the white different hues which I need not describe.
These contrast colours are usually said to be _complementary_ to the
spectrum colours employed, though it must be recollected that what a
complementary colour should be is determined by the quality of the
white light which the two, when mixed, are made to match. But recent
measures of my own show that they are not truly complementary in most
instances, whatever the white light may be. But whether they are or not
does not much matter when the explanation offered by the followers of
the Young theory is considered, for it is asserted that such contrast
colours have no real existence, but are psychological, or--what this
comes to be--simply delusions. If they are not real colours felt by
the retina, they have a very good resemblance to them, and the same
series of delusions are so persistent and so constant for all normal
vision that they can always be measured as having a constant value. I
bear in mind the experiment in which the contrast colour, after being
produced, is isolated in the eye from the colour producing it and the
background, and the continuance of the hue produced by the contrast.
This _retention_ may be psychological, but there are no grounds to my
mind for saying that its _production_ is due to the same cause, more
especially as experiments have been arranged to show that one eye may
see a contrast colour, whilst the other may see it of its uncontrasted
hue. In this last experiment it can scarcely be conceived that one eye
should be subject to delusion, whilst the other was free from it. If,
then, we may presume that they are real colours, the Young theory fails
to explain them, and the explanation offered by the Hering theory is
much more acceptable, as it propounds the idea that the retina has to
be considered as a whole, and that if (say) red light is at work at one
part its complementary colour (blue-green) must be felt at another.
It would be still more acceptable had it happened that the contrast
colours were truly complementary, and if the same action was noticeable
when the adjacent part of the retina was not also stimulated.
For what I may call the straightforward part of colour vision, dealing
with ordinarily bright colours, the Young theory is amply sufficient;
but when we come to the feeble luminosities and the colour fields,
it is again difficult to adapt to explain the phenomena observed.
When we reduce the luminosity of a coloured ray sufficiently we feel
the sensation of grey light: no colour is felt. Why is this? On the
Hering theory it is capable of the explanation that we have the white
sensation left unextinguished, but I fail to see any explanation on
the Young theory. When we take colour fields with pure colours (see
appendix, page 208), we are met with the unexplained difficulty that
the colour from a bright spot of light vanishes almost suddenly towards
the periphery of the retina, and is replaced by a bright _white_ light,
and that the extent of the field depends on the brightness of the
colour. This, perhaps, is the most telling observation which can be
recorded against the Young theory as it stands at present. It has this
support, however, in the _sequence_ of the phenomena observed, viz.,
when the boundary for the colour which we will suppose to be pure red
is being taken (as described at page 11), that close to the point where
it bursts into pure white, it assumes a pink colour (_i.e._, a mixture
of red and white), whilst, if the red be scarlet, containing according
to this theory a little green sensation, it becomes orange before
white, showing that the red sensation is dimmed slightly before the
green, and so with the other colours. What are called “after images”
I have not touched upon so far, nor shall I here, for it is at this
point that we step into very debateable ground. The colours perceived
in them are, as yet, not capable of being put to the test of physical
measurement, and I must leave the psychologist or the physiologist to
account for them in their own way.
Viewing the Hering theory from a physical standpoint, and in the light
of colour measurement, it appears to be deficient in several respects.
To take one point. We have seen that when blue and yellow are mixed
together to make white the sum of the luminosities of the two colours
separately is equal to the luminosity of the white produced. According
to the Hering theory, the yellow colour contains a certain amount
of the white-black sensation besides the yellow sensation, as does
also the blue colour besides the blue sensation. The theory tells us
that when white is produced by the mixture, the blue sensation undoes
the work that the yellow sensation has done, and the white sensation
is alone left behind. If this be the case, the sum of the separate
luminosities cannot be the same as that of the white produced, but
should be greater. The theory also has to be strained sometimes to make
it fit in with other observed facts. Take, for instance, the case of
persons who are called red-blind and green-blind on the Young theory.
We are told by the Hering theory that both are red-green-blind--that
is, blind to both green and red, and only see blue and yellow--and that
the only difference between them is that the former has his spectrum
slightly shortened at the red end, the maxima of the yellow-blue
sensations being shifted a little further towards the violet end of the
spectrum. The natural question to ask is: Why this shift occurs? Surely
it is more rational to adopt a theory which does not require such a
supposition? If the sensitive matter acted upon by the yellow-blue
rays be always of the same chemical composition, the shift cannot
occur. It might, perhaps, be allowed that one shift was practicable,
but, unfortunately, the shifts must become numerous when the cases
of partial colour blindness are to be accounted for, and this would
necessitate a constantly varying chemical composition of this matter,
and of that acted upon by the red-green rays.
Again, in the extinction of the spectrum, the red and the green
sensations in quantities to neutralize one another should be
extinguished nearly together, even allowing for what physiologists
tell us is the case, that the breaking down, or dissimulation, of cell
tissue continues longer than its building up, but we find a large
difference between the two. As already indicated, the luminosity curve
of the feeble spectrum favours the theory of Hering being that here
we only have the white-black sensation, and naturally the persistency
curves must be scored in its favour. But the cases of B. C. and M.,
it seems to me, cannot be explained by the theory without any undue
straining or assumptions. If we try and fit the cases of colour
blindness due to tobacco scotoma to the theory, we find that in many
cases yellow is not recognised, though blue is invariably. If the blue
be active, the yellow should also be so.
And here I may remark that it has been assumed that the two classes
of colour blindness are due to different causes. A question to ask
ourselves is whether all colour blindness may not have been caused
originally by disease. In the congenital form, it is true, no disease
of the retina is traceable in the eye, and it is usually hereditary,
but it does not follow that the want of response of the perceiving
apparatus to certain sensations may not have been due to what, for want
of a better expression, I may call an hereditary partial paralysis
of the perceiving apparatus. If this be so, we have a connecting link
between the two classes, and then a perfect theory should explain both
classes on the same grounds. The suspicion that the monochromatic
vision of P. and Q. might possibly be due to disease before birth,
owing to the behaviour of their eyes under certain conditions, would
then be explicable. I have no desire to press this view, though it
seems to me to be one which is not out of all reason, taking analogies
from other defects which are hereditary.
It has been usually accepted that the fields for blue and yellow in
the eye are approximately the same, as are those of the green and red,
and this has been taken as showing the interdependence between the
two pairs according to the Hering theory. It has already been pointed
out that the question of extent of fields requires still further
investigation beyond that which it has received, and measures made by
the method given on page 208 seem to cast a doubt as to whether this
interdependence can be upheld. It will be noticed that the fields
do not extend proportionately on the nasal and temporal sides (see
also Fig. 3). It should also be remarked that the order of extent of
field for the different colours does not follow the same order as
their disappearance. A point that is sometimes raised in favour of
Hering’s theory is the negative image formed after the eye is fatigued
by looking at bright red or bright green. The negative images (see
page 30) are said to be the complementary of these colours. The Young
theory tells us that the red or the green sensation suffers fatigue
by one or other colour, and that when the eye subsequently rests on a
grey surface the other two sensations are chiefly stimulated and cause
the complementary colour. It is said that it is easier to produce a
_negative green_ image than a _negative red_ image, and the adherents
of Hering tell us that this is due to the fact that destructive action
is more readily carried out than constructive. In the Young theory, it
is held that the green sensation is always mixed with white, whilst
the red is fairly pure, and thus, for equal luminosities, the surplus
green sensation is much less stimulated than the red, which offers a
consistent explanation of this fact. There are several other minor
difficulties in the way of accepting Hering’s theory as it stands from
a physical point of view, but we need not discuss them now.
