To the ancient Greek it meant land--not all land, but only a limited territory, in the centre of which he lived. His earth comprised simply the Persian Empire, Italy, Egypt and the borders of the Black and Mediterranean seas, besides his own country. Beyond these limits, the land extended indefinitely to an unknown distance--till it reached the borders of the great ocean which completely surrounded it.
To the members of this society the word "earth" suggests a very different idea. The term arouses in our minds the conception of an enormous globe suspended in empty space, one side in shadow and the other bathed in the rays of the sun. The outer surface of this globe consists of a uniform, unbroken ocean of air, enclosing another more solid surface (composed partly of land and partly of water), which teems with countless forms of animal and vegetable life. This is the earth of which geography gives _us_ a description.
To the ancients the earth was a flat plain, solid and immovable, and surrounded by water, out of which the sun rose in the east and into which it set in the west. To them "Geography" meant simply a description of the lands with which they were acquainted.
Herodotus, who lived about the year 450 B.C., transmitted to posterity an account of the world as it was known in his day. We look upon him as the father of geography as well as of history. He visited the known regions of the earth, and described accurately what he saw, thus laying the foundations of comparative geography.
About 300 years B.C., Alexander the Great penetrated into hitherto unknown regions, conquered India and Russia, and founded the Macedonian Empire. He sent a naval expedition to explore the coasts of India, accompanied by philosophers or learned men, who described the new countries discovered and the character of their inhabitants. This voyage may be considered as originating the science of Political Geography, or the geography of man.
About the year 200 B.C., Eratosthenes of Cyrene, the keeper of the Royal Library at Alexandria, became convinced, from experiments, that the idea of the rotundity of the earth, which had been advanced by some of his predecessors, was correct, and attempted to determine upon correct principles its magnitude. The town of Cyrene, on the river Nile, was situated exactly under the tropic, for he knew that on the day of the summer solstice, the sun's rays illuminated at noon the bottom of a deep well in that city. At Alexandria, however, on the day of the summer solstice, Eratosthenes observed that the vertical finger of a sun-dial cast a shadow at noon, showing that the sun was not there exactly overhead. From the length of the shadow he ascertained the sun's distance from the zenith to be 7° 12', or one-fiftieth part of the circumference of the heavens; from which he calculated that if the world was round the distance between Alexandria and Cyrene should be one-fiftieth part of the circumference of the world. The distance between these cities was 5000 stadia, from which he calculated that the circumference of the world was fifty times this amount, or 250,000 stadia. Unfortunately we are ignorant of the exact length of a stadium, so we have no means of testing the accuracy of his deduction. He was the founder of Mathematical Geography; it became possible through the labors of Eratosthenes to determine the location of places on the surface of the earth by means of lines corresponding to our lines of latitude and longitude.