This effect of atmosphere is one of the things that we are now going to discuss. The other is that atmosphere penetrates everywhere. Suppose we begin with the second point. The atmosphere is in one respect like water; it is a fluid. It flows in and out and around about and fills the whole space that is not occupied by some other body. But have you thought what this means to an artist? Or at least to some artists; for we said that Copley’s pictures contained little or no suggestion of atmosphere. And the same may be said of a great many pictures by modern artists. They represent the form and color of things, but do not suggest that they are surrounded, or, as is often said, enveloped in atmosphere.