M. Boeckh also (in his recent publication, Ueber die vierjährigen Sonnenkreise der Alten, vorzüglich den Eudoxischen, Berlin, 1863) has given an account of the life and career of Eudoxus, not with reference to his theory of concentric spheres, but to his Calendar and Lunisolar Cycles or Periods, quadrennial and octennial. I think Boeckh is right in placing the voyage of Eudoxus to Egypt at an earlier period of the life of Eudoxus; that is, about 378 B.C.; and not in 362 B.C., where it is placed by Letronne and others. Boeckh shows that the letters of recommendation from Agesilaus to Nektanebos, which Eudoxus took with him, do not necessarily coincide in time with the military expedition of Agesilaus to Egypt, but were more probably of earlier date. (Boeckh, p. 140-148.)
Eudoxus lived 53 years (406-353 B.C., about); being born when Plato was 21, and dying when Plato was 75. He was one of the most illustrious men of the age. He was born in poor circumstances; but so marked was his early promise, that some of the medical school at Knidus assisted him to prosecute his studies — to visit Athens and hear the Sophists, Plato among them — to visit Egypt, Tarentum (where he studied geometry with Archytas), and Sicily (where he studied τὰ ἰατρικὰ with Philistion). These facts depend upon the Πίνακες of Kallimachus, which are good authority. (Diog. L. viii. 86.)
After thus preparing himself by travelling and varied study, Eudoxus took up the profession of a Sophist, at Kyzikus and the neighbouring cities in the Propontis. He obtained great celebrity, and a large number of pupils. M. Boeckh says, “Dort lebte er als Sophist, sagt Sotion: das heisst, er lehrte, und hielt Vortrage. Dasselbe bezeugt Philostratos.”
I wish to call particular attention to the way in which M. Boeckh here describes a Sophist of the fourth century B.C. Nothing can be more correct. Every man who taught and gave lectures to audiences more or less numerous, was so called. The Platonic critics altogether darken the history of philosophy, by using the word Sophist with its modern associations (and the unmeaning abstract Sophistic which they derive from it), to represent a supposed school of speculative and deceptive corruptors.
Eudoxus, having been coldly received when young and poor by Plato, had satisfaction in revisiting Athens at the height of his reputation, accompanied by numerous pupils — and in showing himself again to Plato. The two then became friends. Menæchmus and Helikon, geometrical pupils of Eudoxus, received instruction from Plato also; and Helikon accompanied Plato on his third voyage to Sicily (Plato, Epist. xiii. p. 360 D; Plut. Dion, c. 19). Whether Eudoxus accompanied him there also, as Boeckh supposes, is doubtful: I think it improbable.
Eudoxus ultimately returned to his native city of Knidus, where he was received with every demonstration of honour: a public vote of esteem and recognition being passed to welcome him. He is said to have been solicited to give laws to the city, and to have actually done so: how far this may be true, we cannot say. He also visited the neighbouring prince Mausôlus of Karia, by whom he was much honoured.
We know from Aristotle, that Eudoxus was not only illustrious as an astronomer and geometer, but that he also proposed a theory of Ethics, similar in its general formula to that which was afterwards laid down by Epikurus. Aristotle dissents from the theory, but he bears express testimony, in a manner very unusual with him, to the distinguished personal merit and virtue of Eudoxus (Ethic. Nikom. x. 3, p. 1172, b. 16).
