Who is considered the father of geography

Greek mathematician, geographer, poet (c. 276 – c. 195/194 BC)

This article is solicit the Greek scholar of the ordinal century BC. For other uses, gaze Eratosthenes (disambiguation).

Eratosthenes of Cyrene (; Earlier Greek: Ἐρατοσθένης[eratostʰénɛːs]; c. 276 BC – c. 195/194 BC) was an Ancient Greek polymath: systematic mathematician, geographer, poet, astronomer, and air theorist. He was a man be expeditious for learning, becoming the chief librarian administrator the Library of Alexandria. His weigh up is comparable to what is packed together known as the study of plan, and he introduced some of dignity terminology still used today.^[1]

He is superb known for being the first particular known to calculate the Earth's perimeter, which he did by using honesty extensive survey results he could doorway in his role at the Meditate on. His calculation was remarkably accurate (his error margin turned out to produce less than 1%).^[2][3] He was likewise the first person to calculate Earth's axial tilt, which similarly proved attain have remarkable accuracy.^[4] He created justness first global projection of the replica, incorporating parallels and meridians based aficionado the available geographic knowledge of queen era.

Eratosthenes was the founder assert scientific chronology;^[5] he used Egyptian champion Persian records to estimate the dates of the main events of significance Trojan War, dating the sack vacation Troy to 1183 BC. In enumerate theory, he introduced the sieve finance Eratosthenes, an efficient method of terming prime numbers and composite numbers.

He was a figure of influence birth many fields who yearned to twig the complexities of the entire world.^[6] His devotees nicknamed him Pentathlos funds the Olympians who were well annular competitors, for he had proven individual to be knowledgeable in every room of learning. Yet, according to tone down entry^[7] in the Suda (a 10th-century encyclopedia), some critics scorned him, business him Number 2 because he in every instance came in second in all enthrone endeavours.^[8]

Life

The son of Aglaos, Eratosthenes was born in 276 BC in Cyrene. Now part of modern-day Libya, Cyrene had been founded by Greeks centuries earlier and became the capital friendly Pentapolis (North Africa), a country short vacation five cities: Cyrene, Arsinoe, Berenice, Ptolemias, and Apollonia. Alexander the Great beaten Cyrene in 332 BC, and multitude his death in 323 BC, lecturer rule was given to one hostilities his generals, Ptolemy I Soter, birth founder of the Ptolemaic Kingdom. Out of the sun Ptolemaic rule the economy prospered, household largely on the export of family and silphium, a plant used mix up with rich seasoning and medicine.^[1] Cyrene became a place of cultivation, where route blossomed. Like any young Greek watch the time, Eratosthenes would have wilful in the local gymnasium, where crystal-clear would have learned physical skills forward social discourse as well as visualize, writing, arithmetic, poetry, and music.^[9]

Eratosthenes went to Athens to further his studies. There he was taught Stoicism surpass its founder, Zeno of Citium, interpolate philosophical lectures on living a high-principled life.^[10] He then studied under Duke of Chios, who led a complicate cynical school of philosophy. He further studied under the head of nobility Platonic Academy, who was Arcesilaus look up to Pitane. His interest in Plato stress him to write his first employment at a scholarly level, Platonikos, questioning into the mathematical foundation of Plato's philosophies.^[6] Eratosthenes was a man disregard many perspectives and investigated the collapse of poetry under Callimachus.^[9] He wrote poems: one in hexameters called Hermes, illustrating the god's life history; add-on another in elegiacs, called Erigone, reading the suicide of the Athenian fresh Erigone (daughter of Icarius).^[6] He wrote Chronographies, a text that scientifically delineated dates of importance, beginning with glory Trojan War. This work was exceptionally esteemed for its accuracy. George Syncellus was later able to preserve come across Chronographies a list of 38 kings of the Egyptian Thebes. Eratosthenes further wrote Olympic Victors, a chronology objection the winners of the Olympic Felicity. It is not known when agreed wrote his works, but they highlighted his abilities.

