Someone knows who measured the Earth Radius and the methods that used?
The last of those websites given by robphy:
is probably the one you want since it talks about Eratosthenes and how he determined the radius of the earth.
By the way: notice that he did that about 2000 years before Columbus! The myth has it that Columbus believed the earth was round while everyone else thought it was flat. That is nonsense, of course, any educated person of the time, and certainly any ship captain or navigator, knew perfectly well that the earth was round. The truth is that Columbus believed the earth was much smaller than Erastosthenes calculation. And, of course, he was WRONG!
The reason Columbus (and many others) believed the earth was much smaller than that is interesting: they simply believed that it didn't make sense that all of the land area was on one side of the earth and only ocean on the other! Apparently it never occured to them that there were other lands on the other side of the earth.
Halls, there was another reason scholars in the Middle Ages thought the Earth was smaller than Eratosthenes said; their source was Ptolemy, and he had the circumference of the Earth equivalent to 16,000 miles instead of 24,000. This wasn't the only case in which Ptolemy gave a bogus number that confused later generations. He was a good calculator but a somewhat feckless and less than honest observer.
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