European exploration of Africa and Lake Victoria. It was eventually proved to be the latter from which the Nile flowed. Henry Morton Stanley, who had in 1871 succeeded in finding and succouring Livingstone (originating the famous line "Dr. Livingstone, I presume"), started again for Zanzibar in 1874. In one of the most memorable of all exploring expeditions in Africa, Stanley circumnavigated Victoria Nyanza (Lake Victoria) and Lake Tanganyika. Striking farther inland to the Lualaba, he followed that river down to the Atlantic Ocean—which he reached in August 1877—and proved it to be the Congo. In 1895, the British South Africa Company hired the American
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