Everything about Posidonius totally explained
Posidonius (
Greek: Ποσειδώνιος / Poseidonios) "of
Apameia" (ὁ Απαμεύς) or "of
Rhodes" (ὁ Ρόδιος) (ca.
135 BCE -
51 BCE), was a
Greek Stoic philosopher,
politician,
astronomer,
geographer,
historian and
teacher native to
Apamea,
Syria. He was acclaimed as the greatest
polymath of his age. None of his vast body of work can be read in its entirety today as it exists only in fragments.
Life
Posidonius (also spelled Poseidonius), nicknamed "the Athlete", was born to a
Greek These three categories for him were, in Stoic fashion, inseparable and interdependent parts of an organic, natural whole. He compared them to a living being, with physics the meat and blood, logic the bones and tendons which held the organism together, and ethics – the most important part – the soul.
Astronomy
Some fragments of his writings on astronomy survive through the treatise by
Cleomedes,
On the Circular Motions of the Celestial Bodies, the first chapter of the second book appearing to have been mostly copied from Posidonius.
Posidonius advanced the theory that the Sun emanated a vital force which permeated the world.
He attempted to measure the distance and size of the
Sun. In about
90 BCE Posidonius estimated the
astronomical unit to be
a0/
rE = 9893, which was still too small by half. In measuring the size of the Sun, however, he reached a figure larger and more accurate than those proposed by other Greek astronomers and
Aristarchus of Samos.
Posidonius also calculated the size and distance of the
Moon.
Posidonius constructed an
orrery, possibly similar to the
Antikythera mechanism. Posidonius's orrery, according to
Cicero, exhibited the diurnal motions of the sun, moon, and the five known planets.
Geography, ethnology and geology
Posidonius’s fame beyond specialized philosophical circles had begun, at the latest, in the eighties with the publication of the work "about the ocean and the adjacent areas". This work wasn't only an overall representation of geographical questions according to current scientific knowledge, but it served to popularize his theories about the internal connections of the world, to show how all the forces had an effect on each other and how the interconnectedness applied also to human life, to the political just as to the personal spheres. In this work, Posidonius detailed his theory of the effect on a people’s character by the climate, which included his representation of the "geography of the races". This theory wasn't solely scientific, but also had political implications -- his Roman readers were informed that the climatic central position of Italy was an essential condition of the Roman destiny to dominate the world. As a Stoic he did not, however, make a fundamental distinction between the civilized Romans as masters of the world and the less civilized peoples.
Posidonius measured the
Earth's circumference by reference to the position of the star
Canopus. As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at
Alexandria he saw it ascend as far as 7 1/2 degrees above the horizon (the arc between the latitude of the two locales is actually 5 degrees 14 minutes). Since he thought Rhodes was 5,000 stadia due north of Alexandria, and the difference in the star's elevation indicated the distance between the two locales was 1/48th of the circle, he multiplied 5,000 by 48 to arrive at a figure of 240,000 stadia for the circumference of the earth. While translating stadia into modern units of distance is problematic, as an ancient stadium could measure anywhere from about 157 to around 211 meters, it's generally thought that the stadium used by Posidonius was almost exactly 1/10 of a modern statute mile, near the middle of the ancient range. Thus Posidonius' measure of 240,000 stadia translates to 24,000 miles, not much short of the actual circumference of 24,901 miles.
Posidonius was informed in his approach to finding the earth's circumference by
Eratosthenes, who a century earlier used the elevation of the sun at different latitudes to arrive at a figure of 250,000 stadia (which he rounded to 252,000 so that it would be divisible by 60). As with Posidonius, Eratosthenes' stadium is thought to have equated to 1/10th of a mile, so that his measure translates to 25,000 (or 25,200) miles. Both men's figures for the earth's circumference were uncannily accurate, aided in part in each case by mutually compensating errors in measurement. However, Posidonius later revised his original calculation by correcting the distance between Rhodes and Alexandria to 3,750 stadia, resulting in a circumference of 180,000 stadia, or 18,000 miles.
Ptolemy discussed and favored this revised figure of Posidonius over Eratosthenes in his
Geographia, and during the
Middle Ages scholars divided into two camps regarding the circumference of the earth, identified with Eratosthenes' calculation on the one hand and Posidonius' 180,000-stadium measure on the other.
Like
Pytheas, Posidonius believed the
tide is caused by the
Moon. Posidonius was, however, wrong about the cause. Thinking that the Moon was a mixture of air and fire, he attributed the cause of the tides to the heat of the Moon, hot enough to cause the water to swell but not hot enough to evaporate it.