The final sensation curves for the spectrum colours on the Young theory
are still under consideration, and are not definitely fixed, though
the observations made have been very numerous. Recently Helmholtz, in
the last edition of his “Physiological Optics,” has calculated, from
Kœnig’s observations, that no one of the three sensations is singly
stimulated by any colour, even at the extreme ends of the spectrum, and
he makes the three fundamental sensations vary considerably from those
given in these pages. Every colour he states is considerably mixed with
white light. The calculations by which he arrived at this conclusion
are of a complicated nature, and I think if he had had besides the
colour equations of Kœnig, the luminosities and the extinction measures
before him, there might have been a modification of his views, for
these last give evidence to the contrary.
There is a possible modification of the Young theory which would
account for a good many of the phenomena that are unaccounted for by
it in its present form, though it may raise new difficulties in the
minds of some. Let us suppose that each of the three sensations were
compounded of fundamental _light and of colour_ in fixed and definite
proportions, and not in the same proportion in each; and further that
the apparatus in the eye which was responsible for each sensation
had two functions, one of which was to respond to the fundamental
light sensation and the other to the colour. One essential difference
between this modification of the Young theory and that of Hering
is that, whilst in the latter the white sensation is a sensation
_distinct from the colour sensations_, in the former it is a _definite
part_ of them. The fact that the sensation of colour is lost before
the sensation of light is one of the greatest significance, and any
theory to be accepted must offer a reasonable explanation of it. If
the modification suggested be made, it accounts for the existence
of this residuum of light equally as well as Hering’s theory, and
without its drawback. It is not hard to imagine the apparatus which
gives rise to two sensations, on the assumption of different kinds of
atomic motion, induced by the ether motion, or at least three kinds are
possible. When extinction of _colour_ is made, the ether vibrations
would have sufficient energy to induce but one kind of motion; and
when all _light_ was extinguished from the same ray, they would not
be capable of inducing any sensible motion whatever. In the case of
Miss W., who saw all colours as white, it might be that disease had
entirely prevented the first kind of motion in all three sensations,
and that in P. and Q. the red and green sensations were absent or
paralysed in their entirety, whilst the blue sensation was left in full
operation. In B. C. the blue and red sensations would be similarly
absent, leaving the green sensation unchanged. The coincidence of
their persistency and luminosity curves would then indicate that
the proportions of fundamental light and colour remained the same
throughout. Other examples and considerations seem to indicate that
the proportion of colour to fundamental light is greatest in the red
sensation, next in the green, and least in the blue. This would explain
why with increasing intensities blue appears white sooner than green,
and much sooner than red. The proposed modification would also offer
the necessary explanation as to the disappearance of colour from the
field.
Looking at colour vision from what I may call an evolutionary point
of view, the “light-colour” theory commends itself as probable. There
are many reasons for thinking that the visual sensation first evolved
was that of light, subsequently followed by that of colour. The first
evolved colour sensation would appear to have been the blue, and
the last the red. The discussion of this hypothesis would carry me
beyond my limits, and I must leave it thus baldly expressed for your
consideration.
For my own part, whatever theory of colour sensations may prove to
be the right one, I lean strongly to the idea that the cause of
vision will be found in chemical action, induced by the impact of
the different wave-lengths of light falling on sensitive matter. A
white substance may absorb all the wave-lengths found in the spectrum,
and if it have three sets of molecules, one of which has an atom or
atoms vibrating with the same period as the waves of light which show
a maximum for one sensation and another for another, and so on, the
requirements for the colour sensations are met. It may be that the
sensitive part of the retina is like a photographic plate, but with
this essential difference--that the sensitive material is constantly
changing. A photographic plate receives an impression which is not
recognisable by the eye, though it can be shown that a change in the
material does take place during the impact of light, by electrical and
other means. When the eye receives an impression of light, Dewar has
shown that in this case also a current of electricity is generated.
Recent published experiments of my own have demonstrated that with
a low intensity of light, the chemical change that occurs in a
photographic salt is by no means proportionate to that which takes
place with a greater intensity. In the eye, too, there is a limit of
sensibility to very feeble light. Again, the curves of the stimulation
of the colour sensations to the spectrum are closely of the same form
as the curves of sensitiveness of the various sensitive salts used by
photographers. These are analogies and, of course, must not be pressed
too far. There must be such a complexity in the sensitive material
in the eye, both chemical and physiological, that it may be that the
changes induced by light on the sensitive surface of the retina have
to be considered from both aspects. The purely chemical change is
naturally that to which a physicist is most prone to incline, and his
bias must be discounted, as must also that of the physiologist.
APPENDIX.
The following is extracted from Maxwell’s paper.
The following table contains the means of four sets of observations by
the same observer (K.):--
TABLE IV. (K.)
44·3 (20) + 31·0 (44) + 27·7 (68) = W.
16·1 (28) + 25·6 (44) + 30·6 (68) = W.
22·0 (32) + 12·1 (44) + 30·6 (68) = W.
6·4 (24) + 25·2 (36) + 31·3 (68) = W.
15·3 (24) + 26·0 (40) + 30·7 (68) = W.
19·8 (24) + 35·0 (46) + 30·2 (68) = W.
21·2 (24) + 41·4 (48) + 27·0 (68) = W.
22·0 (24) + 62·0 (52) + 13·0 (68) = W.
21·7 (24) + 10·4 (44) + 61·7 (56) = W.
20·5 (24) + 23·7 (44) + 40·5 (60) = W.
19·7 (24) + 30·3 (44) + 33·7 (64) = W.
18·0 (24) + 31·2 (44) + 32·3 (72) = W.
17·5 (24) + 30·7 (44) + 44·0 (76) = W.
18·3 (24) + 33·2 (44) + 63·7 (80) = W.
X.--REDUCTION OF THE OBSERVATIONS.
By eliminating W from the equations above by means of the standard
equation, we obtain equations involving each of the fourteen selected
colours of the spectrum, along with the three standard colours; and by
transposing the selected colour to one side of the equation, we obtain
its value in terms of the three standards. If any of the terms of these
equations are negative, the equation has no physical interpretation as
it stands; but by transposing the negative term to the other side it
becomes positive, and then the equation may be verified.
The following table contains the values of the fourteen selected tints
in terms of the standards. To avoid repetition, the symbols of the
standard colours are placed at the head of each column:--
TABLE VI.
