The Lewis and Clark expedition of 1804 1806 across America from Pittsburg to the Pacific and back was the third recorded transcontinental journey. President Jefferson had negotiated the Louisiana Purchase of over two million square kilometres from the French in 1803, and the aim of the expedition was to investigate the territory involved. He commissioned a Corps of Discovery as a scientific and military expedition to survey the acquisition, appointing his aide Meriwether Lewis (1774 1809) to lead it. It was hoped to discover that the Missouri and other rivers could be used for...