Transcriber’s Notes:
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in the original text.
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in the original text.
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Illustrations have been moved so they do not break up paragraphs.
Deprecated spellings have been preserved.
Typographical and punctuation errors have been silently corrected.
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[Illustration: PLATE IX.]
THE LAWS OF CONTRAST OF COLOUR:
AND THEIR APPLICATION TO THE ARTS
OF
PAINTING, DECORATION OF BUILDINGS, MOSAIC WORK, TAPESTRY AND
CARPET WEAVING, CALICO-PRINTING, DRESS, PAPER-STAINING,
PRINTING, MILITARY CLOTHING,
Illumination, Landscape, and Flower Gardening, &c.
BY M. E. CHEVREUL,
DIRECTOR OF THE DYE WORKS OF THE GOBELINS,
ETC. ETC.
TRANSLATED FROM THE FRENCH BY
JOHN SPANTON.
_NEW EDITION_,
With Illustrations printed in Colours.
LONDON:
ROUTLEDGE, WARNE, AND ROUTLEDGE,
FARRINGDON STREET.
NEW YORK: 56, WALKER STREET.
1861.
CONTENTS.
PAGE
INTRODUCTION 1
PART THE FIRST.
SECTION I.—ON THE LAW OF SIMULTANEOUS CONTRAST OF COLOURS,
AND OF ITS DEMONSTRATION BY MEANS OF EXPERIMENT 4
CHAP. I.—Manner of observing the Phenomena
of the Simultaneous Contrast of Colours. Definition
of Simultaneous Contrast 4
CHAP. II.—The Law of the Simultaneous Contrast
of Colours, and the Formula which represents it 8
CHAP. III.—The Law of Simultaneous Contrast of Colours
demonstrated by the Juxtaposition of a certain Number
of Coloured Bodies 10
CHAP. IV.—On the Juxtaposition of Coloured
Surfaces with White 18
CHAP. V.—On the Juxtaposition of Coloured Bodies with Black 19
CHAP. VI.—On the Juxtaposition of Coloured Bodies with Grey 21
CHAP. VII.—On the Juxtaposition of Coloured Bodies belonging
to the Colours of the same Group of Coloured Rays 24
CHAP. VIII.—On the Application of the Law of Contrast to the
Hypothesis that Red, Yellow, and Blue are the only
Primary Colours; and that Orange, Green, Indigo, and Violet
are Secondary or Composite Colours 25
SECTION II.—ON THE DISTINCTION BETWEEN SIMULTANEOUS, SUCCESSIVE,
AND MIXED CONTRAST OF COLOURS, AND ON THE CONNEXION BETWEEN
THE EXPERIMENTS MADE BY THE AUTHOR, AND THOSE PREVIOUSLY
MADE BY OTHER OBSERVERS. DISTINCTION BETWEEN SIMULTANEOUS,
SUCCESSIVE, AND MIXED CONTRAST OF COLOURS 29
PART THE SECOND.