Observer (K.) (24) (44) (68)
44·3 (20) = 18·6 + 0·4 + 2·8
16·1 (28) = 18·6 + 5·8 - 0·1
22·0 (32) = 18·6 + 19·3 - 0·1
25·2 (36) = 12·2 + 31·4 - 0·8
26·0 (40) = 3·3 + 31·4 - 0·2
35·0 (46) = - 1·2 + 31·4 + 0·3
41·4 (48) = - 2·6 + 31·4 + 3·5
62·0 (52) = - 3·4 + 31·4 + 17·5
61·7 (56) = - 3·1 + 21·0 + 30·5
40·5 (60) = - 1·9 + 7·7 + 30·5
33·7 (64) = - 1·1 + 1·1 + 30·5
32·3 (72) = + 0·6 + 0·2 + 30·5
44·0 (76) = + 1·1 + 0·7 + 30·5
63·7 (80) = + 0·3 - 1·8 + 30·5
Mr. James Simpson, formerly student of Natural Philosophy in my class,
has furnished me with thirty-three observations taken in good sunlight.
Ten of these were between the two standard colours, and give the
following result:--
33·7 (88) + 33·1 (68) = W.
The mean errors of these observations were as follows:--
Error of (88) = 2·5; of (68) = 2·3; of (88) + (68)
= 4·8; of (88) - (68) = 1·3.
The fact that the mean error of the sum was so much greater than the
mean error of the difference, indicates that in this case, as in all
others that I have examined, observations of equality of tint can be
depended on much more than observations of equality of illumination or
brightness.
From six observations of my own, made at the same time, I have deduced
the “trichromic” equation--
22·6 (104) + 26 (88) + 37·4 (68) = W (2)
If we suppose that the light which reached the organ of vision was the
same in both cases, we may combine these equations by subtraction, and
so find
22·6 (104) - 7·7 (88) + 4·3 (68) = D (3)
where D is that colour, the absence of the sensation of which
constitutes the defect of the dichromic eye.
The sensation which I have in addition to those of the dichromic eye
is therefore similar to the full red (104), but different from it in
that the red (104) has 7·7 of green (88) in it which must be removed,
and 4·3 of blue (68) substituted. This agrees pretty well with the
colour which Mr. Pole[A] describes as neutral to him, though crimson
to others. It must be remembered, however, that different persons of
ordinary vision require different proportions of the standard colours,
probably owing to differences in the absorptive powers of the media of
the eye, and that the above equation (2), if observed by K., would have
been
23 (104) + 32 (88) + 31 (68) = W (4)
and the value of D, as deduced from these observers, would have been
23 (104) - 1·7 (88) - 1·1 (68) = D (5)
in which the defective sensation is much nearer to the red of the
spectrum. It is probably a colour to which the extreme red of the
spectrum tends, and which differs from the extreme red only in not
containing that small proportion of “yellow” light which renders it
visible to the colour blind.
[A] Philosophical Transactions, 1859, Part I., p. 329.
From other observations by Mr. Simpson the following results have been
deduced:--
TABLE A.
(88) (68) | (88) (68)
(99·2 +) = 33·7 1·9 | 100 (96) = 108 7
31·3 (96) = 33·7 2·1 | 100 (92) = 120 5
28 (92) = 33·7 1·4 | 100 (88) = 100 0
33·7 (88) = 33·7 0 | 100 (84) = 61 11
54·7 (84) = 33·7 6·1 | 100 (82) = 47 21
71 (82) = 33·7 15·1 | 100 (80) = 34 33
99 (80) = 33·7 33·1 | 100 (78) = 22 47
70 (78) = 15·7 33·1 | 100 (76) = 10 59
56 (76) = 5·7 33·1 | 100 (72) = 1 92
36 (72) = 0·3 33·1 | 100 (68) = 0 100
33·1 (68) = 0 33·1 | 100 (64) = 0 83
40 (64) = 0·2 33·1 | 100 (60) = 3 60
55·5 (60) = 1·7 33·1 |
(57 -) = 0·3 33·1 |
In the table on the left side (99·2 +) means the whole of the spectrum
beyond (99·2) on the scale, and (57 -) means the whole beyond (57) on
the scale. The position of the fixed lines with reference to the scale
was as follows:--
A, 116; a, 112; B, 110; C, 106; D, 98·3; E, 88; F, 79; G, 61; H, 44.
The values of the standard colours in different parts of the spectrum
are given on the right side of the above table, and are represented by
the curves of Fig. 9, Plate II., where the left-hand curve represents
the intensity of the “yellow” element, and the right-hand curve that of
the “blue” element of colour as it appears to the colour blind.
The appearance of the spectrum to the colour blind is as follows:--
From A to E the colour is pure “yellow,” very faint up to D, and
reaching a maximum between D and E. From E to one-third beyond F
towards G the colour is mixed, varying from “yellow” to “blue,” and
becoming neutral or “white” at a point near F. In this part of the
spectrum the total intensity, as given by the dotted line, is decidedly
less than on either side of it, and near the line F, the retina close
to the “yellow spot” is less sensible to light than the parts further
from the axis of the eye. This peculiarity of the light near F is even
more marked in the colour blind than in the ordinary eye. Beyond F the
“blue” element comes to a maximum between F and G, and then diminishes
towards H, the spectrum from this maximum to the end being pure “blue.”
The results given above were all obtained with the light of white
paper, placed in clear sunshine. I have obtained similar results when
the sun was hidden, by using the light of uniformly illuminated clouds,
but I do not consider these observations sufficiently free from
disturbing circumstances to be employed in calculation. It is easy,
however, by means of such observations, to verify the most remarkable
phenomena of colour blindness, as, for instance, that the colours
from red to green appear to differ only in brightness, and that the
brightness may be made identical by changing the width of the slit;
that the colour near F is a neutral tint, and that the eye in viewing
it sees a dark spot in the direction of the axis of vision; that the
colours beyond are all blue of different intensities, and that any
“blue” may be combined with any “yellow” in such proportions as to
form “white.” These results I have verified by the observations of
another colour-blind gentleman, who did not obtain sunlight for his
observations; and as I have now the means of carrying the requisite
apparatus easily, I hope to meet with other colour-blind observers, and
to obtain their observations under more favourable circumstances.
MEASUREMENTS OF COLOUR FIELDS.
Some experiments in the measurement of the colour fields in the
horizontal direction with the pure spectrum colours will help to show
what importance is to be attached to the luminosity of the colour and
the size of the spot of light with which the observations are made. A
yellow and a blue of the spectrum were taken of such hues that when
mixed they formed a patch of white light similar to the electric light.
Their luminosities were measured, and the yellow found to be 1·6 of the
light of an amyl-acetate lamp or 1·28 standard candles; the blue was
1/24 of this luminosity. The fields for these two colours were measured
by automatically throwing spots of each colour separately on a white
card which moved round a centre over which the eye was placed. The
light was subsequently diminished to ½, ¼, and ⅛ of the above values,
and readings again made. The following results were obtained with a
spot of ·7 inch diameter:--
Yellow. Blue.
Light. -------------------------- ---------------------------
Nasal side. Temporal side. Nasal side. Temporal side.
Full 33° 45° 35° 45°
½ 24° 36° 26° 38°
¼ 18° 24° 22° 32°
⅛ 11° 15° 19° 30°
With a spot of ·3 inch diameter the following were obtained:--
Full 24° 32° 21° 27°
½ 17° 28° 16° 22°
¼ 13° 16° 14° 20°
⅛ 8° 10° 13° 16°
It will be evident how the field contracts as the light is diminished
in brightness, and also that the blue field does not diminish equally
with the yellow field, but is more persistent. Again, it will be
noticed that the luminosity of the blue, for the same extent of field
to be covered, has to be much lower than for the yellow.
