Eratosthenes measured the angle of the shadow cast by a vertical pillar in Alexandria when the Sun was directly overhead in the Egyptian city of Syene, to the south of Alexandria, at noon on the summer solstice, He used this angle and the distance to calculate the Earth's circumference, and thence radius.
His calculation was given in stadia (the circumference was something over 39,000 stadia; the radius was something over 6,000 stadia). A Greek stadion (according to Herodotus) consisted of 600 podes. But the length of the pos, and hence the stadion, varied in the Greek world. (For a brief discussion of some ancient measurements, see Herodotus Bk II: [
penelope.uchicago.edu]).
Metric measurements were not introduced until 3,000 years later (as mentioned here - [
www.maatforum.com]).
John Taylor: [
en.wikipedia.org].
A Dissertation upon the Sacred Cubit of the Jews and the Cubits of the several Nations: Isaac Newton (John Greaves, Miscellaneous Works of Mr. John Greaves, Professor of Astronomy in the University of Oxford, vol. 2 (London: 1737), pp. 405-433.) - [
www.newtonproject.ox.ac.uk]
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