Six Experts Discuss American Antiques: There Is No Slackening of Interest in the Craftsmanship of Colonial Times EARLY AMERICAN FURNITURE. By Charles Over Cornelius. Illustrated. 278 pp. New York: The Century Company. $4. COLONIAL FURNITURE IN AMERICA. By Luke Vincent Lockwood Illustrated. 2 vols., 751 pp. New York: Charles Scriber's Sons. $30. MAHOGANY, ANTIQUE AND MODERN. Edited by William Farquhar Payson. Contributors: Charles Over Cornelius, Herry B. Culver, Ralph Erskine, Frances Morris, Kenneth M. Murchison, Meyric R. Rogers, Karl Schmieg. Illustrated 154 pp. New York: E.P. Dutton & Co. $15. MEASURED DRAWINGS OF EARLY AMERICAN FURNITURE. By Burl N. Osburn and Beotrico B. Osburn. Illustrated. 82 pp. Milwaukee :The Bruce Publishing Company. $1.80. THE COLLECTING OF ANTIQUES. By Esther Singleton. Illustrated. 338 pp. New York: The Macmillan Company. $7.50. AMERICAN GLAS. By Mary Harrod Northend. Illustrated. 209 pp. New York: Dodd, Mead & Co. $5.