c.276 - c.193 BC
Eratosthenes of Cyrene studied in Alexandria and Athens.
In Alexandria he was director of the great library. This scholar of natural history did his most outstanding work in mathematics and geography.
Eratosthenes calculated the circumference of the earth correctly. This he did by observing the different angle's that the sun's rays fall in two cities 500 miles apart.
He correctly assumed the Sun's distance to be so great that the rays are practically parallel when they reach the earth.
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From the University of St. Andrews, Scotland. School of Mathematics