Earth science
Eratosthenes of Cyrene [b. Cyrene (Shahhat, Libya), c. 276 bce, d. Alexandria, c. 194 bce] calculates Earth's circumference, finding a value 15 percent higher than present estimates or even closer, depending on what one assumes about the actual length of the Greek measure called a stadium. See also 450 bce Astronomy.
Eratosthenes gives the first correct explanation for the annual flood of the Nile, relating it to rains over lakes in East Africa that are the Nile's source.
MathematicsEratosthenes invents the sieve of Eratosthenes, a method that discovers all prime numbers (whole numbers with no whole-number factors other than one and themselves) up to a given prime factor. He also develops a mechanical device that can be used to double the cube. See also 420 bce Mathematics.
| Millennium: | 1st millennium BC |
| Centuries: | 4th century BC – 3rd century BC – 2nd century BC |
| Decades: | 270s BC 260s BC 250s BC – 240s BC – 230s BC 220s BC 210s BC |
| Years: | 249 BC 248 BC 247 BC 246 BC 245 BC 244 BC 243 BC 242 BC 241 BC 240 BC |
| Categories: | Births – Deaths – Architecture Establishments – Disestablishments |
Contents: 249 BC 248 BC 247 BC 246 BC 245 BC 244 BC 243 BC 242 BC 241 BC 240 BC
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