![]() Early Mesopotamian maps showed the world as a flat disk floating in the ocean. ![]() Belief in a flat Earth is found in the oldest writings. The idea of a flat Earth is that the surface of the Earth is flat (a plane). This kind of medieval mappa mundi illustrates only the reachable side of a round Earth. 15th century adaptation of a T and O map. So Eratosthenes’ first assumption is based on a map which he constructed using the wealth of knowledge available at the library of Alexandria. The main meridian in this map runs directly through several cities, including Alexandria and Syene. Using these two perpendicular main lines, Eratosthenes divided the map into rectangular regions he called seals, which could then be used to geometrically calculate any distance in the known world – hence the term “mathematical geography”. The map featured a main “parallel”, running east to west through the city of Rhodes, and a main meridian, running north and south through Rhodes. He examined countless texts, compiling records of measured distances and comparing various accounts of similarities in flora, fauna, climate, astronomical observations, local peoples, etc. Using the tremendous amount of information available to him at the great library in Alexandria, Eratosthenes sought to correct the traditional Greek map of the world. How does Eratosthenes justify this assumption?īefore his famous calculation of the Earth’s circumference, Eratosthenes attempted the earliest known scientific construction of a map based on mathematical geography. ![]() Now the geometrical argument takes place in two dimensions (the plane), rather than in three. If Alexandria and Syene both lie on the same meridian, Eratosthenes is guaranteed that two cities and the center of the Earth are all contained in the same plane. The plane of any meridian bisects the Earth. ![]() That Alexandria and Syene lie on the same meridian.Ī meridian is an imaginary circle on the Earth’s surface which passes through both the north and south poles. ![]()
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