Dionysodorus

Dionysodorus of Caunus (c. 250 BC – c. 190 BC) was an ancient Greek mathematician.

Life and work

Little is known about the life of Dionysodorus. Pliny the Elder writes that Dionysodorus was from Caunus, not to be confused with another Dionysodorus from Pontus who was mentioned by Strabo.

Dionysodorus is remembered for solving the cubic equation by means of the intersection of a rectangular hyperbola and a parabola.Eutocius credits Dionysodorus with the method of cutting a sphere into a given ratio, as described by him.Heron mentions a work by Dionysauras entitled On the Tore, in which the volume of a torus is calculated and found to be equal to the area of the generating circle multiplied by the circumference of the circle created by tracing the center of the generating circle as it rotates about the torus's axis of revolution. Dionysodorus used Archimedes' methods to prove this result.

It is also likely that this Dionysodorus invented the conical sundial. Pliny says that he had an inscription placed on his tomb, addressed to the world above, stating that he had been to the centre of the earth and found it 42 thousand stadia distant. Pliny calls this a striking instance of Greek vanity; but this figure compares well with the modern measurement.

Dionysodorus (sophist)

Dionysodorus (Greek: Διονυσόδωρος, Dionusódōros, c. 430 – late 5th century or early 4th century BCE) was an ancient Greek sophistic philosopher and teacher of martial arts, generalship, and oration. Closely associated with his brother and fellow sophist Euthydemus, he is depicted in the writing of Plato and Xenophon.

Life

Plato's Euthydemus, which features Dionysodorus and Euthydemus as prominent interlocutors, states that the brothers were born on the Aegean island of Chios before relocating as colonists to Thurii in Magna Graecia of modern-day Italy. After being exiled from Thurii, perhaps in 413, they came to Athens. According to Socrates in the Euthydemus, the two taught fighting in armor and legal oration before developing an interest in sophism. Xenophon's Memorabilia further attributes the teaching of generalship to Dionysodorus specifically.

Additionally, an individual named Dionysodorus appears in Lysias' Against Agoratus speech, who potentially matches the sophist on several biographical details. This Dionysodorus was a general and Taxiarch who supported the democracy; if the general and sophist are one and the same, Dionysodorus may have become a naturalized Athenian citizen along with many other foreign residents before the Battle of Arginusae.