LEWIS, Meriwether, explorer, born near Charlottesville, Virginia, 18 August, 1774; died near Nashville, Tennessee, 11 October; 1809. He was a great-nephew of Fielding Lewis, noticed above, and inherited a fortune frown his father, who died when the son was a child. Meriwether, who was of a bold and adventurous disposition, left school at eighteen years of age, and in 1794 volunteered in the troops that were called out to quell the whiskey insurrection in western Pennsylvania. He entered the regular service in 1795, became captain in 1800, and in 1801-'3 was private secretary to President Jefferson, who in the latter year recommended him to congress to command an exploring expedition across the continent to the Pacific. 

He set out in the summer of 1803, accompanied by his associate, Captain William Clark, and a company that was composed of nine young men from Kentucky, fourteen soldiers, two Canadian boatmen, an interpreter, a hunter, and a Negro servant of Captain Clark. They began to ascend Missouri river in the spring of 1804, passed a second winter among the Mandans in latitude 47º 21' N., and on 7 April, 1805, continued to ascend the Missouri until the middle of July, when they reached the great falls. Near the close of this month they attained the confluence of three nearly equal streams, to which they gave the names of Jefferson, Madison, and Gallatin. They ascended the Jefferson to its source, traveled through the mountains from August till 22 September, when they entered the plains of the western slope, in October embarked in canoes on the Kooskoosky, a branch of the Columbia, and on 15 November reached the mouth of that river, after traveling more than 4,000 miles from the confluence of Mississippi and Missouri rivers. 

They passed the following winter on the south bank of the Columbia in an entrenched camp, in March, 1806, began to ascend the Columbia on their homeward journey, and in May left their boats and made a difficult journey on horseback across the mountains to the Missouri, upon which they re-embarked in August, reaching St. Louis in September, after an absence of two years and four months. Congress made grants of land to the men of the expedition and to their chiefs, and Lewis was made governor of Missouri territory.

He found the country torn by dissensions, and, although his impartiality and firmness soon restored comparative order, he began to suffer from hypochondria, to which he had been subject from his youth. During one of his attacks of depression he was called to Washington, and at a lodging-place in Tennessee he put an end to his life. Lewis and Clark, a county of Montana, is named in honor of the explorers. President Jefferson said of him: "He was courage undaunted, possessing a firmness of purpose which nothing but impossibilities could divert from its direction, and was intimate with Indian character, customs, and principles." A narrative of the expedition of Lewis and Clark, from materials that were furnished by the explorers, was prepared by Nicholas Biddle and Paul Allen, with a memoir of Lewis by Thomas Jefferson (2 vols., Philadelphia, 1814; new ed., with additions by Alexander McVickar, New York, 1843).