Starting from Khartoum in January 1869, he went up the White Nile to Bahr-el-Ghazal, and then, with a party of ivory dealers, through the regions inhabited by the Diur (Dyoor), Dinka, Bongo and Niam-Niam; crossing the Congo-Nile watershed he entered the country of the Mangbetu (Monbuttu) and discovered the river Uele (March 19, 1870), which by its westward flow he knew was independent of the Nile.