Cite web page as: Monticello: observation tower, recto, circa 1771, by Thomas Jefferson. N66; K39 [electronic edition].
Thomas Jefferson Papers: An Electronic Archive. Boston, Mass. : Massachusetts Historical Society, 2003. http://www.thomasjeffersonpapers.org/
Original manuscript: Jefferson, Thomas. Monticello: observation tower, 1 sheet, 2 pages, circa 1771. N66; K39. Dimensions: 36.5 cm x 23 cm (14-3/8" x 9-1/16"). Original manuscript from the Coolidge Collection of Thomas Jefferson Manuscripts, Massachusetts Historical Society. Rendering of an observation tower, with specifications and notes on verso; never built.