European exploration of Africa 1840s, so that around the midpoint of the 19th century and the beginning of the colonial Scramble for Africa, the unexplored parts were now limited to what would turn out to be the Congo Basin and the African Great Lakes. This "Heart of Africa" remained one of the last remaining "blank spots" on world maps of the later 19th century (alongside the Arctic, Antarctic and the interior of the Amazon basin). It was left for 19th-century European explorers, including those searching for the famed sources of the Nile, notably John Hanning Speke, Sir Richard Burton, David Livingstone and Henry Morton
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