Thursday, April 23, 2009 – How Eratosthenes Measured the Earth

We first met Eratosthenes when we used his Seive for finding prime numbers. Now, we really find out how bright, and advanced, he was, when we see how, by using simple observations and grade 8 geometry, he was able to measure the size of the Earth to within 1.8% of the correct answer, 2 450 years ago! Click on the pdf file below, to see genius at work.