The groundwork is being laid for centuries of speculation, myth, and misconception. The equatorial zone is so hot as to be uninhabitable and impassable the two polar zonesĪre so cold as to be uninhabitable but between these two dreadful regions there is a northern and a southern temperate zone where life is supportable. There are five zones of climate in Mela's world.
This is the land of the Antichthones-the people of the opposite world. According to Mela, the northern land mass of Europe, Asia, and Africa is separated by an equatorial ocean from a large who had divided the world into climatic zones) are all incorporated. (a Greek philosopher of the sixth century B.C. Here a Roman geographer, Pomponius Mela, is borrowing from the works of the Greeks to produce a Latin geography, De situ orbis. And so begins, with this imaginative experiment, the science of geodesy-the science of Earth measurement.Ī quick spin of the globe and the scene shifts to Spain during the first century A.D. Thus the distance between Alexandria and Syene is one-fiftieth of the earth'sĬircumference (50x5,000=250,000 stadia, or 25,000 miles)-very close to the actual polar circumference of 24,860 miles. The angle is nearly 7 1/2 degrees-about one-fiftieth of a circle. When Eratosthenes bends down to measure the length of the shadow, he is measuring the size of the Earth. To the obelisk, he will be able to calculate the Earth's circumference.
Knowing that the Sun on the same day in Alexandria does cast a shadow at noon, Eratosthenes reasons that by measuring the shadow cast by a vertical obelisk near the Museum in Alexandria, then calculating the angle of the Sun's rays Of Alexandria and some fifty days' camel journey away (about 5,000 stadia), Eratosthenes knows of a deep well where the Sun, at noon on the day of the summer solstice, shines directly down the well shaft without casting a shadow. The instruments for this measurement are ingenious: the Sun, a deep well, and a vertical obelisk. InĪn experiment elegant in its simplicity, Eratosthenes sets about calculating the circumference of the Earth. Such theories, perhaps, the young Alexander had heard a few years earlier when Aristotle had been his tutor at the Macedonian court.īut what of the size of this sphere? A century after Aristotle, in 240 B.C., a brilliant polymath, Eratosthenes, is appointed chief librarian of the Museum at Alexandria-the most cosmopolitan city and center of learning in the Mediterranean world. Mass in the south to counterbalance the land mass of the north. "The sphericity of the Earth," Aristotle concludes, "is proved by the evidence of our senses." It follows-due to that sense of balance, order, and symmetry beloved of the Greeks-that there must also be a land Aristotle's reasons are based on observed fact: the constellations change as a person travels north or south, and during a lunar eclipse the shadow of the Earth that falls on the Moon is alwaysĬurved. and, in the shaded walkways of the Lyceum in Athens, Aristotle is strolling with his students and discussing what is so obvious to the intellectually curious-the spherical nature of the Earth, as opposed to the flat-discĮarth of the ancient Homeric Greeks. Journals of Captain James Cook, 21 February 1775 That there may be a Continent or large tract of land near the Pole, I will not deny, on the contrary I am of opinion there is. The intention of the Voyage has in every respect been fully Answered, the Southern Hemisphere sufficiently explored and a final end put to the searching after a Southern Continent, which has at times ingrossed the attention of some of the Maritime Powersįor near two Centuries past and the Geographers of all ages.