In 1874, the "New York Herald," in partnership with Britain's "Daily Telegraph," financed Stanley on another expedition to the African continent. One of his missions was to solve a last great mystery of Africa by tracing the course of the Congo River to the sea. The difficulty of this expedition is hard to overstate. Stanley used sectional boats to pass the great cataracts that separated the Congo into distinct tracts. The boats had to be taken apart and transported around the rapids before being rebuilt to travel on the next section of river. After 999 days, on 9 August 1877, Stanley reached the Portuguese outpost of Boma, around 100 km from the mouth of the Congo River. Starting with 356 people, he reached Boma with 114 survivors, and he was the only European left. He wrote about his trials in his book "Through the Dark Continent".