A cloud atlas is a pictorial key (or an atlas) to the nomenclature of clouds. Early cloud atlases were an important element in the training of meteorologists and in weather forecasting, and the author of a 1923 atlas stated that "increasing use of the air as a means of transportation will require and lead to a detailed knowledge of all the secrets of cloud building."
Throughout the 19th century nomenclatures and classifications of cloud types were developed, followed late in the century by cloud atlases. The first nomenclature ("naming", also "numbering") of clouds in English, by Luke Howard, was published in 1802. It followed a similar effort in French by Jean-Baptiste Lamarck in 1801. Howard's nomenclature defined four fundamental types of clouds: cirrus or thread-cloud, cumulus or heap-cloud, stratus or flat cloud (level sheet), and nimbus or rain-cloud (see Classification of clouds). There followed a long period of development of the field of meteorology and the classification of clouds, leading up to 1896, the International Year of Clouds. The history of this period is the subject of a popular book, The Invention of Clouds. During that time, the Englishmen Rev. Clement Ley and Hon. Ralph Abercromby, were influential. Both men died before the classification was settled, however. Ley wrote a book, Cloudland, that is well known to meteorologists. Abercromby contributed a number of papers on the subject, stressing the most important (and then novel) fact that clouds are the same everywhere in the world. He also wrote in collaboration with Hugo Hildebrand Hildebrandsson a detailed classification of clouds. This was adopted in Hildebrandsson's 1890 Cloud Atlas.