350s BC

Astronomy

Aristotle adds 29 more spheres to the system of Eudoxus, producing a complex theory involving 56 spheres that is largely rejected by later Greek astronomers (although revived in medieval times). His spheres are all in contact so that one moves the others, with the prime mover being either the sphere of stars or an unseen mover behind that sphere. See also 380 bce Astronomy. (See biography.)

Aristotle explains solar and lunar eclipses, and argues that the Sun, Moon, and Earth are all spherical. He also studies comets, but fails to recognize them as heavenly bodies. See also 432 bce Astronomy.

Greek astronomer Heracleides [b. Heraclea Pontus (Turkey), c. 388 bce, d. Athens, 315 bce] becomes the first person known to suggest that Earth rotates and that Venus and Mercury may orbit the Sun. See also 470 bce Astronomy; 270 bce Astronomy.

Aristotle dissects plants and animals and recognizes the need for classification, categorizing more than 500 species. He also studies the development of the embryo by observing unhatched birds. See also 500 bce Biology.

Aristotle describes image projection. Having observed that a partial eclipse of the Sun projects the Sun's image through small spaces between leaves of a tree, he experiments with using what amount to pinholes to project bright images onto screens. The same idea is behind the camera obscura and the pinhole camera.

Celtic chiefs begin building Maiden Castle in south Dorset, England, one of the great fortified earthworks of Neolithic Britain.

Aristotle proposes that fossils are accidental natural formations, a theory that remains popular for many centuries. He correctly describes the water cycle, but also thinks that earthquakes are caused by winds, thunder is caused by collisions between clouds, and lightning is the fire produced in the collision. See also 530 bce Earth science.

In Prior Analyticus and Posterior Analyticus, part of Organon, Aristotle expounds his ideas about logic and describes the syllogism.

Aristotle incorrectly considers the heart to be the center of intelligence. He identifies five senses common to all humans: sight, hearing, taste, smell, and touch. See also 450 bce Medicine & health; 300 bce Medicine & health.

Aristotle rejects atomism because it implies the existence of a vacuum. He describes motion as requiring a continued force. See also 430 bce Physics.

The geographer Syclax the Younger publishes the first Periplus ("coast pilot"), a guide to the ports and rivers of the Mediterranean world, giving distances between points, locations for fresh water, and other information useful to sailors. See also 300 bce Earth science.

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