MATHEMATICIAN, PHYSICIST

Life
Cleanthes was born in Assos, not far from Troy. His family was poor, and before he devoted himself to science he earned his living as a professional wrestler. He studied in Athens with Zeno of Citium, eventually succeeding him as the head of the Stoic School (262 - 232 BC). He is cited by Diogenes Laertius, Plutarch, Clement of Alexandria and Stobaeus. Echoes of his teachings may be detected in the writings of Aratus, Cicero, Dion, St John Chrysostom and St Paul. He wrote about 50 books, of which only fragments survive; the full list of titles is given by Diogenes Laertius.


Work
His principal works are:

"On sensation"

"On passion": 2 books.

"On the interpretation of Heracleitus": 4 books. This is his longest work

"In reply to Democritus": A study of problems in physics.

"On time": Time is defined as a dimension "of the movement of the world".

"In reply to Aristarchus": Polemic against the heliocentric system.

Cleanthes held fire to be the active and passive first principle and cause. He identified fire with the "uncreated matter and the divine". Natural changes were produced by the motion of the universe, which moved from the centre outwards. This universal motion he called "tone". As the motion proceeds towards the perimeter, "fire becomes water". "The sun is the lord of the universe, which feeds it and gives it life".