Antiquity. Eratosfen

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It is necessary to mention two more geniuses ellinisticheskogo the world: Eratosfena (276-194 BC) and Gipparha (apprx. 190-125 BC).

Eratosfen was born in Cyrene (North Africa), studied in Alexandria and Athenes. It was the tutor of crown prince Ptolemeja of III Everita, and from 225 BC managed the Alexandria library. Among its scientific interests were: astronomy, geography, mathematics, physics, ethnography and many other things. In 240 BC it has measured an arch of a meridian and has calculated a circle of the Earth for what has spent measurements of height of the Sun in Siena, in the south of Egypt, and to Alexandrias which lie approximately on one meridian, at the moment of a summer solstice. Knowing distance between these cities, it has defined length of a circle of the Earth 250 thousand stages (1 stage== 185 that is very close to the modern data.

So witty Eratosfen has estimated distance to the Moon and an inclination ekliptiki: for this purpose it used that fact that the difference between Sun heights in a summer and winter solstice is equal about 11/83 lengths of a circle. Proceeding from this difference, it has calculated an inclination during 23 hailstones. 51 minutes, very close to the modern.

Eratosfen has offered chronological system, in which dates were counted from time of falling of Troy, and each 4 years superfluous day was entered into a calendar, and has made a map of Ojkumeny - a manned part of the Earth, more exact, than all preceding.

Its mathematical works were so brilliant: a method of definition of simple numbers (' resheto Eratosfena '), the device for the decision of a problem on doubling of a cube and others.