The atmosphere around the Earth contains vast quantities of essential substances (water, dust, etc.) besides oxygen, which influence the dissemination of light. That is why we see things that are at a distance not only as more vague and obscure, but due to the selective absorption of light, as bluer. This phenomenon is called atmospheric perspective. It was known long before Turner (Giotto, Leonardo), but was never used so consciously to express spatial relations. The characteristic of Turner’s pictorial space is that he emphasized the atmosphere, the negative space between the objects. (Norham Castle, Sunset)