<Ul> <Li> The first book was something of an introduction and gave a review of his predecessors, recognizing their contributions that he compiled in the library . In this book Eratosthenes denounced Homer as not providing any insight into what he now described as geography . His disapproval of Homer's topography angered many who believed the world depicted in the Odyssey to be legitimate . He also commented on the ideas of the nature and origin of the Earth: he had thought of Earth as an immovable globe; while on its surface was a place that was changing . He had hypothesized that at one time the Mediterranean was a vast lake that covered the countries that surrounded it; and had only become connected to the ocean to the west when a passage had opened up sometime in its history . </Li> <Li> In the second book is his discovery about the circumference of the Earth . This is where, according to Pliny, "The world was grasped ." Eratosthenes described his famous story of the well in Syene, described above . This book would now be considered a text on mathematical geography . </Li> <Li> His third book of the Geography contained political geography . He cited countries and used parallel lines to divide the map into sections, to give accurate descriptions of the realms . This was a breakthrough, and can be considered the beginning of geography . </Li> </Ul> <Li> The first book was something of an introduction and gave a review of his predecessors, recognizing their contributions that he compiled in the library . In this book Eratosthenes denounced Homer as not providing any insight into what he now described as geography . His disapproval of Homer's topography angered many who believed the world depicted in the Odyssey to be legitimate . He also commented on the ideas of the nature and origin of the Earth: he had thought of Earth as an immovable globe; while on its surface was a place that was changing . He had hypothesized that at one time the Mediterranean was a vast lake that covered the countries that surrounded it; and had only become connected to the ocean to the west when a passage had opened up sometime in its history . </Li> <Li> In the second book is his discovery about the circumference of the Earth . This is where, according to Pliny, "The world was grasped ." Eratosthenes described his famous story of the well in Syene, described above . This book would now be considered a text on mathematical geography . </Li> <Li> His third book of the Geography contained political geography . He cited countries and used parallel lines to divide the map into sections, to give accurate descriptions of the realms . This was a breakthrough, and can be considered the beginning of geography . </Li>

When did eratosthenes calculate the circumference of the earth