David Brion Davis, professor of history at Yale University and one of the world's leading authorities on slavery, delivered the Nathan I. Huggins Lectures last week (April 30, May 1-2). The three lectures were titled: 'The Origins and Nature of New World Slavery,' '1819: Signs of a New Era,' and 'The African-American Impact on American Abolitionism and Southern Responses to the Perils of Antislavery.' The lectures were sponsored by the W.E.B. Du Bois Institute.