Eratosthenes, son of Aglaos, was a Greek philosopher born in 276 B.C.. He was a geographer(!), and a Librarian, too. He worked at the Library of Alexandria, which at the time, contained many valuable manuscripts. But what he was most famous for, was being the first one to accurately(so what if he was off by a few miles?) calculate the circumference of the Earth. One day, he was just sitting on his porch, reading the newspaper, when he spotted an interesting article about a well in Syene. On some particular occasions, at midday, the Sun would shine right down it, so that a boy could go down it and find all sorts of stuff that had been dropped down it. This place where the well was, in Syene, was right on the Tropic of Cancer. He was also directly North of Syene, and the distance between his location and the well was 5,000 stadia(a measurement of distance at the time).So with this information, went out into his yard, and measured the angle that the Sun was shining in his yard at noon. The angle was about 1/50 of a circle. Knowing the Earth was a perfect sphere, he multiplied the distance between him and Syene by 50, finding the circumference of the Earth.
Here are some pictures of him.