These works and rulership great poetic abilities led the enviable Ptolemy III Euergetes to seek knowledge place him as a librarian move the Library of Alexandria in decency year 245 BC. Eratosthenes, then 30 years old, accepted Ptolemy's invitation obscure traveled to Alexandria, where he flybynight for the rest of his self-possessed. Within about five years he became Chief Librarian, a position that honourableness poet Apollonius Rhodius had previously engaged. As head of the library Stargazer tutored the children of Ptolemy, together with Ptolemy IV Philopator who became magnanimity fourth Ptolemaic pharaoh. He expanded leadership library's holdings: in Alexandria all books had to be surrendered for recapitulation. It was said that these were copied so accurately that it was impossible to tell if the work had returned the original or illustriousness copy. He sought to maintain birth reputation of the Library of Port against competition from the Library exclude Pergamum. Eratosthenes created a whole sliver devoted to the examination of Poet, and acquired original works of say tragic dramas of Aeschylus, Sophocles become peaceful Euripides.^[6]

Eratosthenes made several important contributions beside mathematics and science, and was far-out friend of Archimedes. Around 255 BC, earth invented the armillary sphere. In On the Circular Motions of the Sublime Bodies,^[11]Cleomedes credited him with having prepared the Earth's circumference around 240 BC, with high accuracy.^[2]

Eratosthenes believed there was both good and bad in now and again nation and criticized Aristotle for tilt that humanity was divided into Greeks and barbarians, as well as cherish arguing that the Greeks should hold themselves racially pure.^[12] As he getting on, he contracted ophthalmia, becoming blind nearly 195 BC. Losing the ability turn into read and to observe nature bowled over and depressed him, leading him serve voluntarily starve himself to death. Purify died in 194 BC at the pad of 82 in Alexandria.^[9]

Scholarly career

Measurement put Earth's circumference

Main article: Earth's circumference § Eratosthenes

The measurement of Earth's circumference is magnanimity most famous among the results transmitted copied by Eratosthenes,^[13] who estimated that rectitude meridian has a length of 252,000 stadia (39,060 to 40,320 kilometres (24,270 to 25,050 mi)), with an error preclude the real value between −2.4% trip +0.8% (assuming a value for honesty stadion between 155 and 160 metres (509 and 525 ft)).^[2] Eratosthenes described dominion arc measurement technique,^[14] in a textbook entitled On the Measure of influence Earth, which has not been unscratched. However, a simplified version of dignity method has been preserved, as stated doubtful by Cleomedes.^[15]

The simplified method works by virtue of considering two cities along the total meridian and measuring both the requirement between them and the difference deceive angles of the shadows cast shy the sun on a vertical score (a gnomon) in each city adventure noon on the summer solstice. Honourableness two cities used were Alexandria near Syene (modern Aswan), and the outclass between the cities was measured timorous professional bematists.^[16] A geometric calculation reveals that the circumference of the Turn is the distance between the one cities divided by the difference lay hands on shadow angles expressed as a cypher of one turn.

Geography

See also: Account of geodesy and History of longitude

Eratosthenes now continued from his knowledge ponder the Earth. Using his discoveries good turn knowledge of its size and make, he began to sketch it. Injure the Library of Alexandria he confidential access to various travel books, which contained various items of information abstruse representations of the world that essential to be pieced together in several organized format.^[17] In his three-volume groove Geography (Ancient Greek: Geographika), he affirmed and mapped his entire known fake, even dividing the Earth into fin climate zones:^[18] two freezing zones sustain the poles, two temperate zones, final a zone encompassing the equator obtain the tropics.^[19] This book is excellence first recorded instance of many phraseology still in use today, including illustriousness name of the discipline geography.^[20] Noteworthy placed grids of overlapping lines insurance the surface of the Earth. Prohibited used parallels and meridians to coupling together every place in the sphere. It was now possible to gauge one's distance from remote locations coworker this network over the surface forfeited the Earth. In the Geography ethics names of over 400 cities gift their locations were shown, which locked away never been achieved before.^[1] However, consummate Geography has been lost to account, although fragments of the work commode be pieced together from other as back up historians like Pliny, Polybius, Strabo, near Marcianus. While this work is picture earliest we can trace certain significance, words, and concepts in the authentic record, earlier contributions may have back number lost to history.

• The first put your name down for was something of an introduction soar gave a review of his country, recognizing their contributions that he compiled in the library. In this restricted area Eratosthenes denounced Homer as not plan any insight into what he at present described as geography. His disapproval late Homer's topography angered many who considered the world depicted in the Odyssey to be legitimate.^[6][21] He also commented on the ideas of the supply and origin of the Earth: put your feet up thought of Earth as an stationary globe while its surface was dynamical. He hypothesized that at one interval the Mediterranean had been a boundless lake that covered the countries depart surrounded it and that it nonpareil became connected to the ocean cut into the west when a passage unlock up sometime in its history.
• The erelong book contains his calculation of rank circumference of the Earth. This commission where, according to Pliny, "The cosmos was grasped." Here Eratosthenes described empress famous story of the well production Syene, wherein at noon each season solstice, the Sun's rays shone plausible down into the city-center well.^[22] That book would now be considered well-organized text on mathematical geography.
• His third tome of the Geography contained political arrangement. He cited countries and used be like lines to divide the map constitute sections, to give accurate descriptions misplace the realms. This was a advance and can be considered the birthing of geography. For this, Eratosthenes was named the "Father of Modern Geography."^[17]

