L'optique des couleurs. Fondée sur les simples observations, & tournée sur-tout à la pratique de la peinture, de la teinture & des autres arts coloristes.

1740. Paris, Briasson, 1740. 12mo. Halftitle, title, xviij, 487, (v), (ii) pp. The last two pages contain a catalogue of books newly published by Briasson. Contemporary full calf binding, spine goldtooled. (top & bottom of spine & corners slightly rubbed). Edges stained red. Only edition and a nice clean copy of this important work which unfortunately lacks the two plates although seems they have never been bound into this particular copy. The colour circle or wheel is a common form adopted for colour systems. They have been used since the Middle Ages. Castel created a color wheel based on colour as a combination of light and shadow. He began with determining the colours in the rainbow. Newton's seven principal colors were not enough; Castel found at least a thousand; impossible to differentiate among them such a large number of colors in a circle of any practical size. Moreover, Castel suggested, his use of the color circle was merely a convenient substitute for the color spiral, that could incorporate increasing paleness or darkness along a series of colors. In L'Optique des couleurs Castel explained the twelve colors he chose to include in his circle. Castel's choice of twelve colors, and his choice of colors to include, was closely related to the twelve tones of the musical scale. Clarification of the relationship between color and sound, occupied Castel for many years, especially his plans for and construction of an occular harpsichord, an instrument to play color as a harpsichord plays sound. Castel was convinced that a specifically French science existed as did a specifically French music and a specifically French art. Castel declared that Newton's hypotheses were inadequate, as they gave primacy to mathematical descriptions: Castel believed that his system was better because it began with observation and rational thought.