ON THE APPLICATION OF THE LAW OF SIMULTANEOUS CONTRAST
OF COLOURS 34
Introduction 34
Definition of the words Tones, Scales, and Hues 34
Of Diagrams designed to represent and define Colours
and their Modifications 36
Harmony of Colours 46
Assortments of Red, Orange, Yellow, Green, Blue,
and Violet with White, Black, and Grey 49
Colours with White 50
Colours with Black 54
Colours with Grey 58
FIRST DIVISION.—IMITATION OF COLOURED OBJECTS WITH COLOURED
MATERIALS IN A STATE OF INFINITE DIVISION 68
Introduction 68
Painting on the System of Chiaro-’scuro 69
Painting on the System of Flat Tints 81
SECTION III.—ON COLOURING IN PAINTING 82
CHAP. I.—On Colouring 82
Of Aërial Perspective 83
Of Colouring in respect to the Harmony of the Colours
of the various Objects composing the Picture 85
CHAP. II.—Utility of the Law of Simultaneous
Contrast of Colours in the Art of Colouring 87
Utility of this Law in order to imitate promptly and
surely the Modification of Light on the Model 89
Utility of the Law in order to Harmonize those Colours
of a Composition which are inherent to the Nature
of the Object represented 95
SECOND DIVISION.—IMITATION OF COLOURED OBJECTS BY MATERIALS
OF A DEFINITE SIZE, AS THREADS, &C. 102
CHAP. I.—On the Elements of Gobelins Tapestry 104
RULE I.—The Binary Mixture of Primary Colours 104
RULE II.—The Mixture of Complementary Colours 105
RULE III.—The Mixture of the Three Primary Colours in such
proportions that they do not become neutralized, because
one or the other of them is in excess 108
THIRD DIVISION.—COLOUR PRINTING 118
On Calico-Printing, and printing Paper-hangings 118
False Judgment of the Value of Recipes for Colouring
Compositions 119
CHAP. II.—On the Law of Simultaneous Contrast of
Colours in relation to Paper-hangings with Figures,
Landscapes, or large Flowers of varied Colours 121
On the Law of Simultaneous Contrast of Colours
relatively to the Borders of Paper-hangings 123
Printed or written Characters on Papers of different
Colours 136
On the Assortment of Colours for reading by diffused
Daylight 138
FOURTH DIVISION.—EMPLOYMENT OF COLOURS IN ARCHITECTURE 138
1. On the Employment of Colours in Egyptian Architecture 138
2. On the Employment of Colours in Greek Architecture 139
3. On the Employment of Colours in Gothic Architecture 141
Application to the Interior of Edifices 143
On the Assortment of Stuffs with the Wood of Seats 143
On the Selection of Frames for Pictures and Engravings 145
On the General Decoration of the Interiors of Churches 147
On the Decoration of Museums and Galleries 149
Decorations of the Interior of Houses 152
On the Assortment of Colours in Interiors, the Walls of
which are panelled or covered with Marble, Stucco,
or Painted Wood 163
FIFTH DIVISION.—CLOTHING 165
I. MEN’S CLOTHING 165
Of the Advantages of Contrast, considered with regard
to the apparent Cleanliness of Cloth for Clothing 165
II. FEMALE CLOTHING 167
Colours for the Dress of Women with White Skins 167
Of the Colours of the Hair and Head-dress 168
Of the Colours of the Complexion and the contiguous
Drapery 169
The Head-dress in relation to the Coloured Rays which it
may reflect upon the Skin 171
Fair-haired Type 175
Type with Black Hair 176
On the Assortment of Colours in the Dress of
Women with Copper-coloured Skins 177
On the Assortment of Colours in the Dress of
Women with Black or Olive Skins 177
APPLICATIONS TO HORTICULTURE.
On the Art of arranging ornamental Plants in Gardens, so
as to derive the greatest possible advantage from the
Colours of their Flowers 180
Assortments of Flowers where the Plants are apart 181
Assortments relating to the Harmonies of Contrast of Hues 182
Assortments as to Harmony of Analogy 182
On the Art of assorting Ligneous Plants in Gardens, so as
to derive the best possible advantage from the Colour
of their Foliage 184
On the Distribution and Planting of Trees, &c., in Masses 185
Chap. I. Of Lines of Plants 187
Of the Lines of Plants called Screens 188
Of Lines of Plants considered as Elements of Masses 188
Of Homogeneous Masses 189
Of Heterogeneous or Varied Masses 190
Isolated 190
Contrast of Colours 194
