The first person who attempted to supply the organ of vision with the luxuries of light and colour, was Father Castel, a learned Jesuit, who had distinguished himself chiefly by his opposition to the splendid optical discoveries of Newton. About the year 1725 or 1726, he published in the Mercure de Paris, his first ideas of an organ, or ocular harpsichord. A full account of this curious instrument was afterwards published at Hamburgh, in 1739, by M. Tellemann, a German musician, who had seen one of the harpsichords in the possession of the inventor, when he was on a visit to Paris. This account was afterwards translated into French, and printed at the end of Castel’s L’Optique des Couleurs,[18] which appeared at Paris in 1740. The ocular harpsichord is a common harpsichord, fitted up in such a manner, that when a certain sound is produced by striking the keys, a colour related to that sound is at the same instant exhibited to the eye in a box or frame connected with the harpsichord; so that when a piece of music is played for the gratification of the ear, the eye is simultaneously delighted by the display of corresponding colours.
In adjusting the colours and the sounds, Castel lays down the following six propositions:—
1st,—There is a fundamental and primitive sound in nature, which may be called ut, and there is also an original and primitive colour, which is the foundation of all other colours, namely, blue.
2d,—There are three chords, or essential sounds, which depend upon the primitive sound ut, and which compose with it a primitive and original accord, and these are ut, mi, sol. There are also three original colours depending on the blue, which, while they are not composed of any other colours, produce them all, namely, blue, yellow, and red. The blue is here the note of the tone, the red is the fifth, and the yellow is the third.
3d,—There are five tonic chords, ut, re, mi, sol, la, and two semitonic chords, fa and si. There are also five tonic colours, to which all the rest are ordinarily related, namely, blue, green, yellow, red, and violet, and two semitonic or equivocal colours, namely, aurora and violant (related to the orange and indigo of Newton).
4th,—Out of these five entire tones, and two semitones, is formed the diatonic scale, ut, re, mi, fa, sol, la, and si; and, in like manner, out of the five entire or tonic colours, and the two demi-colours, are formed the gradation of colours, blue, green, yellow, aurora, red, violet, and violant; for the blue leads to green, which is demi-blue; the yellow to aurora, which is gilded yellow; the aurora leads to red, the red to violet, which is two-thirds of red, and one-third of blue; and the violet to violant, which has more blue than red.
5th,— The entire tones divide themselves into semitones; and the five entire tones of the scale or gamut, comprehending in this the two natural semitones, make twelve semitones, viz., ut natural, ut dieze, re, re dieze, mi, fa, fa dieze, sol, sol dieze, la, la dieze, and si. In like manner there are twelve demi-colours, or demi-tints, and there can be neither more nor less, according to the opinion of painters themselves, and as may be demonstrated by other means. These colours are blue, sea-green, green, olive, yellow, aurora, orange, red, crimson, violet, agathe, and violant. Blue leads to sea-green, which is a greenish blue; sea-green leads to green; green to olive, which is a yellowish green; olive to yellow; yellow to aurora; aurora to orange; orange to red, the colour of fire; red to crimson, which is red mixed with a little blue; crimson to violet, which is still more blue; violet to agathe, or bluish violet; and agathe to violant.
6th,—The progression of sounds is in a circle, setting out from ut, and returning back: thus, ut, mi, sol, ut, or ut, re, mi, fa, sol, la, si, ut. This is called an octave, when the last ut is one-half more acute than the first. The colours also have their progression in a circle.
7th,—After an octave, ut, re, mi, fa, sol, la, si, there recommences a new one, which is one-half more acute, and the whole circle of music produces several octaves.
Such are the principles upon which the ocular harpsichord was founded; but though the instrument, from its singularity, excited great attention when it was first constructed, we have not been able to learn that it was ever supposed to possess the power of affording pleasure to the eye. It must be obvious, indeed, to any person who considers the subject, that colour, independent of form, is incapable of yielding a continued pleasure. Masses of rich and harmonious tints, following one another in succession, or combined according to certain laws, would no doubt give satisfaction to a person who had not been familiar with the contemplation of colours; but this satisfaction would not be permanent, and he would cease to admire them as soon as they ceased to be new. Colour is a mere accident of light, which communicates richness and variety to objects that are otherwise beautiful; but perfection of form is a source of beauty, independent of all colours; and it is therefore only from a combination of these two sources of beauty that a sensation of pleasure can be excited.