These tree-presences of Corot are painted very flatly. The roundness of their bulk disappears into a flat mass. It was one of the ways in which he avoided the suggestion of solidity. But here again comes in the fact that a principle may have other applications; for flatness does not necessarily make the object appear unsubstantial. A house does not look so, yet its front may be flat. And Corot, as other artists, and as you may, if you use your eyes, had discovered that in the open air all objects appear flatter than they do indoors. The reason is that in the case of a room lighted by windows, the light is always stronger near the windows than it is in parts of the room further removed. The light is unequally distributed, so that there are more shadows to throw up the bulk of objects. But out of doors the light is more diffused; more equally distributed. Moreover, we view things from a greater distance, so that more atmosphere intervenes. The effect of both these facts is to make the masses of objects seem flatter. The lawn from a little distance may look very smooth; but, when you walk over it, you find the grass needs to be cut and the bumps to be rolled before you can play croquet. That maple, too, is a sturdy, solid fellow, but as you see its mass of pale green against the darker mass of hemlock, both seem flatter than they do when you are climbing among their branches.