Buddy diving just before and after the Second World War. After the invention of the "aqualung" by Cousteau and Gagnan, the first commercially underwater breathing apparatus became available for sale for sporting purposes in the late 1940s. As the new sport of scuba diving rapidly expanded through the 1950s, several sporting organisations—notably the YMCA—began programmes to train swimming enthusiasts in this new aquatic pastime, and began to codify what they believed were proper practises for this expanding sport. The YMCA considered the buddy system a useful corollary to the "never swim alone" rule of their swimming and lifesaving programmes. Cousteau himself independently
New materials in 20th-century art Delaunay and scores of young artists in Paris made their first modern paintings venturing toward abstraction and other new ways of formulating figurative, still-life and landscape imagery. During the first decade of the 20th century modern art developed simultaneously in several different areas in Europe (France, England, Scandinavia, Russia, Germany, Italy), and in the United States. Artists began to formulate different directions of modern art, seemingly unrelated to one another. In printmaking, the linocut was invented by the artists of Die Brücke in Germany between 1905 and 1913. At first they described their prints as woodcuts, which sounded more respectable.