Solo diving II. In the late 1940s, after the invention of the Aqua-lung by Cousteau and Gagnan, the first retail underwater breathing apparatus for sport was commercially marketed. As the sport expanded through the 1950s, several sporting organisations – notably the Young Men's Christian Association (YMCA) – began scuba training programmes for swimming enthusiasts, thus began the codification of what was believed to be proper practices for the expanding amateur sport of scuba diving. The buddy system was thought to be a useful corollary to the "never swim alone" edicts of the YMCA swimming and lifesaving programmes. Cousteau independently implemented a buddy
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.