Repetition 194
Symmetry 196
General Harmony 196
SIXTH DIVISION.—INTERVENTION OF THE PRECEDING PRINCIPLES IN
THE JUDGMENT OF COLOURED OBJECTS, RELATIVELY TO THEIR
COLOURS, CONSIDERED INDIVIDUALLY, AND TO THE MANNER IN
WHICH THEY ARE ASSOCIATED 197
On the Connexion of the Law of Simultaneous Contrast
of Colours with the Judgment we form upon all
Coloured Bodies, under the relations of the respective
Beauty or Purity of their Colours, and of the Equality
of the Distance of their Tones if these bodies belong to
the same scale 205
On the Comparison of two Samples of the same Colour 206
Influence of a Surrounding Colour upon one Colour
when compared with another 206
On the Effect of Contrast upon the Browns and the
Lights of most of the Scales of Wood and Silk employed
in Tapestry and Carpets 208
Means afforded by Contrast for ascertaining whether
the Tones of a Scale of Colour are equidistant 209
Of the Binary Associations of Colours, critically
considered 210
Of the Complex Association of Colours, reviewed
critically 214
Of the Arts which address the Eye by employing
Coloured Materials of a certain size, considered
relativelyto the Physical Condition of these Materials,
and to the Peculiarity of the Art employing them 218
Tapestries, Carpets, Mosaics, and Coloured Glass
Windows, corresponding to Paintings in Chiaro-’scuro 219
Of the Disposition of the Mind of the Spectator in
respect to the Judgment he forms of an Object of Art
which attracts his eye 225
ON THE COLOURS OF MILITARY UNIFORMS 227
INDEX 235
LIST OF ILLUSTRATIONS.
ENGRAVED AND PRINTED IN COLOURS BY EDMUND EVANS.
In referring to the illustrations, it will be necessary to cover
with white paper all but the example immediately under notice.
NOTE.—In Plates 8, 9, and 10, the examples are in rows
of 13 circles arranged lengthwise.
PLATE PAGE
1. DIAGRAMS, VARIOUS 4
2. EXPERIMENTAL DEMONSTRATIONS OF CONTRAST
OF COLOUR 7
3.} MODIFICATIONS WHICH THE PRINCIPAL COLOURS
4.} INDUCE IN CONTIGUOUS COLOURS 17
5.}
6. SIMPLE AND COMPOUND COLOURS 26
7. CHROMATIC DIAGRAM 36
8. ASSORTMENTS OF COLOURED CIRCLES:—
COLOURS WITH WHITE 51
9. DO. DO. BLACK 54
10. DO. DO. GREY 58
11. ELEMENTS OF GOBELINS TAPESTRY:—
THE BINARY MIXTURE OF PRIMARY COLOURS 104
12. DO. THE MIXTURE OF COMPLEMENTARY COLOURS 105
13. BLACK ORNAMENTS ON VARIOUS COLOURED GROUNDS 120
14. GREY DO. DO. DO. 123
15. METALLIC GILT ORNAMENTS ON DO. 124
16. BORDER OF BLUE FLOWERS ON DO. 130
17. BORDER OF ROSES AND LEAVES ON DO. 131
PREFACE TO THE THIRD EDITION.
The present edition has been entirely revised; some obscurities cleared
up, and a chapter on Military Clothing added. The application of
Chevreul’s reasoning will doubtless tend to a rational view of this
much debated question. It affords much satisfaction to all concerned
in the diffusion of the principles enunciated in this work, to observe
that they are being generally applied in this country, thus realizing
the hopes originally expressed by the translator.
TRANSLATOR’S PREFACE.
Colour, a universal source of enjoyment, so essential an element
of decorative art, has not been hitherto the subject of such
investigations as to place its powers, harmonies, and discordances
among matters of scientific certainty. A few traditionary dogmas have
been the only guide of ordinary workmen, while success in design, as
well as in the higher regions of art, has been dependent upon that rare
union of faculties vaguely denoted by the indefinite, unsatisfactory
term, “taste.”
The arrangement of colours in manufactures of English design—since the
decline of mediæval art—has commonly been condemned as notoriously
arbitrary, destitute of any reference to principle, and deficient
in that satisfying richness and beauty which result from harmonious
combinations. Although often overcharged with colour, and of costly
elaboration, our manufactures have too often proved that the
designer—in ignorance of a true, infallible standard—has mistaken
gaudiness for splendour, and capricious strangeness for improvement;
and, for want of a better claim to popular favour, has constantly
sought it by “leaning on novelty, his fickle, frail support.”
