Geography Reference
In-Depth Information
On the other hand, the great philosopher also fell back on fairly simplistic reasoning. Aristotle thought
that the closer to the equator, the hotter the temperature. His “proof” lay in the black skin of Libyans who,
in Aristotle's thinking, had been seared by the sun. Life at the equator was not possible, in Aristotle's con-
ception, because it would be too hot there. Aristotle also believed in a natural balance that dictated the ex-
istence of a continent to the south of the equator equal to one north of the equator, introducing the concept
of the antipodes, or “opposite feet,” that lasted from Aristotle's time until the voyages of Captain Cook in
the mid-eighteenth century.
But three other so-called Greeks stand out because they all addressed Greek knowledge of the world in
separate topics, all with “geography” in the title.
The first of these was Eratosthenes (circa 276-194
BC
), actually a Libyan-born librarian who was the
first to use the word “geography” and who also managed to come up with a way to measure quite accur-
ately the circumference of the earth with little more than a shadow, a well, and some basic camel sense.
Eratosthenes was appointed chief of the library at Alexandria, where he controlled a collection of
more than a hundred thousand “books”—actually papyrus scrolls—containing the known world's collect-
ive knowledge. About two hundred fifty years before the birth of Christ, the Western world's most im-
portant city was Alexandria, in Egypt, the home of the renowned library started by Alexander the Great,
the young soldier from Macedon tutored by Aristotle. After Alexander's death, his heirs as rulers of Egypt
were the Ptolemies (the legendary Cleopatra among them). Under the three-hundred-year-long Ptolemy
dynasty, Alexandria became the world's preeminent center of scientific, mathematical, and literary studies,
as well as a rather seamy den of cutthroats drawn by the riches of the world that passed through the city.
It was, as one poet called it, the “house of Aphrodite” (goddess of love) with plenty of wine, wealth, fine
young men, and beautiful women. Makes you wonder how they got any work done.
One of Eratosthenes's greatest contributions seems simple enough, given the benefit of hindsight.
However, nobody else thought of it sooner, so Eratosthenes gets the credit for dividing the world by paral-
lel east-west and north-south lines, or meridians. He failed to lay these lines down at regular intervals and
instead used notable landmarks and prominent places such as Rhodes, Alexandria, the Pillars of Hercules
(Gibraltar), and the tip of the Indian Peninsula as the basis for dividing his world.
Hearing of a well in Syene (modern Aswan) where the sun's reflection could be seen in the water at
noon on June 21, the longest day of the year, Eratosthenes surmised that the sun was directly above the
earth at that moment. The Libyan librarian then made some interesting logical leaps. He believed that
Syene was due south of Alexandria on the same meridian (or longitudinal line, the imaginary north-south
running lines on the map). By measuring the shadow cast by an obelisk in Alexandria at the same moment
there was no shadow in Syene, Eratosthenes computed the length of two sides of a triangle—the length
of the shadow and the height of the obelisk. With that information and some basic geometry, Eratosthenes
figured the angle of the triangle, and with that figure determined the degree that the sun was from directly
overhead. That proved to be 7˚12, which is approximately equal to one fiftieth of a circle's 360 degrees.
Knowing this, Eratosthenes further reasoned that if he knew the distance from Syene to Alexan-
dria—which would equal the third side of his triangle connecting the sun, Alexandria, and Syene—he
could simply multiply that distance by fifty to get the approximate size of the earth. Enter the camels.
Eratosthenes learned that it took a camel caravan fifty days to make the trip from Syene to Alexandria.
Using ancient EPA camel standards of 100 stadia per day (stadia is an ancient measurement that related
to the size of a Greek race course), the clever librarian came up with a distance of 5,000 stadia from
Syene to Alexandria. Multiplying that by 50 gave Eratosthenes an earth circumference of 250,000 stadia.
Using various estimates of modern equivalents, his earth measured about 25,000 miles—very near its ac-
tual measurement at the poles of 24,860 miles. Given the number of small mistakes involved, all of which
