"Some colors are more agreeable than others, but these differ with different eyes, and with the nature of the color to which the eyes have been previously exposed. A bluish green relieves the eye when over-excited with red, and a mild red is agreeable after the protracted action of intense green; and in general, the complementary colors are most agreeable in succession. Again, it is well known, that no kind of light is painful, unless excessively vivid; we are pleased with a mild radiance in objects of every hue, from the whiteness of the moon to the crimson of the setting sun. But is there no other physical property by which these luminaries directly contribute to the gratification of taste? It is true that light, abstractedly from all objects is agreeable, and agreeable on the same principle that sweetness is to the taste, i. e., from the mere character of the nervous impression. But this is a pleasure merely passive, and in an active being it is, perhaps, on that account, one grade lower than the gratification afforded by the beauty of form, and is more allied to the gross pleasure of literal taste. Hence, we scarcely employ a figurative expression, in declaring that light is sweet. But the highest degree of physical gratification is not enjoyed by the eye, unless this agreeable excitant proceeds from an object of beautiful form. "Light is sweet," but "it is a pleasant thing for the eyes to behold the sun." What is the source of this additional pleasure which we receive, when light proceeds either by radiation or reflection from regular curvilinear objects?