The established preference of French designs was shown, by the Great
Exhibition of 1851, to be, in the main, well-founded; and one of the
leading causes of the perfect success of some objects was found in
the fact, that they had been designed and executed in accordance with
a well-defined set of principles, extensively taught in France to
designers, workmen, and others. These principles it is the purpose of
this book to set forth, to illustrate, and to apply to every art of
which the choice and arrangement of colours is an element.
The author, M. Chevreul, before the publication of this work, had
gained high reputation by his researches in organic chemistry. In his
“Considerations sur l’Analyse Organique,” he enunciated principles
which, carried into practice in his “Recherches sur les Corps Gras
d’origine animal,” opened the path which has been rendered illustrious
by Liebig and others. But, being appointed Director of the Dye Works of
the Gobelins, he was compelled to abandon these researches—the field in
which, “having sown, he had, as it were, only to reap,”—that he might
fully investigate the principles involved in the assortment of colours.
M. Chevreul’s earnest attention to this inquiry was continued during
ten years, with ample opportunities for investigation. For twenty-five
years he has been in the habit of lecturing to workmen, artists, &c.
The undisputed superiority of those French manufactures in which these
instructions have been fully carried out, has evinced his success and
rewarded his exertions.
Aware of the important influence of such knowledge, the Chamber of
Commerce of Lyons solicited and obtained from the French Government
permission for M. Chevreul to lecture there to the artisans especially,
to whom printed copies of the lectures were afterwards gratuitously
distributed.
As the present Work contains the substance of these instructions, we
may hope that our own industrious countrymen may not long be without a
similar advantage.
The value of this book has been universally recognised, and it
has already been translated into several languages, although but
recently into our own. A recent critic has said, with equal truth and
eloquence,—“Rarely has a subject of inquiry, so fraught with beautiful
and ready applications, been presented to us. To be familiar with this
book is to possess a new sense. Every object in art and nature speaks a
new and exciting language. Colour becomes music to the eye. We become
impatient of any violent infringement of the principles of harmony,
and seek every opportunity of putting our newly-acquired knowledge
into practice. The minuteness of investigation, and the copiousness of
illustration which characterize this volume are truly remarkable; the
most untutored mind cannot fail to understand it, if steady attention
be given. As a preparation for a course of scientific study, it is
invaluable, for it is an excellent example of the Baconian method of
investigation.”
EXTRACTS FROM THE AUTHOR’S PREFACE.
In seeking to discover the causes of the complaint made of the quality
of certain colours prepared in the dyeing laboratory of the Gobelins,
I was at once convinced, that, although the complaints concerning
the instability of the light blues, greys, and browns, might be well
founded, there were others, especially those of a want of vigour in
the blacks employed for the shadows of blue and violet draperies,
which were not so; for, having procured black-dyed wools from the most
celebrated dye works in France and other countries, and having found
that they were not superior to those of the Gobelins, I saw that the
want of vigour alleged against the blacks was owing to the colours
contiguous to them, and that the matter was involved in the phenomena
of _the contrast of colours_.
It was thus demonstrated to me that I had two absolutely distinct
subjects to investigate, in order to fulfil my duties as Director of
the Dye Works; the first being the contrast of colours, considered
in the most general manner, both in relation to science and to its
applications: the second—the chemistry of dyeing. These are the two
centres around which have converged all my researches during the last
ten years.
In fact, numerous observations made during several months, on the view
of coloured objects, which were verified by my pupils and others, much
accustomed in their profession to judge of colours and to appreciate
the least differences between them, have been collected and described
as well-known facts. Upon reflecting on the mutual relations of these
facts, and in seeking the principle of which they were the results,
I was led to the discovery of that which I have named the “Law of
Simultaneous Contrast of Colours.” Thus this work is the fruit of the
method _à posteriori_: facts are observed, defined, described, then
generalized in a simple expression, which has all the characters of
a law of nature. This law, once demonstrated, becomes a means, _à
priori_, of assorting coloured objects so as to obtain their best
possible effect, according to the taste of the person who arranges
them; it becomes also a means of estimating whether the eyes are well
organized for seeing and judging of colours; and whether painters have
copied exactly the colours of known objects.