The diminished area of the spot of light also diminishes the field, and
the same order of diminution of field is obtained as with the larger
spot.
Another set of experiments, made with the same aperture of slit passed
through the spectrum, and the field taken at different points, give the
following results:--
Spectrum scale. Nasal side. Temporal side.
(See Fig. 41,
page 210.)
58·6 18° 35°
54·6 27° 46°
50·6 33° 47°
46·6 25° 30°
42·6 21° 21°
38·6 17° 17°
34·6 22° 30°
30·6 25° 33°
26·6 33° 40°
22·6 37° 44°
18·6 28° 40°
14·6 22° 34°
8·6 20° 30°
Here we see that although the luminosity of the colour spots varies
at the spectrum luminosity, the fields do not vary proportionally;
when the luminosities of the green, yellow and red are made equal, the
fields become nearly equal on the nasal side. The field for the blue,
however, then becomes vastly larger than that for the others, showing a
peculiarity which is very remarkable.
[Illustration: FIG. 41.
_Spectrum Scale._]
Recently published experiments on colour fields have been so largely
based on the exigencies of the Hering theory, that it is somewhat
difficult to decide their significance from any other aspect.
TABLE I.--LUMINOSITY CURVES FOR THE NORMAL EYE (see Fig. 20).
-------+--------------+----------------+--------------+-----------
I. | II. | III. | IV. | V.
-------+--------------+----------------+--------------+-----------
Scale | Wave-length. | Outside yellow | Yellow spot. | Fovea
number.| | spot. | | centralis.
-------+--------------+----------------+--------------+-----------
64 | 7217 | | |
63 | 7082 | .. | 1 |
62 | 6957 | 1 | 2 | 2
61 | 6839 | 2 | 4 | 4
60 | 6728 | 3·5 | 7 | 8
59 | 6621 | 7·5 | 12·5 | 15·5
58 | 6520 | 12·5 | 21 | 24
57 | 6423 | 19 | 33 | 37·5
56 | 6330 | 27·5 | 50 | 60
55 | 6242 | 35 | 65 | 77
54 | 6152 | 43 | 80 | 90
53 | 6074 | 52·5 | 90 | 97
52 | 5996 | 61·0 | 96 | 100
51 | 5919 | 71·0 | 99 | 100
50 | 5850 | 79·0 | 100 | 98
49 | 5783 | 84 | 99 | 95
48 | 5720 | 85 | 97 | 90
47 | 5658 | 83·5 | 92·5 | 85
46 | 5596 | 81·0 | 87 | 79
45 | 5538 | 77·0 | 81 | 72·5
44 | 5481 | 72.5 | 75 | 66
43 | 5427 | 68·0 | 69 | 59
42 | 5373 | 62·5 | 62·5 | 51
41 | 5321 | 57 | 57 | 45
40 | 5270 | 52 | 50 | 40
39 | 5221 | 46 | 42·5 | 32
38 | 5172 | 41·5 | 36 | 27·5
37 | 5128 | 37·5 | 29·5 | 22·0
36 | 5085 | 33·5 | 24 | 18
35 | 5043 | 30·0 | 18·2 | 14
34 | 5002 | 26·5 | 14·2 | 10
33 | 4963 | 24 | 10·5 | 8·4
32 | 4924 | 21 | 8·5 | 6·5
31 | 4885 | 18·5 | 7·0 | 5·5
30 | 4848 | 16·5 | 5·5 | 4·0
29 | 4812 | 14·5 | 4·7 | 3·5
28 | 4776 | 13·0 | 4·0 | 3·0
27 | 4742 | 11·5 | 3·5 | 2·0
26 | 4707 | 10·5 | 2·8 | 2·4
25 | 4675 | 9·4 | 2·3 | 2·1
24 | 4639 | 8·2 | 1·82 | 1·9
23 | 4608 | 7·3 | 1·6 | 1·5
22 | 4578 | 6·3 | 1·4 |
21 | 4548 | 5·7 | 1·2 |
20 | 4517 | 5·0 | 1·08 | 1·0
19 | 4488 | 4·5 | ·94 |
18 | 4459 | 4·0 | ·86 |
17 | 4437 | 3·6 | ·78 |
16 | 4404 | 3·1 | ·70 |
15 | 4377 | 2·7 | ·62 | ·62
14 | 4349 | 2·3 | ·56 |
13 | 4323 | 2·1 | ·50 |
12 | 4296 | 1·9 | ·45 |
11 | 4271 | 1·65 | ·40 |
10 | 4245 | 1·4 | ·34 |
9 | 4221 | 1·2 | ·30 |
8 | 4197 | 1·0 | ·26 |
7 | 4174 | ·88 | ·22 |
6 | 4151 | ·75 | ·18 |
5 | 4131 | ·63 | ·16 |
4 | 4106 | ·50 | ·14 |
-------+--------------+----------------+--------------+-----------
TABLES II. AND III.--CURVES OF LUMINOSITY OF A PARTIALLY RED-BLIND AND
OF A PARTIALLY GREEN-BLIND PERSON (see Fig. 23).
-------------+------------+-----------------------
| | Luminosity.
Scale number.|Wave-length.+----------+------------
| |Red-blind.|Green-blind.
-------------+------------+----------+------------
64 | 7217 | 0 | 1
62 | 6957 | 1 | 2
60 | 6728 | 2 | 7
58 | 6520 | 6 | 21
56 | 6330 | 12 | 50
54 | 6152 | 26 | 80
52 | 5996 | 49 | 96
50 | 5850 | 70 | 98
48 | 5720 | 77 | 93
46 | 5596 | 77 | 83
44 | 5481 | 70 | 70
42 | 5373 | 61 | 55
40 | 5270 | 47 | 40
38 | 5172 | 34 | 27
36 | 5085 | 23 | 18
34 | 5002 | 14 | 10
32 | 4924 | 8·5 | 5·5
30 | 4848 | 5·5 | 3·0
28 | 4776 | 4·0 | 2·5
26 | 4707 | 2·7 | 2·0
24 | 4639 | 1·8 | 1·8
22 | 4578 | 1·35 | 1·4
20 | 4517 | 1·1 | 1·1
-------------+------------+----------+------------
TABLE IV.--LUMINOSITY OF SPECTRUM REDUCED IN INTENSITY, SO THAT D =
1/132·5 AMYL LAMP 1 FOOT DISTANT (see Fig. 25).
-------+---------+-----------+------------+---------------
| | Mean | | Persistency
| | reading, | P. and Q.’s| curve for the
Scale | Mean | reduced to| readings, | centre of
number.| reading.| 100 max. | 100 max. | the eye.
