

June 19, 240 B.C.: The Earth Is Round, and It's This Big - nreece
http://www.wired.com/science/discoveries/news/2008/06/dayintech_0619

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demallien
I'm always left stunned when I read about the achievements of Eratosthenes.
I've always wondered why he doesn't get the same recognition as Plato or
Aristotle, or even Socrates.

~~~
0x44

      I've always wondered why he doesn't get the same recognition as Plato or Aristotle, or even Socrates.
    

Very likely because most of his works were destroyed when the Library at
Alexandria was razed, and because he wasn't considered the best at any single
subject by his contemporaries.

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lisper
There's a flaw in Eratostenes reasoning: you have to assume that the sun is
effectively infinitely far away. In Eratosthenes's day there was no way to
know this. The one measurement he did does not prove the world is round. It
could merely indicate that the sun is nearby. (It makes an interesting
exercise to calculate just how near it would have to be, and to design another
experiment to eliminate this possibility.)

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gambling8nt
Actually, Aristarchus, a contemporary of Eratosthenes (slightly earlier in
fact) determined the ratio distance to the sun/distance to the moon to be
about 20 (actual answer is about 390), and that the distance to the moon was
about 20 Earth radii (although Archimedes credited him with an approximation
closer to 80 Earth radii; the actual value is about 60). This would have
validated any assumption about the sun being far enough away to generate
essentially parallel rays.

Incidentally, the fact that the world was round was probably already known by
Eratosthenes' time, since the Greek society was essentially a group of
seafarers, and when you watch a ship go out to sea, in addition to appearing
smaller as it gets further away, it also appears to sink downwards. They would
doubtless have noticed this, and concluded that the Earth was probably round.

~~~
cconstantine
I've heard the last bit about the boats too. There is a theory that the common
folk never really thought that the earth was flat, but a round earth jived
with other theories at various times in history (turtles all the way down!)
causing the literate few to reject what simple observation makes clear.

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jgrahamc
There's a clearer explanation of what he did here:
[http://www.algonet.se/~sirius/eaae/aol/market/collabor/erath...](http://www.algonet.se/~sirius/eaae/aol/market/collabor/erathost/)
and this is a nice experiment to do yourself.

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edw519
_One reason is that Eratosthenes' very own library of Alexandria had been
destroyed, and there was no complete backup of its data._

Imagine how much different the world would be today if the Egyptians had
practiced disaster recovery.

(Also a good lesson for a few customers of mine.)

~~~
t0pj
_library of Alexandria had been destroyed_

I think we're still _recovering_ from that infamous day.

~~~
jsmcgd
I feel sick when I think of all that was lost.

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arundelo
There's a kids' picture book about Eratosthenes called The Librarian who
Measured the Earth:

<http://www.amazon.com/gp/product/0316515264>