In reviewing the Law of Contrast with regard to its application,
and in submitting to experiment all the laws which appear to me to
result from it, I have been led to extend it to the arts of tapestry,
to the various sorts of painting and printing, to illuminating,
horticulture, &c. But, in order to anticipate the judgments of some
readers, upon the value of the opinions I have advanced (2nd part,
2nd division) respecting the Gobelins and Beauvais tapestry and the
Savonnerie carpets, I must state, that, being an entire stranger to
the inspection and direction of the works which are executed in the
Royal manufactories, as well as to the choice of models, my views and
opinions should be regarded only as those of an individual who has had
frequent occasion to see and examine various artistic productions, on
the preparation of which he could exercise no influence, the duties
which attach me to the Gobelins being exclusively those of Director of
its Dye Works.
THE LAWS OF
Harmony and Contrast of Colours.
INTRODUCTION.
1. A ray of solar light is composed of an indeterminate number of
variously coloured rays, which are distributed into groups, termed _red
rays, orange rays, yellow rays, green rays, blue rays, indigo rays,
violet rays_.
2. But all the rays comprised in the same group, the red for example,
are not identical in colour; on the contrary, they may be considered
as differing more or less among themselves, although we recognise the
impression they produce separately, as comprised in that which we
ascribe to red light.
3. When light is reflected by an opaque white body, it is not modified
in proportion to the variously coloured rays which constitute white
light; but, 1. _If the body is not polished_, every point of its
surface is to be considered as dispersing the white light which falls
upon it, in all directions, into the surrounding space; so that the
point becomes visible to an eye placed in the direction of one of its
rays. We may easily conceive that the image of the body, in a given
position, is composed of the sum of the physical points, which send to
the eye so placed, a portion of the light which each point radiates. 2.
_If the body is polished_, as, for example, the surface of a mirror,
a portion of the light is irregularly reflected, as in the preceding
case; while another portion is regularly reflected, giving to the
mirror the property of presenting to an eye, suitably placed, the image
of the body which sends its light to the reflector. One consequence
of this distinction is, that if we regard two plane surfaces which
reflect white light, and differ from each other only in polish, it will
happen that where the unpolished surface is visible, all its parts
will be equally, or almost equally, illuminated; while the eye, when
in a position to receive only the light which it reflects irregularly,
will receive very little light from the polished surface; but it will
receive much more light when in a position to receive that which is
regularly reflected.
4. If the light which falls on a body is completely absorbed by that
body, so that it disappears from sight, as in falling into a perfectly
dark cavity, then the body appears to us black; and it becomes visible
only because it is contiguous to surfaces which reflect or transmit
light. We know of no bodies which are perfectly black, and it is only
because they reflect a little white light that we judge they have
relief, like other material objects.
5. When light is reflected by an opaque coloured body, there is always
a reflection of white light, and a reflection of coloured light; the
latter is owing to the fact that the body absorbs or extinguishes
within itself some of the coloured rays, and reflects the others.
It is evident that the _absorbed_ coloured rays are of a different
colour from the _reflected_ coloured rays; and farther, that if these
be reunited with the former, white light will be reproduced. It is
evident, also, that unpolished opaque bodies reflect irregularly white
light, and the coloured light which makes them appear coloured; and
that those which are polished reflect irregularly a portion only of
these two lights, while they reflect regularly the other portion.
6. It thus appears, by what has been said concerning the physical
composition of solar light, that if the whole of the coloured light
which is absorbed by a coloured body were reunited with the whole of
the light which it reflects, white light would result. Now, it is
this property of two variously coloured lights, taken in a certain
proportion, to reproduce white light, that we express by the words
_coloured lights complementary to each other_, or _complementary
colours_. It is in this sense that we say,
Red is complementary to Green, and _vice versâ_.
