Around the World

          I recently bought a new used car with about a hundred-thousand miles on it.  In the life of a Subaru that's really not all that many miles if you follow the maintenance guidelines.  For most people mileage on a car is really just a number, an indicator of when to get an oil change or a timing belt replacement.  I myself never thought of it as more than a number until the used car salesman mentioned “ya cars been around the earth about four times”.  I just thought, “Wow!  I'm buying a car that has done that?  The circumference of the earth is 24,902 miles.  Most miles are just driving around town with occasional weekend trips or even possibly a road trip across the country.  I'm sure if you mapped peoples driving habits it really wouldn't be all that interesting.  Just a bunch of really dense lines with random single lines jetting out into open space.  However, the salesman’s comment really made me think a little more about the circumference and spatial details of our planet.

          The circumference of the Earth after Aristotle argued the Earth was round was figured out by Eratothenes circa 200 B.C. He figured the circumference to within a half percent of accuracy.  This really astonishes me.  Not only the accuracy but the simple fact that it was done far before any one had traveled the circumference or without any modern technology to assist him.  To determine this he took measurements of shadow heights in two different parts of Egypt at specific times and then calculated the angle between the two.  From this he was able figure out how big a circle was needed to complete 360 degrees.  Eratosthenes thought that precise mapping really depended on accurate linear measurements.  I really don't think he could have been more correct in this thought.  The amount of perception and mathematical skill Eratosthenes had was truly amazing.  He was also the first person to use the word geography.  In my mind, Eratosthenes made one of the most significant if not the single most important contributions to modern cartography as we know it.