II. ANAXAGORAS

It was part of the struggle between religion and science that the study of astronomy was forbidden by Athenian law at the height of the Periclean age.⁶ At Acragas Empedocles suggested that light takes time to pass from one point to another.⁷ At Elea Parmenides announced the sphericity of the earth, divided the planet into five zones, and observed that the moon always has its bright portion turned toward the sun.⁸ At Thebes Philolaus the Pythagorean deposed the earth from the center of the universe, and reduced it to the status of one among many planets revolving about a “central fire.”⁹ Leucippus, pupil of Philolaus, attributed the origin of the stars to the incandescent combustion and concentration of material “drawn onward in the universal movement of the circular vortex.”¹⁰At Abdera Democritus, pupil of Leucippus and student of Babylonian lore, described the Milky Way as a multitude of small stars, and summarized astronomic history as the periodical collision and destruction of an infinite number of worlds.¹¹ At Chios Oenopides discovered the obliquity of the ecliptic.^11a Nearly everywhere among the Greek colonies the fifth century saw scientific developments remarkable in a period almost devoid of scientific instruments.

But when Anaxagoras tried to do similar work at Athens he found the mood of the people and the Assembly as hostile to free inquiry as the friendship of Pericles was encouraging. He had come from Clazomenae about 480 B.C., at twenty years of age. Anaximenes so interested him in the stars that when someone asked him the object of life he answered, “The investigation of sun, moon, and heaven.”¹² He neglected his patrimony to chart the earth and the sky, and fell into poverty while his book On Naturewas acclaimed by the intelligentsia of Athens as the greatest scientific work of the century.

It carried on the traditions and speculations of the Ionian school. The universe, said Anaxagoras, was originally a chaos of diverse seeds (spermata), pervaded by a nous, or Mind, tenuously physical, and akin to the source of life and motion in ourselves. And as mind gives order to the chaos of our actions, so the World Mind gave order to the primeval seeds, setting them into a rotatory vortex,* and guiding them toward the development of organic forms.¹³ This rotation sorted the seeds into the four elements—fire, air, water, and earth—and separated the world into two revolving layers, an outer one of “ether,” and an inner one of air. “In consequence of this violent whirling motion, the surrounding fiery ether tore away stones from the earth, and kindled them into stars.”¹⁴ The sun and the stars are glowing masses of rock: “The sun is a red-hot mass many times larger than the Peloponnesus.”¹⁵ When their revolving motion wanes, the stones of the outer layer fall upon the earth as meteors.¹⁶ The moon is an incandescent solid, having on its surface plains, mountains, and ravines;¹⁷ it receives its light from the sun, and is of all heavenly bodies the nearest to the earth.¹⁸ “The moon is eclipsed through the interposition of the earth . . . the sun through the interposition of the moon.”¹⁹ Probably other celestial bodies are inhabited like the earth; upon them “men are formed, and other animals that have life; the men dwell in cities, and cultivate fields as we do.”²⁰ Out of the inner or gaseous layer of our planet successive condensations produced clouds, water, earth, and stones. Winds are due to rarefactions of the atmosphere produced by the heat of the sun; “thunder is caused by the collision of clouds, and lightning by their friction.”²¹ The quantity of matter never changes, but all forms begin and pass away; in time the mountains will become the sea.²² The various forms and objects of the world are brought into being by increasingly definite aggregations of homogeneous parts (homoiomeria)²³ All organisms were originally generated out of earth, moisture, and heat, and thereafter from one another.²⁴ Man has developed beyond other animals because his erect posture freed his hands for grasping things.²⁵

These achievements—the foundation of meteorology, the correct explanation of eclipses, a rational hypothesis of planetary formation, the discovery of the borrowed light of the moon, and an evolutionary conception of animal and human life—made Anaxagoras at once the Copernicus and Darwin of his age. The Athenians might have forgiven him these apergus had he not neglected his nous in explaining the events of nature and history; perhaps they suspected that this nous, like Euripides’ deus ex machina, was a device for saving the author’s skin. Aristotle notes that Anaxagoras sought natural explanations everywhere.²⁶ When a ram with a single horn in the center of its forehead was brought to Pericles, and a soothsayer interpreted it as a supernatural omen, Anaxagoras had the animal’s skull cleft, and showed that the brain, instead of filling both sides of the cranium, had grown upward towards the center, and so had produced the solitary horn.²⁷ He aroused the simple by giving a natural explanation of meteors, and reduced many mythical figures to personified abstractions.²⁸

The Athenians took him good-humoredly for a time, merely nicknaming him nous.²⁹ But when no other way could be found of weakening Pericles, Cleon, his demagogic rival, brought a formal indictment of impiety against Anaxagoras on the charge that he had described the sun (still to the people a god) as a mass of stone on fire; and pursued the case so relentlessly that the philosopher, despite Pericles’ brave defense of him, was convicted.* Having no taste for hemlock, Anaxagoras fled to Lampsacus on the Hellespont, where he kept himself alive by teaching philosophy.†When news was brought to him that the Athenians had condemned him to death, he said, “Nature has long since condemned both them and me.”³³ He died a few years later, aged seventy-three.

The backwardness of the Athenians in astronomy was reflected in their calendar. There was no general Greek calendar: every state had its own; and each of the four possible points for beginning a new year was adopted somewhere in Greece; even the months changed their names across frontiers. The Attic calendar reckoned months by the moon, and years by the sun.³⁴ As twelve lunar months made only 360 days, a thirteenth month was added every second year to bring the calendar into harmony with the sun and the seasons.³⁵ Since this made the year ten days too long, Solon introduced the custom of having alternate months of twenty-nine and thirty days, arranged into three weeks (dekades) of ten (occasionally nine) days each;³⁶ and as an excess of four days still remained, the Greeks omitted one month every eighth year. In this incredibly devious way they at last arrived at a year of 365 ¼ days.‡

Meanwhile a modest degree of progress was made in terrestrial science. Anaxagoras correctly explained the annual overflow of the Nile as due to the spring thaws and rains of Ethiopia.³⁸ Greek geologists attributed the Straits of Gibraltar to a cleaving earthquake, and the Aegean isles to a subsiding sea.³⁹ Xanthus of Lydia, about 496, surmised that the Mediterranean and the Red Sea were formerly connected at Suez; and Aeschylus noted the belief of his time that Sicily had been torn asunder from Italy by a convulsion of the earth.⁴⁰ Scylax of Caria (521-485) explored the whole coast of the Mediterranean and the Black Sea. No Greek seems to have dared so adventurous a voyage of discovery as that which the Carthaginian Hanno, with a fleet of sixty ships, led through Gibraltar some 2600 miles down the west coast of Africa (ca. 490). Maps of the Mediterranean world were common in Athens at the end of the fifth century. Physics, so far as we know, remained undeveloped, though the curvatures of the Parthenon show considerable knowledge of optics. The Pythagoreans, towards 450, announced the most lasting of Greek scientific hypotheses—the atomic constitution of matter. Empedocles and others expounded a theory of the evolution of man from lower forms of life, and described the slow advance of man from savagery to civilization.⁴¹