He recorded observations on both earthquakes and volcanoes, including accounts of the eruptions of the volcanoes in the
Aeolian Islands, north of
Sicily.
Meteorology
Posidonius in his writings on meteorology followed
Aristotle. He theorized on the causes of clouds, mist, wind, and rain as well as frost, hail, lightning, and rainbows.
Mathematics
In addition to his writings on geometry, Posidonius was credited for creating some mathematical definitions, or for articulating views on technical terms, for example 'theorem' and 'problem'.
History and tactics
In his
Histories, Posidonius continued the
World History of
Polybius. His history of the period 146 - 88 BCE is said to have filled 52 volumes. His
Histories continue the account of the rise and expansion of Roman dominance, which he appears to have supported. Posidonius didn't follow Polybius's more detached and factual style, for Posidonius saw events as caused by human psychology; while he understood human passions and follies, he didn't pardon or excuse them in his historical writing, using his narrative skill in fact to enlist the readers' approval or condemnation.
For Posidonius "history" extended beyond the earth into the sky; humanity wasn't isolated each in its own political history, but was a part of the cosmos. His
Histories were not, therefore, concerned with isolated political history of peoples and individuals, but they included discussions of all forces and factors (geographical factors, mineral resources, climate, nutrition), which let humans act and be a part of their environment. For example, Posidonius considered the climate of Arabia and the life-giving strength of the sun, tides (taken from his book on the oceans), and climatic theory to explain people’s ethnic or national characters.
Of Posidonius's work on tactics,
The Art of War, the Roman historian
Arrian complained that it was written 'for experts', which suggests that Posidonius may have had first hand experience of military leadership or, perhaps, utilized knowledge he gained from his acquaintance with
Pompey.
Reputation and influence
In his own era, his writings on almost all the principal divisions of philosophy made Posidonius a renowned international figure throughout the Graeco-Roman world and he was widely cited by writers of his era, including Cicero,
Livy,
Plutarch,
Strabo (who called Posidonius "the most learned of all philosophers of my time"), Cleomedes,
Seneca the Younger,
Diodorus Siculus (who used Posidonius as a source for his
Bibliotheca historia ("Historical Library"), and others. Although his ornate and rhetorical style of writing passed out of fashion soon after his death, Posidonius was acclaimed during his life for his literary ability and as a stylist.
Posidonius was the major source of materials on the
Celts of
Gaul and was profusely quoted by
Timagenes,
Julius Caesar, the Sicilian Greek
Diodorus Siculus, and the Greek geographer
Strabo.
Posidonius appears to have moved with ease among the upper echelons of Roman society as an ambassador from Rhodes. He associated with some of the leading figures of late republican Rome, including Cicero and Pompey, both of whom visited him in Rhodes. In his twenties, Cicero attended his lectures (77 BCE) and they continued to correspond. Cicero in his
De Finibus closely followed Posidonius's presentation of Panaetius's ethical teachings. Posidonius met Pompey when he was Rhodes's ambassador in Rome and Pompey visited him in Rhodes twice, once in 66 BCE during his campaign against the pirates and again in 62 BCE during his eastern campaigns, and asked Posidonius to write his biography. As a gesture of respect and great honor, Pompey lowered his
fasces before Posidonius's door. Other Romans who visited Posidonius in Rhodes were Velleius, Cotta, and
Lucilius.
Ptolemy was impressed by the sophistication of Posidonius's methods, which included correcting for the refraction of light passing through denser air near the horizon. Ptolemy's approval of Posidonius's result, rather than Eratosthenes's earlier and more correct figure, caused it to become the accepted value for the Earth's circumference for the next 1,500 years.
Posidonius fortified the Stoicism of the middle period with contemporary learning. Next to his teacher Panaetius, he did most, by writings and personal contacts, to spread Stoicism in the Roman world.
A century later, Seneca referred to Posidonius as one of those who had made the largest contribution to philosophy.
His influence on philosophical thinking lasted until the
Middle Ages, as is shown by citation in the
Suda, the massive medieval
lexicon.
At one time, scholars perceived Posidonius's influence in almost every subsequent writer, whether warranted or not. Today, Posidonius seems to be recognized as having had an inquiring and wide-ranging mind, not entirely original, but with a breadth of view that connected, in accordance with his underlying Stoic philosophy, all things and their causes and all knowledge into an overarching, unified world view.
The
Posidonius crater on the
Moon is named for him.
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