Applying Manet's method, his invention, his discovery, to the painting of out-of-doors, the _plein air_ school immediately began to produce landscapes of astonishing reality by confining their effort to those values which it is in the power of pigments to imitate. The possible scale of mere correspondence being of course from one to one hundred, they secured greater truth by painting between twenty and eighty, we may say. Hence the grayness of the most successful French landscapes of the present day--those of Bastien-Lepage's backgrounds, of Cazin's pictures. Sunlight being unpaintable, they confined themselves to the representation of what they could represent. In the interest of truth, of reality, they narrowed the gamut of their modulations, they attempted less, upheld by the certainty of accomplishing more. For a time French landscape was pitched in a minor key. Suddenly Claude Monet appeared. Impressionism, as it is now understood, and as Manet had not succeeded in popularizing it, won instant recognition. Monet's discovery was that light is the most important factor in the painting of out-of-doors. He pushed up the key of landscape painting to the highest power. He attacked the fascinating, but of course demonstrably insolvable, problem of painting sunlight, not illusorily, as Fortuny had done by relying on contrasts of light and dark correspondent in scale, but positively and realistically. He realized as nearly as possible the effect of sunlight--that is to say, he did as well and no better in this respect than Fortuny had done--but he created a much greater illusion of a sunlit landscape than anyone had ever done before him, by painting those parts of his picture not in sunlight with the exact truth that in painting objects in shadow the palette can compass.