Orange ” ” Blue, ” ”
Greenish-Yellow ” Violet, ” ”
Indigo ” ” Orange-Yellow, ”
7. It must not be supposed that a red body, a yellow body, &c.
reflects, besides white light, only the red rays or yellow rays, &c.,
each of these bodies reflects also every sort of coloured rays; but,
the rays which cause us to judge it to be red or yellow, &c., being
more numerous than the others, produce more effect than they; yet, the
latter have an undoubted influence in modifying the action of red and
yellow rays upon the organ of sight. This explains the innumerable
diversities of colour observable among various red bodies, various
yellow bodies, &c. It is difficult not to admit that among these
diversely coloured rays reflected by bodies, there are a certain number
which, complementary to each other, must reproduce white light upon
reaching the retina.
PART THE FIRST.
SECTION THE FIRST.
OF THE LAW OF SIMULTANEOUS CONTRAST OF COLOURS, AND
OF ITS DEMONSTRATION BY MEANS OF EXPERIMENT.
CHAPTER I.
_Manner of observing the Phenomena of the Simultaneous
Contrast of Colours._—_Definition of Simultaneous
Contrast._
8. If we look at the same time at two stripes of unequal tints of the
same colour, or at two stripes of equal tints of different colours,
in juxtaposition, that is to say, contiguous by one of their edges,
the eye will perceive, if the stripes be not too wide, certain
modifications; in the first case affecting the intensity of the two
tints, in the second, the optical composition of the two colours
so placed. Now as these modifications cause the colours to appear,
when looked at together, more different than they really are, I have
given to them the name of the _simultaneous contrast of colours_. The
modification which affects the intensity of colour, I term _contrast of
tone_; and the modification which affects the optical composition of
the contiguous colours, I term _contrast of colour_.
The twofold phenomena of contrast of colour and contrast of tone may be
readily shown by the following.
_Experimental Demonstration of Contrast of Tone._
Plate A Aʹ.
9. Let the two halves of a sheet of unglazed paper, about twenty inches
square, be coloured clear grey, by a mixture of chalk and black; fix
them, in any way, upon a piece of unbleached linen, placed across a
window, at the distance of twelve inches asunder. Take two halves of
another piece of similar paper B Bʹ, but of a darker grey, and coloured
with the same substances. Fix A next to B and place Bʹ twelve inches
from B. (See Fig. 1.)
[Illustration: PLATE I.]
Upon looking at the four half-sheets for a few seconds, it will be
seen that A contiguous to B will be lighter than Aʹ, while B will seem
darker than Bʹ.
10. It is easy to demonstrate that the modification is not equally
intense over the whole of the surfaces A Aʹ and B Bʹ, but that it
becomes gradually feebler from the line of contact. This may be proved
by placing a card, so cut, that O and P may each present three grey
stripes, as shown in Fig. 2, Plate 1. The stripes 1 1 are more modified
than the stripes 2 2, and these are more so than the stripes 3 3.
However, in order that this modification may be effected, it is not
absolutely necessary that O and P should touch; for if the stripes 1 1
be covered, the stripes 2 2, 3 3 will be modified.
11. The following experiment, which is simply the result of the two
preceding (9 and 10), is well suited to demonstrate the extent of
contrast of tone. Upon a sheet of cardboard divided into ten stripes,
each about a quarter of an inch broad, lay a uniform tint of Indian
ink. As soon as it is dry, lay a second tint on all the stripes except
the first. As soon as the second is dry, lay a third on all the stripes
except the first and second, and so on of all the rest, so as to
have ten flat tints, gradually increasing in depth from the first to
the last. (See Fig. 3.) If ten strips of paper of the same grey, but
each of a different tone, be laid upon a cardboard, in the preceding
gradation, it will serve the same purpose.
