Who was Dionysodorus of Melos?

Question

I am trying to find information about Dionysodorus of Melos. Although he is mentioned by ancient writers, Wikipedia seems to ignore his existence, because it mentions three men by the name Dionysodorus, but describes none of them as being from Melos. I wonder what is going on. Can anyone please help me shed some light on this mystery?

Wikipedia mentions the following 3 people by the name Dionysodorus:

Dionysodorus of Chios (5th century BCE sophist)

The Wikipedia entry about Dionysodorus of Chios says that he was a sophistic philosopher and teacher of martial arts, generalship, and oration. It says that he is mentioned by Plato as having been born on Chios and as having lived in Thurii (modern-day Italy) and then Athens. Wikipedia also says that an individual named Dionysodorus is mentioned by Lysias, who potentially matches the sophist on several biographical details, and was a general and taxiarch who supported the democracy. Chios is an island in the north-east Aegean sea.

Dionysodorus of Caunus (3rd century BCE mathematician)

The Wikipedia entry for Dionysodorus of Caunus says that he is remembered for solving the cubic equation by means of the intersection of a rectangular hyperbola and a parabola. Caunus was a Greek city in the south-western corner of modern-day Turkey.

Dionysodorus of Amaseia (1st century CE mathematician)

The Wikipedia entry for Dionysodorus of Amaseia says that according to Pliny the Elder, he calculated the circumference of the Earth. Amaseia was a Greek city located in the north-east of modern-day Turkey.

Wikipedia says that there is often confusion between Dionysodorus of Amaseia and Dionysodorus of Caunus, and states that Strabo differentiates between the two mathematicians.

In his "Geography", Strabo writes:

"Now the territory of Amisus extends to this point; and the city has produced men noteworthy for their learning, Demetrius, the son of Rhathenus, and Dionysodorus, the mathematicians, the latter bearing the same name as the Melian geometer, and Tyrannion the grammarian, of whom I was a pupil." Strabo 12c

("Melian" means "of Melos". Melos is an island in the Cyclades, also known as Milos.) (Amisus seems to be related to Amaseia.)

So, what we see here is that contrary to Wikipedia, Strabo does not differentiate between Dionysodorus of Amaseia and Dionysodorus of Caunus; instead, he differentiates between Dionysodorus of Amaseia and Dionysodorus of Melos.

In book II of his work "The Natural History", Pliny the Elder has a paragraph about Dionysodorus. He states that he was a native of Melos, and in an arcane story which blurs the line between fact and fable, he attributes to Dionysodorus a measurement of the Earth's radius as 42000 stadia, which is roughly 6.5 thousand km, remarkably close to the actual number which is 6371 km. (Funny fact: from a radius of 42000 stadia, Pliny goes on to calculate Earth's circumference as 252000 stadia, which sadly means that he is under the impression that π is 3 instead of 3.14159... I thought that only Roman legionaries were so daft.) (Sources: Tufts/Perseus and Attalus )

So, what we see here is that again, contrary to Wikipedia, Pliny the Elder does not attribute the calculation of the Earth's radius to Dionysodorus of Amaseia, he attributes it to Dionysodorus of Melos.

What is going on here?

Answer 1

Pauly's Realencyclopädie has 24 people of that name, among them a mathematician from "Amisene" (sic, its capital is Amisos, nowadays known as Samsun) and a geometer from Melos. No person from Amaseia is mentioned. (translated with DeepL.com)

19 From the Pontic landscape of Amisene (whose capital was Amisos), Strabo XII 548 as a μαθηματικὸς ἄξιος μνήμης κατὰ παιδείαν. This D., not the one of the same name mentioned by Strabo in the same place and by Pliny Naturalis Historia II 248, wrote contributions to the Archimedean investigations on conic sections, from which Eutocios (on Archimedes' περὶ σφαίρας καὶ κυλίνδρου 180ff. Heib.) communicates the solution found by D. to the problem of cutting a sphere through a plane in such a way that the segments are in a given relationship to each other. Hence the note in Vitruvius IX 9, 1 D. conum (reliquit). On the method he followed in his proof, see Cantor Vorlesungen über die Geschichte der Mathemathik I² 383. Zeuthen Die Lehre von den Kegelschnitten im Altertum 250. Susemihl Die Geschichte der griechischen Litteratur in der Alexandrinerzeit I 762, 252. 763. He also wrote a book περὶ τῆς σπείρας, from which Hero Metrica II 13 (128, 3 Schöne) quotes a sentence. Schmidt Jahresber. CVΙΙΙΙ (1901) 62. As can be seen from Eutocius op. cit. 152, 20-154, 3, D. wrote before the mathematician Diocles, and is therefore dated to the 2nd cent. bc. BC or at the latest at the beginning of the 1st century.

20 Geometer from Melos according to Strabo XII 548. The report of Pliny Naturalis Historia II 248 shows that the question of the size of the earth occupied him until his old age. Following Eratosthenes, he assumed the circumference of the earth to be 252,000 stadia and, by assuming the circumference of the circle to be 3 diameters = 6 radii, estimated the distance from the surface to the centre of the earth to be 42,000 stadia. Pliny found this calculation in the source he used. However, given the brevity of the report, it is impossible to make a reliable judgement about the mystification that D. attempted at the end of his life according to the same source. A few days after his burial, a letter is said to have been found on his tombstone (which, of course, had been secretly laid down by a confidant following a commission given to him during his lifetime), which was addressed to the gods in heaven and contained the news that the writer had already travelled 42,000 stages to the centre of the earth. His heirs were female relatives; he probably wanted to play a trick on them in the expectation that their credulity could be trusted. The epoch of D. cannot be dated more precisely than between Eratosthenes and Strabo, roughly between 240 and 25 BC. Hoffmann's assumption in Marcian Periplus maris externae I 4 (Geographi graeci minores I 519 Müller) that D. is identical with the Dionysius, the son of Diogenes, mentioned there, can first of all be based on the manuscipt tradition διόνυσος, whose author could possibly have overlooked a dash placed over the end of the form of the name, indicating Διονυσόδωρος. Then we would have only one D. instead of two authors with similar names who followed Eratosthenes in determining the circumference of the earth. However, the Eratosthenes approach, later also adopted by Hipparchus, had general validity until Poseidonius, and among the countless who followed it there may very well have been a scholar in addition to the Melian D., whose form of name was certainly rightly produced as Διονύσιος (instead of the handwritten διόνυσος).

Another attempt to navigate the different persons by that name is the article on Dionysodorus by Ivor Bulmer-Thomas from the Dictionary of Scientific Biography. He cites Wilhelm Schmidt, "Über den griechischen Mathematiker Dionysodoros." Bibliotheca mathematica, 3rd Series, Vol. 4, 1903, pp. 321-325, that after the finding of a text in the Herculanean scrolls, the mathematician described by Eutocios seems to be identical to Dionysodorus of Caunus, and different to the one mentioned by Strabo "from Amisene" (Ἀμισηνή), and none of them is the geometer from Melos.

After all that, I suspect that the errors of the Wikipedia article already start with confusing the Pontian cities of Amaseia and Amisos.