Title: Comparison of Earth size measuring methods in the ancient Greek world
Author(s): A.D. Pinotsis (Oral)

ABSTRACT
  In previous work of ours, (Pinotsis 1993, 2000) we studied thoroughly the contribution of Poseidonius of Rhodes to astronomy, philosophy, mathematics, geography, cartography and mechanics. We discussed and explained there  the astronomical method used by Poseidonius to estimate the length of earth’s meridian.
  In the present paper we look through ancient Greek sources and examine the methods which were developed in order to measure the size of the earth. We conclude that two were the most important : The geometrical method by Eratosthenes and the astronomical one by Poseidonius of Rhodes. Both give remarkable results very close to earth’s actual size. We compare these two methods and present the errors that each one makes. Both seem to have been developed by perceptive men with multifarious talents.