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 angle of the shadow was equivalent to the angle formed by the two cities and the center of the earth. Are you with me?
There's division happening, and fraction making and percentages taking place. What a brain this man had! There's even a little quip about a nickname given to him by his contemporaries, "Beta". He had so many interests that they considered him a dabbler, which they attributed to being second-class, a beta. (I think they were just jealous.)
This brilliant man estimated the circumference of the earth to be 24,700 miles. Today, using the exact same principles developed by Eratosthenes 2,000 years ago, modern instruments estimate the distance around the equator to be 24,902 miles.
There's so much more to learn! I'm really enjoying this book. (I need to read this page again.)