-------+---------+-----------+------------+---------------
55·6 | ·5 | ·6 | 2 | 2
53·6 | 5·5 | 7·0 | 3·6 | 3·6
51·6 | 13 | 16·7 | 8 | 8
49·6 | 23 | 29·7 | 22 | 22
47·6 | 40 | 50·0 | 44 | 44
45·6 | 57 | 71·2 | 69 | 69
43·6 | 70 | 87·5 | 93 | 93
41·6 | 79 | 98·7 | 100 | 99·5
39·6 | 78 | 97·5 | 99·5 | 98·5
37·6 | 74 | 92·5 | 96 | 93
35·6 | 66 | 82·5 | 89 | 84
33·6 | 55 | 68·7 | 77·5 | 71
31·6 | 44·5 | 55·2 | 61 | 53·5
29·6 | 35 | 43·7 | 45·5 | 36·5
27·6 | 24 | 30·0 | 33·5 | 24
25·6 | 17 | 21·7 | 25 | 16
23·6 | 13 | 16·7 | 18 | 10
21·6 | 10 | 12·5 | 13 | 8
19·6 | 8 | 10·0 | 9·5 | 6
13·6 | 3 | 3·7 | 4·2 | 3
9·6 | 2 | 2·5 | 2·5 | 2
-------+---------+-----------+------------+---------------
TABLE V.--LIMIT OF COLOUR VISION (see Fig. 26.).
--------+---------+---------------+------------+----------------
Scale | Wave- | Mean reading | Luminosity | Luminosity of
Number. | Length. | of the colour | of the | the rays when
| | limit of the | ordinary | each colour
| | spectrum D, | spectrum. | disappears,
| | being 1 amyl | | each ray having
| | lamp in | | the original
| | 1/10000ths. | | luminosity of
| | | | 1 amyl lamp
| | | | in 1/100000ths.
--------+---------+---------------+------------+----------------
61 | 6839 | 120 | 4 | 48·0
60 | 6728 | 67 | 7 | 46·9
58 | 6520 | 26 | 21 | 54·6
56 | 6330 | 13 | 50 | 65·0
54 | 6152 | 9·5 | 80 | 76·0
52 | 5996 | 9·0 | 96 | 86·4
50 | 5850 | 9·0 | 100 | 90·0
48 | 5720 | 9·0 | 97 | 87·3
44 | 5481 | 9·5 | 75 | 71·3
40 | 5270 | 10·5 | 50 | 52·5
36 | 5085 | 12·5 | 24 | 30·0
32 | 4924 | 18 | 8·5 | 15·3
28 | 4776 | 32 | 4·0 | 12·8
24 | 4639 | 55 | 1·8 | 12·0
20 | 4517 | 90 | 1·08 | 9·7
16 | 4404 | 160 | ·70 | 11·2
12 | 4296 | 250 | ·45 | 11·0
8 | 4197 | 400 | ·26 | 10·4
4 | 4106 | 700 | ·14 | 9·8
--------+---------+---------------+------------+----------------
TABLE VI.--EXTINCTION BY CENTRAL PORTION OF NORMAL EYE (see Fig. 28).
-------+------------+--------------+-----------+----------+-----------
I. | II. | III. | IV. | V. | VI.
-------+------------+--------------+-----------+----------+-----------
| | E. | L. | |Persistency
| | Reduction of | | | curve
| | original | Luminosity|(E × L) / | 650 / E
Scale |Wave-length.| luminosity | of | 100 |(Maximum =
number.| | in millionths| original | | 100).
| | to cause | beam. | |
| | extinction. | | |
-------+------------+--------------+-----------+----------+-----------
64 | 7217 | 55,000 | | |
63 | 7082 | 30,000 | 1 | 300·0 |
62 | 7957 | 15,000 | 2 | 300·0 |
61 | 6839 | 7500 | 4 | 300·0 |
60 | 6728 | 3750 | 7 | 262·5 |
59 | 6621 | 1900 | 12·5 | 237·5 | ·34
58 | 6520 | 1050 | 21 | 220·5 | ·62
57 | 6423 | 650 | 33 | 214·5 | 1·0
56 | 6333 | 380 | 50 | 190·0 | 1·71
55 | 6242 | 272 | 65 | 176·8 | 2·38
54 | 6152 | 196 | 80 | 156·0 | 3·32
53 | 6074 | 140 | 90 | 126·0 | 4·64
52 | 5996 | 97 | 96 | 93·12 | 6·70
51 | 5919 | 57 | 99 | 56·43 | 11·40
50 | 5850 | 35 | 100 | 35·0 | 18·6
49 | 5783 | 24 | 99 | 23·76 | 27·1
48 | 5720 | 17 | 97 | 16·49 | 38·2
47 | 5658 | 12·6 | 92·5 | 11·65 | 51·6
46 | 5596 | 10·2 | 87 | 8·87 | 63·7
45 | 5538 | 8·6 | 81 | 6·97 | 75·6
44 | 5481 | 7·4 | 75 | 5·55 | 87·8
43 | 5427 | 6·7 | 69 | 4·62 | 97·0
42 | 5373 | 6·55 | 62·5 | 4·09 | 99·5
41 | 5321 | 6·5 | 57 | 3·705 | 100
40 | 5270 | 6·55 | 50 | 3·27 | 98·5
39 | 5221 | 6·65 | 42·5 | 2·83 | 97·5
38 | 5172 | 6·85 | 36 | 2·46 | 95·0
37 | 5128 | 7·2 | 29·5 | 2·12 | 90·0
36 | 5085 | 7·6 | 24 | 1·82 | 81·3
35 | 5043 | 8·15 | 18·2 | 1·48 | 80·0
34 | 5002 | 8·8 | 14·2 | 1·25 | 74·0
33 | 4963 | 10·2 | 10·5 | 1·07 | 63·0
32 | 4924 | 11·6 | 8·5 | ·988 | 56·0
31 | 4885 | 13·6 | 7·0 | ·952 | 47·7
30 | 4848 | 16·3 | 5·5 | ·896 | 40·0
29 | 4812 | 20·5 | 4·7 | ·963 | 31·7
28 | 4776 | 26·0 | 4·0 | 1·040 | 25·0
27 | 4742 | 31·0 | 3·5 | 1·085 | 20·9
26 | 4707 | 38·5 | 2·8 | 1·078 | 16·9
25 | 4674 | 46·0 | 2·3 | 1·058 | 14·1
24 | 4639 | 56·0 | 1·82 | 1·019 | 11·6
23 | 4608 | 67·0 | 1·6 | 1·072 | 9·7
22 | 4578 | 80 | 1·4 | 1·120 | 8·41
21 | 4548 | 95 | 1·2 | 1·140 | 7·22
20 | 4517 | 107 | 1·08 | 1·156 | 6·1
19 | 4488 | 124 | ·94 | 1·165 | 5·23
18 | 4459 | 140 | ·86 | 1·204 | 4·64
17 | 4437 | 160 | ·78 | 1·228 | 4·1
16 | 4404 | 180 | ·70 | 1·260 | 3·60
15 | 4377 | 200 | ·62 | 1·240 | 3·25
14 | 4349 | 220 | ·56 | 1·232 | 2·95
13 | 4323 | 240 | ·50 | 1·200 | 2·7
12 | 4296 | 270 | ·45 | 1·215 | 2·4
11 | 4271 | 300 | ·40 | 1·200 | 2·18
10 | 4245 | 335 | ·34 | 1·139 | 1·94
9 | 4221 | 375 | ·30 | 1·125 | 1·73
8 | 4197 | 430 | ·26 | 1·118 | 1·51
7 | 4174 | 490 | ·22 | 1·078 | 1·32
6 | 4151 | 510 | ·18 | ·918 | 1·27
5 | 4131 | 640 | ·16 | 1·024 | 1·01
4 | 4106 | 750 | ·14 | 1·050 | 0·86
-------+------------+--------------+-----------+----------+-----------
TABLE VII.--EXTINCTION BY WHOLE EYE
(see Fig. 28).