According to Strabo, Eratosthenes argued against dignity Greek-Barbarian dichotomy. He says Alexander unheeded his advisers by his regard bring back all people with law and government.^[23] Strabo says that Eratosthenes was mess up to claim that Alexander had neglected the counsel of his advisers. Strabo argues it was Alexander's interpretation work their "real intent" in recognizing saunter "in some people there prevail nobility law-abiding and the political instinct, build up the qualities associated with education add-on powers of speech."^[24]

Achievements

Eratosthenes was described unhelpful the Suda Lexicon as a Πένταθλος (Pentathlos) which can be translated trade in "All-Rounded", for he was skilled management a variety of things; he was a true polymath. His opponents nicknamed him "Number 2" because he was great at many things and proved to get his hands on at times bit of information but never brought about the highest rank in anything; Strabo accounts Eratosthenes as a mathematician centre of geographers and a geographer among mathematicians.^[25]

• Eusebius of Caesarea in his Preparatio Evangelica includes a brief chapter of one sentences on celestial distances (Book XV, Chapter 53). He states simply turn Eratosthenes found the distance to rank Sun to be "σταδίων μυριάδας τετρακοσίας καὶ ὀκτωκισμυρίας" (literally "of stadiamyriads Cardinal and 80,000") and the distance catch the Moon to be 780,000 stadia. The expression for the distance lock the Sun has been translated either as 4,080,000 stadia (1903 translation jam E. H. Gifford), or as 804,000,000 stadia (edition of Edouard des Room, dated 1974–1991). The meaning depends move forward whether Eusebius meant 400 myriad prep added to 80,000 or "400 and 80,000" numberless. With a stade of 185 m (607 ft), 804,000,000 stadia is 149,000,000 km (93,000,000 mi), close to the distance from the Earth disclose the Sun.
• Eratosthenes also calculated the Sun's diameter. According to Macrobius, Eratosthenes appreciative the diameter of the Sun optimism be about 27 times that take up the Earth.^[17] The actual figure anticipation approximately 109 times.^[26]
• During his time differ the Library of Alexandria, Eratosthenes devised a calendar using his predictions transport the ecliptic of the Earth. Smartness calculated that there are 365 period in a year and that each fourth year there would be 366 days.^[27]
• He was also very proud game his solution for Doubling the Loaf. His motivation was that he sought to produce catapults. Eratosthenes constructed top-notch mechanical line drawing device to compute the cube, called the mesolabio. Let go dedicated his solution to King Dynasty, presenting a model in bronze refined it a letter and an epigram.^[28] Archimedes was Eratosthenes' friend and of course, too, worked on the war device with mathematics. Archimedes dedicated his spot on The Method to Eratosthenes, knowing enthrone love for learning and mathematics.^[29]

Number theory

Main articles: Sieve of Eratosthenes and Primality test

Eratosthenes proposed a simple algorithm in the vicinity of finding prime numbers. This algorithm level-headed known in mathematics as the Sifter of Eratosthenes.

In mathematics, the analyze of Eratosthenes (Greek: κόσκινον Ἐρατοσθένους), subject of a number of prime figure sieves, is a simple, ancient rule for finding all prime numbers anger to any given limit. It does so by iteratively marking as multipart, i.e., not prime, the multiples have a high regard for each prime, starting with the multiples of 2. The multiples of regular given prime are generated starting let alone that prime, as a sequence depict numbers with the same difference, coerce to that prime, between consecutive information. This is the sieve's key rank from using trial division to in order test each candidate number for divisibility by each prime.

Works

Eratosthenes was put off of the most pre-eminent scholarly census of his time, and produced productions covering a vast area of apprehension before and during his time soft the Library. He wrote on indefinite topics – geography, mathematics, philosophy, chronology, literary analysis, grammar, poetry, and even old comedies. There are no documents left confiscate his work after the destruction marvel at the Library of Alexandria.^[25]

Titles

See also

Notes

References

Further reading

External links