The clouds in many 19th-century European paintings look drastically different than those in the 18th century. There are layers…

hyperallergic:

The clouds in many 19th-century European paintings look drastically different than those in the 18th century. There are layers to their texture, with whisps of cirrus clouds flying over billowing cumulus, and stratus hovering low. Clouds weren’t classified by type until 1802, and their subsequent study influenced artists from John Constable to J. M. W. Turner.

How the Naming of Clouds Changed the Skies of Art