Festival of Maps exhibit (Chicago)





f you should happen to be in Chicago between now and January 31, 2008, be sure to visit the more than 30 cultural and scientific institutions (including Encyclopaedia Britannica) participating in the citywide Festival of Maps exhibit, highlighting how the technology of wayfinding has evolved from ancient times to the present.

In about 240 BC, a Greco-Egyptian poet and librarian named Eratosthenes conducted an unusual experiment. He had heard that at noon on the summer solstice, and on that day only, the sun shone straight down into a deep well at what is now Aswan, along the Nile River. Drawing on his knowledge of geometry, Eratosthenes conjectured that the well lay along one of the earth’s tropics, and he hypothesized that he could measure the circumference of the earth by triangulating from that well to Alexandria, a distance of about 5,000 stadia, or about 500 miles, and calculating the difference in degrees.

Traveling to the site of the distant well, as New York Times science writer John Noble Wilford recounts in the opening pages of his lively book The Mapmakers, Eratoshenes made his measurements and ran out the numbers. He arrived at an estimate of the equivalent of 46,000 kilometers—a mark that, while still far from the earth’s true circumference of about 40,000 kilometers, was much more accurate than earlier maps (almost all of which, incidentally, recognized that the earth was roundish) had managed to attain....


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