Upon looking at the cardboard, it will be seen that the strips, instead
of presenting flat tints, will each appear of a tone diminishing in
intensity from the edge _a a_ to the edge _b b_. In the stripe 1, the
contrast is produced simply by the contiguity of the edge _b b_ with
the edge _a a_ of the stripe 2; in the stripe 10, it is simply by the
contiguity of the edge _a a_ with the edge _b b_ of the stripe 9.
But in each of the intermediate stripes 2, 3, 4, 5, 6, 7, 8, 9, the
contrast is produced by a double cause; partly by the contiguity of the
edge _a a_ with the edge _b b_ of the stripe which precedes it, partly
by the contiguity of the edge _b b_ with the edge _a a_ of the darker
tint which follows it. The first cause tends to raise the tone of the
half of the intermediate stripe; while the second cause tends to lower
the tone of the other half of the same stripe.
In consequence of this contrast, the stripes seen from a proper
distance, resemble channels rather than flat surfaces. For, in the
stripes 2 and 3 for instance, the grey is weakened from the edge _a
a_ to the edge _b b_, presenting to the eye the same effect as if the
light fell upon a channelled surface; there is however this difference,
that in the real channelling the enlightened part would throw a
reflection upon the dark portion.
12. Contrast of tone occurs with colours so called as well as with
grey; thus to repeat the experiment (9), fig. 1, with the halves _o o_
of a sheet of paper of a light tint of a certain colour, and the two
halves _p p_ of a sheet of paper of a darker tint of the same colour,
it will be seen that _o_ contiguous to _p_ will be lighter than _oʹ_,
and _p_ darker than _pʹ_. In short, it may be demonstrated as has been
done (10) that the modification of colours in juxtaposition becomes
weaker in proportion to their distance from the line of contact; and in
order to observe this effect in bodies which are not contiguous, it is
only necessary to experiment as described in (10).
[Illustration: PLATE II.]
The colours experimented upon must be as nearly as possible of equal
intensity.
13. _Experimental Demonstration of Contrast of Colour._—If we arrange
as before, the two halves of an unglazed coloured sheet of paper, and
two halves of another sheet of a different colour, but as nearly as
possible of equal intensity, or rather of _tone_ (8), upon looking
at the four half-sheets _o oʹ, p pʹ_ for a few seconds, we shall see
that _o_ differs from _oʹ_ and _p_ from _pʹ_; consequently the two
half-sheets, _o p_, seem to undergo a reciprocal modification of tint,
which is rendered apparent by comparing their colours with those of
_oʹ_ and _pʹ_.
14. No 1. { Red inclines to Violet.
{ Orange ” Yellow.
2. { Red ” Violet.
{ Yellow ” Green.
3. { Red ” Yellow.
{ Blue ” Green.
4. { Red ” Yellow.
{ Indigo ” Blue.
5. { Red ” Yellow.
{ Violet ” Indigo.
6. { Orange ” Red.
{ Yellow ” Bright Green.
7. { Orange ” Bright Red.
{ Green ” Blue.
8. { Orange ” Yellow.
{ Indigo ” Blue.
9. { Orange ” Yellow.
{ Violet ” Indigo.
10. {Yellow ” Bright Orange.
{ Green ” Blue.
11. { Yellow ” Orange.
{ Blue ” Indigo.
12. { Green ” Yellow.
{ Blue ” Indigo.
13. { Green ” Yellow.
{ Indigo ” Violet.
14. { Green ” Yellow.
{ Violet ” Red.
15. { Blue ” Green.
{ Indigo ” Deep Violet.
16. { Blue ” Green.
{ Violet ” Red.
17. { Indigo ” Blue.
{ Violet ” Red.
15. It thus appears from the experiments described in this chapter that
two coloured surfaces in juxtaposition, viewed simultaneously, present
to the eye two modifications—one relative to the depth of tone of their
respective colours, and the other relative to the physical composition
of those colours.