The Analysis

Abstract This chapter examines how Eratosthenes could have used a sundial to determine the angle of a shadow cast in Alexandria equivalent to 1/50 of the circumference of a circle (which is an integral part of his calculation of the circumference of the Earth). This was done by comparing the ratio of the distance between the base of the gnomon and the intersection of the noon and Summer Solstice lines on the face of the sundial for two instruments calibrated for two different locations (Alexandria and Syene). The concludes with a number of sections which individually examine the potential errors that are inherent in the assumed knowledge that Eratosthenes was working from, and other forms of error within the experiment, to determine their impact on the resultant calculations.

This examination demonstrates that all of the potential sources of error had such a minimal impact of Eratosthenes’ result as to be negligible.