He first went to Bechuanaland as a missionary in 1841; on his extensive travels in the interior he discovered Lake Ngami (1849), the Zambezi River (1851), and the Victoria Falls (1855). In 1866 he led an expedition into central Africa in search of the source of the Nile; after many hardships he was eventually found in poor health by the explorer Sir Henry Morton Stanley on the eastern shore of Lake Tanganyika in 1871.