--------+---------+--------------+------------+---------+------------
I. | II. | III. | IV. | V. | VI.
--------+---------+--------------+------------+---------+------------
Scale | Wave- | E. | L. |(E × L) /| Persistency
number. | length. | Reduction of | | 160 | curve
| | original | Luminosity | | 650 / E
| | luminosity | of | | (Maximum=
| | in millionths| original | | 100).
| | to cause | beam. | |
| | extinction. | | |
--------+---------+--------------+------------+---------+------------
38 | 5172 | 6·9 | 41·5 | 2·86 | 94·2
37 | 5128 | 7·1 | 37·5 | 2·66 | 91·6
36 | 5085 | 7·4 | 33·5 | 2·48 | 87·8
35 | 5043 | 7·7 | 30·0 | 2·31 | 84·4
34 | 5002 | 8·0 | 26·5 | 2·12 | 81·2
33 | 4963 | 8·4 | 24·0 | 2·02 | 77·5
32 | 4924 | 8·8 | 21·0 | 1·85 | 73·8
31 | 4885 | 9·4 | 18·5 | 1·74 | 69·2
30 | 4848 | 10·0 | 16·5 | 1·65 | 65·0
29 | 4812 | 10·7 | 14·5 | 1·55 | 60·6
28 | 4776 | 11·5 | 13·0 | 1·49 | 56·5
27 | 4742 | 13·0 | 11·5 | 1·49 | 50·0
26 | 4707 | 14·5 | 10·5 | 1·52 | 44·8
24 | 4639 | 18·5 | 8·2 | 1·52 | 34·1
22 | 4578 | 23·0 | 6·3 | 1·45 | 28·3
20 | 4517 | 30·0 | 5·0 | 1·50 | 21·7
18 | 4459 | 39·0 | 4·0 | 1·56 | 16·7
16 | 4404 | 51 | 3·1 | 1·59 | 12·3
14 | 4349 | 66 | 2·3 | 1·52 | 9·85
12 | 4296 | 80 | 1·9 | 1·52 | 8·12
10 | 4245 | 110 | 1·4 | 1·54 | 5·91
8 | 4197 | 154 | 1·0 | 1·54 | 4·22
6 | 4151 | 204 | ·75 | 1·54 | 3·18
4 | 4106 | 307 | ·5 | 1·54 | 2·11
2 | 4063 | 513 | ·3 | 1·54 | 1·26
0 | 4020 | 770 | ·2 | 1·54 | ·84
--------+---------+--------------+------------+---------+------------
From 38 to 64 the extinction is the same as with the central part of
the eye.
TABLE VIII.--P.’S CURVES[B] (see Fig. 31).
-------+--------+------------+------------+-------------+-----------+------------
I. | II. | III. | IV. | V. | VI. | VII.
-------+--------+------------+------------+-------------+-----------+------------
Scale | Wave- | Mean | Adopted | Persistency | P.’s | Absolute
number.| length.| reading of | reading in | curve | luminosity| luminosity
| | extinction | millionths | (680 / | curve. | of
| | in | of |ad. reading).| | extinction.
| | millionths | original | | | (IV.×VI.) /
| | of | luminosity.| | | 14
| | original | | | |
| | luminosity.| | | |
-------+--------+------------+------------+-------------+-----------+------------
52 | 5996 | 68 | 68 | 10 | 7 | 34
50 | 5850 | 35 | 35 | 19·4 | 19 | 47·5
48 | 5720 | 17 | 17 | 40 | 39 | 47·3
46 | 5596 | 10·2 | 10 | 68 | 65 | 46·4
45 | 5538 | 9·3 | 9·0 | 76 | 76 | 48·8
44 | 5481 | 8·0 | 8·1 | 84 | 90 | 52·8
42 | 5373 | 7·2 | 7·2 | 94·5 | 98 | 50·3
40 | 5270 | 6·7 | 6·8 | 100 | 99 | 48·1
38 | 5172 | 7·2 | 7·0 | 97 | 97·5 | 48·7
36 | 5085 | 8·05 | 7·7 | 90 | 90 | 49·5
34 | 5002 | 8·05 | 8·4 | 81 | 80 | 47·9
32 | 4924 | 9·9 | 9·8 | 69 | 65 | 45·5
30 | 4848 | 13·2 | 12·5 | 54 | 50 | 44·6
28 | 4776 | 13·9 | 15·0 | 45·3 | 36 | 38·6
27 | 4742 | 16·8 | 17·0 | 40 | 31·5 | 38·2
26 | 4707 | 21·6 | 20·5 | 32 | 26·5 | 38·8
24 | 4639 | 30 | 27 | 25 | 19·5 | 37·6
22 | 4578 | 36 | 35 | 19 | 14 | 35
20 | 4517 | 42 | 45 | 15·5 | 10 | 32·2
16 | 4404 | 79 | 79 | 8·5 | 5·5 | 31·2
10 | 4245 | 180 | 190 | 3·6 | 2·5 | 32·2
6 | 4151 | 270 | 270 | 2·7 | |
-------+--------+------------+------------+-------------+-----------+------------
[B] In this and the next two Tables the intensity of the
illumination of the D ray before reduction is equal to that
of an amyl-acetate lamp at one foot from a screen. The
figures in Col. VII. are in millionths of the illumination
of an amyl-acetate lamp at one foot distant, every ray
being made of that intensity.
TABLE IX.--H. R.’S CURVES (see Fig. 32).
-------+--------+------------+------------+-------------+-----------+------------
I. | II. | III. | IV. | V. | VI. | VII.
-------+--------+------------+------------+-------------+-----------+------------
Scale | Wave- | Mean | Adopted | Persistency | Luminosity| Absolute
number.| length.| reading of | reading in | curve | curve. | luminosity
| | extinction | millionths | (590 / | | of
| | in | of |ad. reading).| | extinction
| | millionths | original | | | (IV.×VI.) /
| | of | luminosity.| | | 48
| | original | | | |
| | luminosity.| | | |
-------+--------+------------+------------+-------------+-----------+------------
57 | 6423 | 1200 | 1200 | ·49 | 5 | 125
56 | 6330 | 900 | 850 | ·69 | 7 | 124
55 | 6242 | 500 | 550 | 1·07 | 10 | 115
54 | 6152 | 250 | 250 | 2·36 | 17 | 88
53 | 6074 | .. | 150 | 3·93 | 25 | 78
52 | 5996 | 90 | 90 | 6·56 | 35 | 66
51 | 5919 | 60 | 45 | 13·1 | 47 | 44
50 | 5850 | 27 | 27 | 21·8 | 57 | 32
48 | 5720 | 18 | 15 | 39·3 | 66 | 21
46 | 5596 | 10 | 10 | 59 | 69 | 14
44 | 5481 | 9·3 | 8 | 73·8 | 64 | 11
42 | 5373 | 6·5 | 6·2 | 95·1 | 56·5 | 7
40 | 5270 | 5·9 | 5·9 | 100 | 45 | 5·5
38 | 5172 | 6 | 6 | 98·3 | 32 | 4
36 | 5085 | .. | 6·6 | 89·4 | 20 | 2·7
35 | 5043 | 7 | 7·2 | 81·9 | 16 | 2·4
34 | 5002 | .. | 8 | 73·8 | 12·5 | 2·1
32 | 4924 | 10 | 9·6 | 61·5 | 8 | 1·6
30 | 4848 | 11·5 | 12 | 49·2 | 6 | 1·5
28 | 4776 | 14·5 | 14·5 | 40·7 | 5 | 1·5
26 | 4707 | 20 | 17·5 | 33·7 | 4 | 1·5
24 | 4639 | 20 | 22 | 26·8 | 3 | 1·4
22 | 4578 | .. | 30 | 19·7 | 2·4 | 1·5
18 | 4459 | 55 | 57 | 10·4 | 1·3 | 1·5
14 | 4349 | 115 | 115 | 5·1 | ·7 | 1·7
10 | 4245 | .. | 160 | 3·7 | ·5 | 1·7
6 | 4151 | 200 | 200 | 2·9 | ·4 | 1·7
-------+--------+------------+------------+-------------+-----------+------------
TABLE X.--V. H.’S CURVES (see Fig. 33).
