Eratostene (276 BC - 194 BC)

Scientist, inventor

Eratosthenes was a Greek scientist that studied mathematics, geography, astronomy and was even a poet. He is mainly remembered for having measured the length of the Earth circumference. He computed this length as 252.000 stadia. If the Egyptian stadium is assumed (that is about 157.5 meters) the measure made by Eratosthenes is 3969000 meters, hence the error is lower than 1 %. Around 255 b.C. Erathostenes is credited with having invented the armillar sphere, a device very similar to a spherical astrolabius. In 245 b.C. was invited in Egypt to teach to the future Pharaos (Ptolemy IV Philopator). Around 240 b.C., Ptolemy III Euergetes appointed Eratosthenes director of the Great Library of Alexandria. Ptoleny affirms that Eratosthenes computed the tilt of the Earth's axis as 11/83 of 180°, that is to say 23° 51’ 15".
Eratosthenes is also known for having invented a mesolabius, a device to compute the cubic root (problem of Delos or problem f the cube duplication) that is very important for many technical applications expecially in Mechanics. He also proposed a simple algorithm for the determination of the prime numbers and draw a map of Earth surface.

variant spelling:
Eratostene

Curriculum vitae

* 275 BC - 277 BC	Cyrene	born
254 BC - 256 BC		Invented the armillar sphere
239 BC - 241 BC		Measured the length of the Earth circumference
235 BC - 237 BC		Was appointed director of the Library of Alexandria
219 BC - 221 BC		Invented a mesolabius
194 BC - 196 BC		Became blind
† 193 BC - 195 BC	Alexandria of Egypt	died

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Permanent links

DMG-Lib		https://www.dmg-lib.org/dmglib/handler?biogr=8222004
Europeana		http://www.europeana.eu/portal/record/2020801/dmglib_handler_biogr_8222004.html

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Eratostene (276 BC - 194 BC)