Man's physical universe



The Greeks, from Thales to Ptolemy, Made Many Discoveries and

Formulated Theories That Were Accepted for Nearly Two

Thousand Years.

No doubt there were many thinkers among the primitive astronomers

of Chaldea, Babylonia, China, Egypt, and India; among the outstanding

thinkers known to history was Thales of Miletus, who died in

546 B.C. He has been called the founder of Greek astronomy. Thales

was a merchant, statesman, engineer, mathematician, and astronomer.

He taught the Greek sailors to guide their ships by the polar star and

observed the natural division of the year into four seasons by the

regular recurrence of the longest and shortest days of the year and of

the two intervening days when the days and nights were of equal length.

He successfully predicted an eclipse of the sun. He believed the stars

to be self-luminous bodies and the moonlight to be but a reflection from

the sun. He taught that the earth was a flat disk floating on water.

Anaximander, a contemporary of Thales, was the first man to recognize

that the heavens revolve around the polar star and to teach that

the visible dome of the sky is half of a complete sphere whose center is

the earth. For many centuries after his time the earth was considered

to be the center of the universe, Anaximander is also said to have introduced

into Greece the sundial, consisting of an upright rod (style, or

gnomon) on a horizontal ground.

Anaximenes (died 526 B.C.) thought that all matter was composed of

one primordial substance, water. When water became rarefied, it was

fire; when condensed, it was earth.

Pythagoras (died about 500 B.C.)

thought that there were four elements^

— earth, water, air, and fire — instead of only one and drew

his picture of the universe with this idea in mind. The earth was recognized

by him to be a sphere, whose rotation explained the apparent

rotation of the heavens.

It is unnecessary to recite all of the fanciful conceptions of the universe

developed by the early philosophers of Greece. Inasmuch as

they were not greatly troubled with the necessity of testing their

theories, it is a wonder that they did not go farther astray.

Socrates (died 399 B.C.), who regarded introspection as the only

worthy type of study, influenced men to turn their attention away from

the investigation of nature. His pupil, Plato (died 384 B.C.), condemned

experiment as an impious and base art.

The next Greek of great importance was Aristotle (died 322 B.C.),

who was one of the greatest organizers and generalizers the world has

ever known. So great was the encyclopedia of knowledge compiled by

him that he was looked upon as the final authority in many fields of

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