David Livingstone was a Scottish Congregationalist pioneer medical missionary with the London Missionary Society and an explorer in Africa, one of the most popular national heroes of the late-19th-century in Victorian Britain. His fame as an explorer and his obsession with discovering the sources of the River Nile was founded on the belief that if he could solve that age-old mystery, his fame would give him the influence to end the East African Arab-Swahili slave trade. His subsequent exploration of the central African watershed was the culmination of the classic period of European geographical discovery and colonial penetration.Livingstone was one of the first Westerners to make a transcontinental journey across Africa in 1854–56, from Luanda on the Atlantic to Quelimane on the Indian Ocean near the mouth of the Zambezi.Livingstone completely lost contact with the outside world for six years and was ill for most of the last four years of his life.Henry Morton Stanley had been sent to find him by the New York Herald newspaper in 1869. He found Livingstone in the town of Ujiji on the shores of Lake Tanganyika on 10 November 1871, greeting him with the now famous words "Dr. Livingstone, I presume?" Livingstone responded, "Yes", and then "I feel thankful that I am here to welcome you." These famous words may have been a fabrication. However, the phrase appears in a New York Herald editorial dated 10 August 1872, and the Encyclopædia Britannica and the Oxford Dictionary of National Biography both quote it without questioning its veracity. The words are famous because of their perceived humor, Livingstone being the only other white person for hundreds of miles.