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  1. 1. ERATOSTHENES’ BIOGRAPHY Eratosthenes of Cyrene lived approximately in 275-195 BC. He was born in Cyrene which is now in Libya in North Africa. He studied philosophy in Cyrene with some philosophers, scholars and poets. He then spent some years studying in Athens. Although a brilliant scholar in so many fields, he was never considered to be the best in any subject. He was also called Mr. Beta since he always came second as far as his contributions to science were concerned, since he was a contemporary and friend of the great Archimedes. This is why people called him by the nickname of “Beta,” for the second letter in the Greek alphabet. Primarily a mathematician, a very important work of Eratosthenes was Platonicus which, among other topics, discussed the mathematics which are the basis of Plato's philosophy. Although this work is now lost, Platonicus studied the basic definitions of geometry and arithmetic, as well as covering such topics as music. Despite being lost to history, we know something of Eratosthenes’ work by the writings of others. Eutocius and other authors described the way Eratosthenes solved the problem of duplicating the cube. Eratosthenes later erected a column at Alexandria with an epigram inscribed on it relating to his own mechanical solution to the cube problem. Another area in which Eratosthenes is remembered is his work with prime numbers. Although his original writings are lost, he is remembered for his 'Sieve of Eratosthenes' which, in modified form, is still an important tool in number theory research Eratosthenes is probably best known for the surprisingly accurate measurement of the circumference of the Earth he made. Once again his treatise, On the measurement of the Earth, is now lost, however, some information about these calculations appear in works by other authors. He made a surprisingly accurate estimate of the earth's circumference. In the great library in Alexandria he read that a deep vertical well near Syene, in southern Egypt, was entirely lit up by the sun at noon once a year. Eratosthenes reasoned that at this time the sun must be directly overhead,
  2. 2. with its rays shining directly into the well. In Alexandria, almost north of Syene, he knew that the sun was not directly overhead at noon on the same day because a vertical object doesn’t cast a shadow when the light is directly overhead. quot;Well!quot; he thought to himself, quot;everyone knows the earth is flat! How then, could there be no shadow in Syene when there is a definite shadow in Alexandria?quot; Eratosthenes could now measure the circumference of the earth (sorry Columbus) by making two assumptions - that the earth is round and that the sun's rays are essentially parallel. Eratosthenes hired a friend of his to walk from Alexandria to Syene to mark the distance. His friend found the distance between the two places to be about 500 miles. With this information and his knowledge of geometry, Erastothenes determined the circumference of the earth to be approximately 25,000 miles. And we all know what has a circumference? Yes!! He proved that the earth was round. Erastosthenes had changed the world forever with his discovery, for this led many seafaring explorers to set sail in search of new and exciting trade routes. And we all know what happened after that. Eratosthenes’ other contributions to astronomy include measurements of the distances from the Earth to the moon and Earth to the sun and created a star map containing 675 stars. He also wrote a poem called “Hermes” which described the fundamentals of astronomy.
  3. 3. Eratosthenes also made major contributions to the science of Geography and, in about 240 BC, became the third librarian at Alexandria, in the library in a temple of the Muses called the Mouseion. The library is said to have contained hundreds of thousands of papyrus and vellum scrolls. Late in his life, he lost his sight. Filled with despair, that his vitality was gone, he starved himself to death at the age of 80. GLOSSARY:  Despite: A pesar de deep: profundo  Sieve of Eratosthenes: Criba de … well: pozo  Accurate: exacto treatise. Tratado  To cast: proyectar to hire: alquilar, contratar  Lead, led, led: guiar, dirigir vellum scrolls. pergaminos  Seafaring: navegante to starve: morir de hambre COMPREHENSION QUESTIONS ABOUT ERATHOSTENES’ BIOGRAPHY 1. Where was he born? 2. Why was he called BETA? 3. What type of contribution did he do to Mathematics? 4. What did people believe about the Earth? 5. Why exactly did he discover that the solar rays were parallel in Syene and Alexandria? 6. What did he prove? 7. What contributions did he make to astronomy? 8. You know that in Eratosthenes’ times, education was very different to what we have today. What areas of knowledge did he study and research on? Compare it with current university degrees.