This play of light and shade, which also photography has rendered common-place, had interested Elstir so much that at one time he had painted what were almost mirages, in which a castle crowned with a tower appeared as a perfect circle of castle prolonged by a tower at its summit, and at its foot by an inverted tower, whether because the exceptional purity of the atmosphere on a fine day gave the shadow reflected in the water the hardness and brightness of the stone, or because the morning mists rendered the stone as vaporous as the shadow.