Leucippus

It is likely that Leucippus (fl. 440 BC) proposed the atomic system sometime around 440 to 430 BC thus he is contemporary with the other post-Eleatic thinkers Anaxagoras and Empedocles as well as Melissus.

Two books are attributed to Leucippus: On Mind and The Great World System (Makrokosmos). The Great World System was Leucippus principle work.

Leucippus is unanimously held to be founder of the Greek atomic theory. The uncertainty which prevails in the biographical notices of the first philosophers is strikingly illustrated by the conflicting accounts transmitted to us of the circumstances of his life.

Together, Leucippus and Democritus are often called the ‘early’ atomists, to distinguish them from their famous later successors, Epicurus and his school, who took over and developed their teaching.
Leucippus

Seleucus of Seleucia (born c. 190 BC; fl. c. 150 BC)

In the 2nd century BC Seleucus of Seleucia, an astronomer, flourished.

He was a Hellenized Babylonian astronomer who flourished a century after Aristarchus in the Seleucid Empire.

Seleucus adopted the heliocentric of Aristarchus and is said to have proved the heliocentric theory.

According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning. Seleucus may have even proved the double motion of the earth, that is rotation on its own axis and around the sun.

Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon’s position relative to the Sun.

A fragment of a work by Seleucus of Seleucia, who supported Aristarchus’ heliocentric model in the 2nd century BC, has survived in Arabic translation, which was referred to by Rhazes (b. 865).
Seleucus of Seleucia (born c. 190 BC; fl. c. 150 BC)