History of Africa Other significant European explorers included Heinrich Barth, Henry Morton Stanley (coiner of the term "Dark Continent" for Africa in an 1878 book), Silva Porto, Alexandre de Serpa Pinto, Rene Caille, Friedrich Gerhard Rohlfs, Gustav Nachtigal, George Schweinfurth, and Joseph Thomson. The most famous of the explorers was David Livingstone, who explored southern Africa and traversed the continent from the Atlantic at Luanda to the Indian Ocean at Quelimane. European explorers made use of African guides and servants, and established long-distance trading routes were used. Missionaries attempting to spread Christianity also increased European knowledge of Africa. Between 1884 and 1885, European
19th century in science later in the 19th century by the German mathematician Bernhard Riemann; here no parallel can be found and the angles in a triangle add up to more than 180°. Riemann also developed Riemannian geometry, which unifies and vastly generalizes the three types of geometry. The 19th century saw the beginning of a great deal of abstract algebra. Hermann Grassmann in Germany gave a first version of vector spaces, William Rowan Hamilton in Ireland developed noncommutative algebra. The British mathematician George Boole devised an algebra that soon evolved into what is now called Boolean algebra, in which the only numbers were