How Eratosthenes calculated the circumference of the Earth

January 30, 2012 | By | Reply More

One of Dan Sperber’s favorite explanations belongs to Eratsthenes (276-195 BCE) who used a few local observations to calculate the circumference of the Earth to within 1% of the modern measurement. Sperber carefully walks us through Eratsthenes’ calculations, then comments:

Was Eratosthenes thinking concretely about the circumference of the earth (in the way he might have been thinking concretely about the distance from the Library to the Palace in Alexandria)? I believe not. He was thinking rather about a challenge posed by the quite different estimates of the circumference of the Earth that had been offered by other scholars at the time. He was thinking about various mathematical principles and tools

Image by NASA

that could be brought to bear on the issue. He was thinking of the evidential use that could be made of sundry observations and reports. He was aiming at finding a clear and compelling solution, a convincing argument. In other terms, he was thinking about representations—theories, conjectures, reports—, and looking for a novel and insightful way to put them together. In doing so, he was inspired by others, and aiming at others. His intellectual feat only makes sense as a particularly remarkable link in a social-cultural chain of mental and public events. To me, it is a stunning illustration not just of human individual intelligence but also and above all of the powers of socially and culturally extended minds.

Sperber’s article is one of one of 192 this year in response to’s annual question: “What is Your Favorite Deep, Elegant, or Beautiful Explanation.”


Category: Science

About the Author ()

Erich Vieth is an attorney focusing on consumer law litigation and appellate practice. He is also a working musician and a writer, having founded Dangerous Intersection in 2006. Erich lives in the Shaw Neighborhood of St. Louis, Missouri, where he lives half-time with his two extraordinary daughters.

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