-------+--------+------------+------------+-------------+-----------+------------
I. | II. | III. | IV. | V. | VI. | VII.
-------+--------+------------+------------+-------------+-----------+------------
Scale | Wave- | Mean | Adopted | Persistency | Luminosity| Absolute
number.| length.| reading of | reading in | curve | curve. | luminosity
| | extinction | millionths | (530 / | | of
| | in | of |ad. reading).| | extinction
| | millionths | original | | | (IV.×VI.) /
| | of | luminosity.| | | 75.
| | original | | | |
| | luminosity.| | | |
-------+--------+------------+------------+-------------+-----------+------------
57 | 6423 | 500 | 500 | 1·1 | 31 | 206
56 | 6330 | 350 | 350 | 1·5 | 43 | 200
54 | 6152 | 200 | 180 | 2·9 | 61 | 146·4
52 | 5996 | 100 | 100 | 5·3 | 70 | 93·3
50 | 5850 | 40 | 40 | 13·3 | 73 | 38·9
48 | 5720 | .. | 25 | 21·2 | 69 | 23
46 | 5596 | 10 | 10 | 53·0 | 63 | 8·4
45 | 5538 | 6·5 | 6·5 | 81·6 | 58 | 5·0
44 | 5481 | 6·0 | 5·7 | 93 | 54 | 4·1
42 | 5373 | 5·5 | 5·3 | 100 | 46 | 3·3
40 | 5270 | 5·5 | 5·4 | 98·2 | 36 | 2·6
38 | 5172 | 5·7 | 5·7 | 93 | 24 | 1·8
36 | 5085 | 6·7 | 6·5 | 81·6 | 15 | 1·3
34 | 5002 | 7·0 | 7·0 | 75·7 | 9·5 | ·89
32 | 4924 | 8·5 | 8·5 | 62·3 | 7·0 | ·79
30 | 4848 | 10·7 | 10·5 | 50·5 | 5·0 | ·70
28 | 4776 | 16 | 16 | 33·1 | 3·7 | ·79
26 | 4707 | .. | 22·5 | 23·5 | 2·7 | ·81
24 | 4639 | 30 | 31 | 17·1 | 1·82 | ·75
22 | 4578 | 42·5 | 42 | 12·6 | 1·4 | ·78
20 | 4517 | 55 | 55 | 9·6 | 1·0 | ·73
16 | 4404 | 105 | 100 | 5·3 | ·7 | ·93
12 | 4296 | 175 | 170 | 3·1 | ·45 | 1·02
10 | 4245 | 200 | 200 | 2·7 | ·34 | ·91
-------+--------+------------+------------+-------------+-----------+------------
TABLE XI.--B. C.’S CURVES (see Fig. 34).
--------+--------+-------------+------------+-----------+-------------
| | | | |
I. | II. | III. | IV. | V. | VI.
--------+--------+-------------+------------+-----------+-------------
Scale | Wave- | Adopted | Persistency| Luminosity| Absolute
Number. | length.| reading in | curve | of | luminosity
| | hundred | 12,500 | original | of
| | thousandths.| readings | beam. | extinction
| | | in V. | | III. and V.
--------+--------+-------------+------------+-----------+-------------
61 | 6839 | 7500 | 1·6 | |
60 | 6728 | 5500 | 2·3 | ·5 | 27·5
59 | 6622 | 4000 | 3·1 | 1 | 40
58 | 6520 | 2800 | 4·5 | 2 | 56
57 | 6423 | 2000 | 6·2 | 4 | 80
56 | 6330 | 1500 | 8·3 | 6 | 90
55 | 6242 | 1150 | 10·8 | 8 | 92
54 | 6152 | 950 | 13·1 | 11·5 | 109·2
53 | 6074 | 750 | 16·6 | 16 | 120
52 | 5996 | 580 | 21·6 | 21·5 | 125
51 | 5919 | 430 | 29 | 28·5 | 122·5
50 | 5850 | 350 | 36 | 37 | 129·5
49 | 5783 | 275 | 45·5 | 47 | 129·2
48 | 5720 | 215 | 58 | 60 | 129
47 | 5658 | 170 | 73·4 | 76 | 129·2
46 | 5596 | 140 | 89·3 | 92 | 129
45 | 5538 | 125 | 100 | 98 | 122·5
44 | 5481 | 125 | 100 | 100 | 125
43 | 5427 | 130 | 96·1 | 97 | 126
42 | 5373 | 150 | 83 | 85 | 127·5
41 | 5321 | 180 | 69·4 | 65 | 117
40 | 5270 | 215 | 59 | 45 | 96·7
39 | 5221 | 250 | 50 | 30 | 75
38 | 5172 | 290 | 43 | 1·5 | 723·2
37 | 5128 | 335 | 37 | 16 | 53·6
36 | 5055 | 380 | 33 | 11·5 | 43·7
34 | 5002 | 500 | 25 | 7 | 35
32 | 4994 | 650 | 19 | 4 | 26
30 | 4848 | 850 | 14 | 2·5 | 23·3
28 | 4776 | 1100 | 11·4 | 2 | 22
26 | 4707 | 1500 | 8·3 | 1·5 | 22
24 | 4639 | 2000 | 6·2 | 1 | 20
22 | 4578 | 2700 | 4·6 | 5 | 13·5
18 | 4459 | 4750 | | |
14 | 4349 | 7500 | | |
10 | 4245 | 11000 | | |
--------+--------+-------------+------------+-----------+-----------
TABLE XII.--M.’S LUMINOSITY CURVE COMPARED WITH THE NORMAL (see Fig.
30).
