Gradation is so inseparable a quality of all natural shade and color that the eye refuses in art to understand anything as either, which appears without it, while on the other hand nearly all the gradations of nature are so subtile and between degrees of tint so slightly separated, that no human hand can in any wise equal, or do anything more than suggest the idea of them. In proportion to the space over which gradation extends, and to its invisible subtilty, is its grandeur, and in proportion to its narrow limits and violent degrees, its vulgarity. In Correggio, it is morbid and vulgar in spite of its refinement of execution, because the eye is drawn to it, and it is made the most observable and characteristic part of the picture; whereas natural gradation is forever escaping observation to that degree that the greater part of artists in working from nature see it not, (except in certain of its marked developments,) but either lay down such continuous lines and colors, as are both disagreeable and impossible, or, receiving the necessity of gradation as a principle instead of a fact, use it in violently exaggerated measure, and so lose both the dignity of their own work, and by the constant dwelling of their eyes upon exaggerations, their sensibility to that of the natural forms. So that we find the majority of painters divided between the two evil extremes of insufficiency and affectation, and only a few of the greatest men capable of making gradation constant and yet extended over enormous spaces and within degrees of narrow difference, as in the body of a high light. Sec. 18. How necessary in Art.