When necessity has borne the artist out of this zone, the peaceful domain of the imitator, he finds himself impelled to produce effects which are no longer the simple phases of color, but such as the means at his disposal fail to accomplish. In the simpler stages of coloring, when he desired to represent an object as blue or red, it was but necessary to use blue or red material. Now he has advanced to a point where this principle is no longer applicable. The illuminative power of light compels new methods of manipulation. As examples of a thorough comprehension of the need of such a change in the employment of means, of the character of that change, of the skill necessary to embody its principles, and of utter success in the result, we have but to suggest the name and works of Titian. But the laws which Titian discovered have been unheeded for centuries; and they might have remained so, had not the mind of William Page felt the necessity of their revival and use. To him there could be no chance-work. Art must have laws as definite and immutable as those of science; indeed, the body in which the spirit of art is developed, and through which it acts, must be science itself. He saw, that, if exact imitation of Nature be taken as the law in painting, there must inevitably occur the difficulty to which we have before referred,--that, above a certain point, paint no longer undergoes transfiguration, thereby losing its character as mere coloring material,--that, if the ordinary tone of Nature be held as the legitimate key-note, the scope of the palette would be exhausted before success could be achieved. Any one of Turner's latest pictures may serve to illustrate the nature of this difficulty. Although in his early practice he was remarkable for his judicious restraint, it is evident that the splendors of the higher phenomena of light had for him unlimited fascination; and he may be traced advancing cautiously through that period of his career which was marked by the influence of Claude, toward what he hoped would prove, and perhaps believed to be, a realization of such splendors. It must have been observed by those who have studied his later pictures, that, while the low passages of the composition are wonderfully fine and representative, all the higher parts, those supposed or intended to stand for the radiance of dazzling light, fail utterly in representative capacity. There is an abundance of the most brilliant pigment, but it is still paint,--unmitigated ochre and white lead. The spectator is obliged to recede from the picture until distance enables the eye to transmute the offending material and reconcile the conflicting passages.