25. Martin Isler, «The Gnomon in Egyptian Antiquity», in JARCE, 28, 1991, pp. 167–168, and «An Ancient Method of Finding and Extending Directions», in JARCE, 26, 1989, pp. 201–202. See also E. C. Krupp, op. cit, pp. 197–199. Also N. Lockyer, The Dawn of Astronomy, London, 1894, pp. 192–195.
