Day 4 is for science and today's subject is Eratosthenes (276-194 BC). The chief librarian of Alexandria who devised a way to measure the earth's size. I've read this page two times and my mind is still boggled. It took a water well, the sun and a measuring stick. Oh, and a pacer - a professional walker trained in taking perfectly equal steps. What?!? On June 21st, the longest day of the year, Eratosthenes got crackin' with his plan to visit a special well in the neighboring town of Syene and wait for the sun to hit the bottom of the well. That time was 12 noon. By seeing the bottom of the well this meant that the sun was directly overhead in Syene, which was due north of his town of Alexandria. If the sun was directly overhead in Syene then the suns rays must be hitting at an angle in Alexandria. On June 21st (I'm assuming the following year, they don't say) Eratosthenes took a measuring stick and captured the angle cast by the shadow. He knew the