Whether there be any thing in colours, which corresponds to the harmony between sounds, may be doubted. If there be, it must, however, admit of much greater latitude than the harmony between sounds, since all mixtures and degrees of colours, unless where the quantity of light overpowers the eye, are pleasant; however one colour may be more so originally than another. Black appears to be originally disagreeable to the eyes of children; it becomes disagreeable also very early from associated influences. In adults, the pleasures of mere colours are very languid in comparison of their present aggregates of pleasure, formed by association. And thus the eye approaches more and more, as we advance in spirituality and perfection, to an inlet for mental pleasure, and an organ suited to the exigencies of a being, whose happiness consists in the improvement of his understanding and affections. However, the original pleasures of mere colours remain, in a small degree, to the last, and those transferred upon them by association with other pleasures (for the influence is in these things reciprocal, without limits) in a considerable one. So that our intellectual pleasures are not only at first generated, but afterwards supported and recruited, in part, from the pleasures affecting the eye; which holds particularly in respect of the pleasures afforded by the beauties of nature, and by the imitations of them, which the arts of poetry and painting furnish us with. And for the same reasons the disagreeable impressions on the eye have some small share in generating and feeding intellectual pains.
It deserves notice here, that green, which is the colour that abounds far more than any other, is the middle one among the primary colours, and the most universally and permanently agreeable to the eye of any other; also, that as the common juice of vegetables is in general green, so that of animals is in general red; the first being, perhaps, of the third order, the last of the second. It appears to be extremely worth the time and pains of philosophers to inquire into the orders of the colours of natural bodies, in the manner proposed and begun by Sir Isaac Newton; and particularly to compare the changes of colour, which turn up in chemical operations, with the other changes which happen to the subjects of the operations at the same time. Nothing seems more likely than this to be a key to the philosophy of the small parts of natural bodies, and of their mutual influences.
Here we may make the following observations: First, that the ideas of this sense are far more vivid and definite than those of any other; agreeably to which, the word idea denoted these alone in its original and most peculiar sense.
