Thanks for the relay of these messages. My colleague Dieter Forster (Physics) says it was known that Syene was the northernmost point at which one would witness the equatorial direct-sun-overhead effect: on the 23rd degree of latitude, at the tropic of Cancer. So it was, he believes, perhaps well-known for this feature.
Then Eratosthenes' light bulb really was a light bulb, connecting two known phenomena the relationship of which had never been noticed. This makes more sense to me than the thought of him strolling down Aswan Blvd. and suddenly realizing that the sun was straight up, hiring an agent in Alexandria, etc. The distances between the places aren't a major obstacle, I should think. I wonder if ERatosthenes' "error" results from a mismeasure of these distances? Dan Tompkins
