juxtaposed with one or another colour, as occurred in the instance (483.) when I compared the pattern of a border for paper-hangings (presenting roses with their leaves) placed upon a black ground, with a similar pattern placed upon a white ground; on comparing the two together, I saw the light green on the black ground yellower than upon the white, while three other persons, who compared the light tones of green with its deeper tones on the same ground, judged the light tones to be bluer upon the black than upon the white ground.

B. We might know the regularity of the successive states in which the eye is found during the sight of coloured objects and the law of simultaneous contrast of colours, and yet if we were ignorant of the influence of various degrees of intensity of light in varying the colour of bodies and in rendering the modifications of contrast more or less evident, we should be led to believe in an indefinite variation in the aspect of colours, while this variation is perfectly defined by the following remarks:

(a) If the direct light of the sun or diffused daylight illuminates a monochromous body unequally, the part most vividly lighted is modified as it would be if it received orange, and the modification appears the stronger the greater the difference of light on the parts (280.): thus, the more intense the light the more it gilds the body it illumines; it is thus always easy to foresee the effects of it, when we know the result of the mixture of orange with various colours.

(6) In a very vivid light the phenomena of simultaneous contrast being less evident than in a weaker light (63., 571.), it follows, if we neglected to take account of the difference in the effects, we should greatly deceive ourselves in our appreciation of the phenomena of contrast of similar colours. It is useful to remark that simultaneous contrast which tends to make the differently coloured parts appear as distinct as possible, is carried to a maximum

precisely when, the light being feeble, the eye requires the greatest contrast of colour to perceive distinctly the various parts upon which it is fixed. C. We may perceive the modifications presented by bodies when lighted, and experience much difficulty in accounting for them, for want of knowing how to exactly represent the modifications which the coloured materials experience in their colour, according as they receive light or white, shade or black, or according as they are mixed together. It is partly to make these modifications clearly known that I have designed the chromatic hemisphere (159. and following); in describing it I have attached less importance to its material realisation than to the rational principle upon which it rests. looking at the lines of this diagram independently of all colouring, we understand how any colour is reduced by white, deepened by black, and broken by black and white; lastly, how by mixture with a pure colour, it produces hues. I shall add subsequently some new considerations, which belong to the gradations of colour we make with coloured materials (841.).

On

D. The object I have had in view would not have been attained, if the chromatic hemisphere had not given me the means of representing, by a simple nomenclature, the modifications a colour undergoes by the addition of white and black, modifications which produce the tones of its scale; those which it receives from black yielding broken scales; lastly, those which, resulting from the addition of a pure colour, produce scales which are hues of the first colour.

Finally, to the definitions which I have given of the

words tone, scale, hue, broken colours, I must add the distinction of the associations of colours in harmonies of analogy, and harmonies of contrast (180.).

I am convinced that all those who accept the small number of definitions I have given, will find much

advantage in using them to account for the effects of colours, and to communicate to others the impressions they have received from them; by their aid it will be easy to seize relations which might have escaped observation, or which, in the absence of precise language, could not have been clearly expressed by those who perceived them.

E. It would be ignoring the reality, if I should attribute the opinion combated exclusively to simple ignorance of the facts recapitulated (A. B. C. D.), or to believe that it suffices to dissipate it, in order to establish the contrary opinion I profess: I am under no illusion; if ignorance is passive, and resists only by its inertia, it is quite otherwise with ideas more or less erroneous or pretentious, which exist on the sight of colours and their harmonies; these ideas actively repulse all that is opposed to them. I am satisfied with pointing out the obstacle, without having the least pretension to overthrow it, except by enouncing what I believe to be the truth.

In conclusion, by means of the positive facts which I have just reviewed, the study of the sight of coloured bodies leads to a certainty which all may acquire who henceforth give themselves up to it; they will see how fruitful it is in applications, and independent of all hypothesis, and that it would be impossible to obtain this result if there did not commonly exist among men an average organisation of the eye, which permits them to perceive (other things being equal) the same modifications in illuminated bodies: the difference, I admit, in the perception of the phenomena by divers individuals who have perfect organs of sight, bears only on the intensity of the perception.

(834.) The series of principles upon which my book is founded being reviewed, I next consider these facts under the three following relations, each of which will be the subject of a section:

1. Under the relation of the certainty they give in
judging of the colour of any object whatever.
2. Under the relation of the certainty they give to the
judgment we bring to the productions of the
various arts which address the eye by coloured
materials.

3. Under the relation of the union they establish be-
tween the principles common to many arts which
address to the eye various languages in employing
different materials.

Finally, in the last section, I shall treat of the influence that the disposition of the mind of the spectator may have upon the judgment he brings to any work of art exhibited.

SECTION I

INTERFERENCE OF THE LAW OF SIMULTANEOUS CONTRAST OF COLOURS WITH THE JUDGMENT WE EXERCISE UPON ALL COLOURED BODIES, VIEWED UNDER THE RELATION OF THE RESPECTIVE BEAUTY OR PURITY OF THE COLOUR AND OF THE EQUALITY OF THE DISTANCE OF THEIR RESPECTIVE TONES, IF THESE BODIES BELONG TO THE SAME SCALE.

INTRODUCTION (835.).

CHAPTER I. ON THE COMPARISON OF TWO PATTERNS OF THE SAME COLOUR (836.).

CHAPTER II.

ON THE INFLUENCE OF A SURROUNDING COLOUR UPON ONE COLOUR WHEN COMPARED WITH ANOTHER (837., 838.). CHAPTER III.-ON THE EFFECT OF CONTRAST UPON THE BROWNS AND THE LIGHTS OF THE GREATER PART OF THE SCALES OF WOOL AND SILK EMPLOYED FOR TAPESTRIES AND CARPETS (839.-841.).

CHAPTER IV.-MEANS AFFORDED BY CONTRAST OF ASSURING US IF THE TONES OF A SCALE OF COLOUR ARE EQUIDISTANT (842.).