-------+--------+--------+-------+----------+-----------+----------
I. | II. | III. | IV. | V. | VI. | VII.
-------+--------+--------+-------+----------+-----------+----------
Scale | Wave- | Mean | Mean | Normal |Difference |
number.| length.|reading.|reading|luminosity|of last two|Difference
| | |× 1·8. | curve, | columns. | × 5·15.
| | | |centre of | |
| | | | eye. | |
-------+--------+--------+-------+----------+-----------+----------
61 | 6839 | 2 | 3·6 | 4 | ·4 | 2·57
59 | 6621 | 7 | 12·6 | 12·5 | -·1 | ·51
57 | 6423 | 18 | 32·4 | 33 | +·6 | 3·09
55 | 6242 | 36 | 64·8 | 65 | ·2 | 1·03
53 | 6074 | 49 | 88·2 | 89·5 | 1·3 | 6·71
52 | 5996 | 52 | 95·4 | 96·5 | 1·1 | 5·66
51 | 5919 | 54 | 97·2 | 99·5 | 2·3 | 11·8
50 | 5850 | 54 | 97·2 | 100 | 2·8 | 14·4
49 | 5782 | 52·5 | 94·5 | 99·5 | 5·0 | 25·7
48 | 5720 | 50 | 90 | 97 | 7·0 | 36·0
47 | 5658 | 46 | 82·8 | 92·5 | 9·7 | 49·9
46 | 5596 | 41 | 73·8 | 87 | 13·2 | 68·0
44 | 5481 | 32 | 57·6 | 75 | 17·4 | 89
42 | 5373 | 23 | 43·2 | 62.5 | 19·3 | 99
40 | 5270 | 17 | 30·6 | 50 | 19·4 | 100
38 | 5172 | 10 | 17·5 | 35·5 | 18 | 93
36 | 5085 | 4 | 7·2 | 24 | 16·8 | 86·5
34 | 5002 | 1·0 | 1·8 | 14·5 | 12·7 | 65·5
31 | 4885 | ·5 | ·7 | 6·5 | 5·8 | 37·7
28 | 4776 | 0 | 0 | 4 | 4 | 20·6
-------+--------+--------+-------+----------+-----------+----------
TABLE XIII.--MISS W.’S CURVES (see Fig. 39).
--------+---------+-----------+--------------+------------
Scale | Wave- | Readings. | Extinction in| Persistency
number. | length. | | 1/100000. | curve.
--------+---------+-----------+--------------+------------
63 | 7082 | 0 | |
62 | 6957 | 1 | |
60 | 6728 | 7 | |
58 | 6520 | 18 | |
57 | 6423 | 28 | |
56 | 6330 | 43 | |
54 | 6152 | 76 | 900 | 2
52 | 5996 | 90 | 250 | 7
50 | 5850 | 95 | 130 | 13·5
48 | 5720 | 93 | 60 | 29
46 | 5596 | 83 | 34 | 51
44 | 5481 | 71 | 22 | 80
42 | 5321 | 58 | 18·5 | 92
40 | 5270 | 46 | 17·5 | 100
38 | 5172 | 32 | 18 | 94
36 | 5085 | 21 | 19·5 | 90
34 | 5002 | 12·5 | 22 | 79
32 | 4924 | 7 | 27 | 65
30 | 4848 | 4·5 | 34 | 51
28 | 4776 | 3·0 | 40 | 38·5
25 | 4675 | 1·5 | 60 | 29
20 | 4518 | 0·4 | 250 | 7
19 | 4488 | 0·0 | 350 | 5
16 | 4404 | -- | 600 |
--------+---------+-----------+--------------+------------
INDEX
PAGE
Absorption by the Yellow Spot 90
Artificial Spectrum 33
Cases of Defective Colour Vision unrecognised 67
Clerk Maxwell’s Colour-Box 42
Clerk Maxwell’s Colour Curves 47
Colour, and the Sensations required to produce it 50
Colour Blindness due to Disease 137
Colour-Blind Persons see a Grey in the Spectrum 65
Colour Discs 32
Colour Fields 13
Colour Matches made by the Colour Blind 70
Colour Patch Apparatus 18
Colour Patch Apparatus, Original Form of 19
Comparison of the Young and Hering Theory 189
Complex Colours matched by Simple Colours 22
Contrast Colours 187
Curious Case of Congenital Colour Blindness, A 164
Dalton Colour Blindness 58
Daltonism, or Colour Blindness 57
Defective Form Vision connected with Colour Deficiency due to
Disease 138
Definition at different parts of the Retina 11
Enfeebled Spectrum Luminosity 98
Exhibiting Colour Blindness by Colour Discs 74
Extinction and Persistency Curves of Green-Blind Persons 127
Extinction and Persistency Curves of Monochromatic Vision 125
Extinction and Persistency Curves of Red-Blind Persons 127
Extinction of Colour 105
Extinction of Light by the Centre and Periphery of the Eye 114
Extinction of Colour of equal Luminosity 110
Extinction of Light in the Spectrum 109
Eye: Explanation of its Functions 3
Fatigue of the Retina 6, 30
Field of View 10
Fovea Centralis 4
Fundamental Light 34
Green-Blind Person’s Description of the Spectrum, A 64
Green Monochromatic Vision 131
Helmholtz Diagram of Sensations 38
Heredity in Colour Blindness 58
Hering’s Colour Vision Theory 52
Hering’s Theory not tri-chromic 57
Holmgren’s Colour Tests 169
Kœnig’s Colour Sensation Curves 49
Lissajou’s Figures 37
Luminosity of the Spectrum to the Centre of the Eye, the Fovea
Centralis, and outside the Yellow Spot 88
Luminosity of the Spectrum to partially Colour Blind 86
Luminosity of the Spectrum to the Colour Blind 81
Luminosity of the Spectrum to the Normal Eyed 78
Malingerers, Detection of 185
Matching Colours by Mixtures of Simple Colours 26
Maxwell’s Colour Equations 202
Maxwell’s Curves for Red Blindness 69
Measurement of Colour Fields 207
Monochromatic Vision and the Spectrum 66
Number of Cones in the Eye 8
Optograms 9
Pellet Tests 146
Pendulum Experiments 36
Persistency Curves 119
Primary Colours 25
Primary Pigment Colours 27
Progressive Atrophy of the Optic Nerve 153
Purkinje’s Figures 7
Purples 24
Red and Green matched 72
Red-Blind Person’s Description of the Spectrum, A 63
Retina, Structure of 6
Retinal Fatigue 6, 30
Rods and Cones 8
Seat of Visual Sensation 7
Sensation Curves in Terms of Luminosity 93
Sensitiveness of the Eye 121
Simple Colours 17
Simulation of Red and Green Blindness 175
Spectrum described by the Tobacco Blind, The 143
Spectrum Test for Colour Blindness 181
Table of Wave-Lengths 17
Tables 211
Tobacco Ambyopia 140
Tobacco Blindness, Examples of 148
Violet Blindness 73
Visibility of an Object in light of different Colours 123
Visual Purple 9
White Monochromatic Vision 158
Wool Test, The 170
Yellow Spot 4
Yellow Spot and Colour Mixtures, The 28
Young’s Theory, Modification of 196
WORKS ON PHOTOGRAPHY
BY
CAPT. W. DE W. ABNEY, C.B., D.C.L., F.R.S., _Late Royal Engineers_.
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Transcriber’s Notes
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.
Simple typographical errors were corrected; unbalanced quotation
marks were remedied when the change was obvious, and otherwise left
unbalanced.
Illustrations in this eBook have been positioned between paragraphs.
The index was not checked for proper alphabetization or correct page
references.