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IMAGES TO ACCOMPANY: January 19, 2008: The Librarian Who Could

Eratosthenes of Cyene(276 BC - 194 BC): The Librarian who first measured the world.

 

Eratosthenes calculated Earth's circumference by measuring the distance along a 1/50th arc of the great circle. (Between Alexandria and Syene) He assumed that Earth was perfectly spherical and by using a simple ratio derived his value for the distance around Earth.

The distance between Alexandria and Syene was known to be about 5000 Stadia. We assume that the stadion measurement he employed was the Egyptian stadion. One Egyptian stadion equals about 157.5 meters. With this measurement, Eratosthenes' circumference value is about 24,608 miles. (This value is surprisingly accurate, as it is within 1% of the modern accepted value of 24,901.55 miles (equatorially) and 24,859.82 miles (between the poles)