[25] Respecting Eudoxus, see Diog. L. viii. 86-91. As the life of Eudoxus probably extended from about 406-353 B.C., his first visit to Athens would be about 383 B.C., some three years after Plato commenced his school. Strabo (xvii. 806), when he visited Heliopolis in Egypt, was shown by the guides certain cells or chambers which were said to have been occupied by Plato and Eudoxus, and was assured that the two had passed thirteen years together in Egypt. This account deserves no credit. Plato and Eudoxus visited Egypt, but not together, and neither of them for so long as thirteen years. Eudoxus stayed there sixteen months (Diog. L. viii. 87). Simplikius, Schol. ad Aristot. De Cœlo, p. 497, 498, ed. Brandis, 498, a. 45. Καὶ πρῶτος τῶν Ἑλλήνων Εὔδοξος ὁ Κνίδιος. ὡς Εὔδημός τε ἐν τῷ δευτέρῳ τῆς Ἀστρολογικῆς Ἰστορίας ἀπεμνημόνευσε καὶ Σωσιγένης παρὰ Εὐδήμου τοῦτο λαβὼν, ἅψασθαι λέγεται τῶν τοιούτων ὑποθέσεων· Πλάτωνος, ὡς φησι Σωσιγένης, πρόβλημα τοῦτο ποιησαμένου τοῖς περὶ ταῦτα ἐσπουδακόσι — τίνων ὑποτεθείσων ὁμαλῶν καὶ τεταγμένων κινήσεων διασωθῇ τὰ περὶ τὰς κινήσεις τῶν πλανωμένων φαινόμενα. The Scholion of Simplikius, which follows at great length, is exceedingly interesting and valuable, in regard to the astronomical theory of Eudoxus, with the modifications introduced into it by Kallippus, Aristotle, and others. All the share in it which is claimed for Plato, is, that he described in clear language the problem to be solved: and even that share depends simply upon the statement of the Alexandrine Sosigenes (contemporary of Julius Cæsar), not upon the statement of Eudemus. At least the language of Simplikius affirms, that Sosigenes copied from Eudemus the fact, that Eudoxus was the first Greek who proposed a systematic astronomical hypothesis to explain the motions of the planets — (παρ’ Εὐδήμου τοῦτο λαβών) not the circumstance, that Plato propounded the problem afterwards mentioned. From whom Sosigenes derived this last information, is not indicated. About his time, various fictions had gained credit in Egypt respecting the connection of Plato with Eudoxus, as we may see by the story of Strabo above cited. If Plato impressed upon others that which is here ascribed to him, he must have done so in conversation or oral discourse — for there is nothing in his written dialogues to that effect. Moreover, there is nothing in the dialogues to make us suppose that Plato adopted or approved the theory of Eudoxus. When Plato speaks of astronomy, either in the Republic, or in Leges, or in Epinomis, it is in a totally different spirit — not manifesting any care to save the astronomical phenomena. Both Aristotle himself (Metaphys. A. p. 1073 b.) and Simplikius, make it clear that Aristotle warmly espoused and enlarged the theory of Eudoxus. Theophrastus, successor of Aristotle, did the same. But we do not hear that either Speusippus or Xenokrates (successor of Plato) took any interest in the theory. This is one remarkable point of divergence between Plato and the Platonists on one side — Aristotle and the Aristotelians on the other — and much to the honour of the latter: for the theory of Eudoxus, though erroneous, was a great step towards improved scientific conceptions on astronomy, and a great provocative to farther observation of astronomical facts.
Though Plato demanded no money as a fee for admission of pupils, yet neither did he scruple to receive presents from rich men such as Dionysius, Dion, and others.[26] In the jests of Ephippus, Antiphanes, and other poets of the middle comedy, the pupils of Plato in the Academy are described as finely and delicately clad, nice in their persons even to affectation, with elegant caps and canes; which is the more to be noticed because the preceding comic poets derided Sokrates and his companions for qualities the very opposite — as prosing beggars, in mean attire and dirt.[27] Such students must have belonged to opulent families; and we may be sure that they requited their master by some valuable present, though no fee may have been formally demanded from them. Some conditions (though we do not know what) were doubtless required for admission. Moreover the example of Eudoxus shows that in some cases even ardent and promising pupils were practically repelled. At any rate, the teaching of Plato formed a marked contrast with that extreme and indiscriminate publicity which characterised the conversation of Sokrates, who passed his days in the market-place or in the public porticoes or palæstræ; while Plato both dwelt and discoursed in a quiet residence and garden a little way out of Athens. The title of Athens to be considered the training-city of Hellas (as Perikles had called her fifty years before), was fully sustained by the Athenian writers and teachers between 390-347; especially by Plato and Isokrates, the most celebrated and largely frequented. So many foreign pupils came to Isokrates that he affirms most of his pecuniary gains to have been derived from non-Athenians. Several of his pupils stayed with him three or four years. The like is doubtless true about the pupils of Plato.[28]