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*Eu)/docos) of Cnidus, the son of Aeschlines, lived about B. C. 366. He was, according to Diogenes Laertius, astronomer, geometer, physician, and legislator. It is only in the first capacity that his fame has descended to our day, and he has ore of it than can be justified by any account of his astronomical science now in existence. As the probable introducer of the sphere into Greece, and perhaps the corrector, upon Egyptian information, of the length of the year, he enjoyed a wide and popular reputation, so that Laertius, who does not even mention Hipparchus, has given the life of Eudoxus in his usual manner, that is, with the omission of all an astronomer would wish to know. According to this writer, Eudoxus went to Athens at the age of twenty-three (he had been the pupil of Archytas in geometry, and heard Plato for some months, struggling at the same time with poverty. Being dismissed by Plato, but for what reason is not stated, his friends raised some money, and he sailed for Egypt, with letters of recommendation to Nectanabis, who in his turn recommended him to the priests. With them he remained sixteen months, with his chin and eyebrows shaved, and there, according to Laertius, he urote the Octaeteris. Several ancient writers attribute to him the invention or introduction of an imiprovement upon the Octaeterides of his predecessors. After a time, he came back to Athens with a band of pupils, having in the mean time taught philosophy in Cyzicum and the Propontis : he chose Athens, Laertius says, for the purpose of vexing Plato, at one of whose symposia he introduced the fashion of the guests reclining in a semicircle; and Nicomachus (he adds), the son of Aristotle, reports him to have said that pleasure was a good. So much for Laertius, who also refers to some decree which was made in honour of Eudoxus, names his son and daughters, states him to have written good works on astronomy and geometry, and mentions the curious way in which the bull Apis told his fortune when he was in Egypt. Eudoxus died at the age of fifty-three. Phanocritus wrote a work upon Eudoxus (Athen. 7.276f.), which is lost.


The fragmentary notices of Eudoxus are numerous. Strabo mentions him frequently, and states (ii. p. 119, xvii. p. 806) that the observatory of Eudoxus at Cnidus was existing in his time, from which he was accustomed to observe the star Canopus. Strabo also says that he remained thirteen years in Egypt, and attributes to him the introduction of the odd quarter of a day into the value of the year. Pliny (Plin. Nat. 2.47) seems to refer to the same thing. Seneca (Qu. Nat. 7.3) states him to have first brought the motions of the planets (a theory on this subject) from Egypt into Greece. Aristotle (Aristot. Met. 12.8) states him to have made separate spheres for the stars, sun, moon, and planets. Archimedes (in Arenar.) says he made the dia. meter of the sun nine times as great as that of the moon. Vitruvius (9.9) attributes to him the invention of a solar dial, called ἀράχνη : and so on.

But all we positively know of Eudoxus is from the poem of ARATUS and the commentary of Hipparchus upon it. From this commentary we learn that Aratus was not himself an observer, but was the versifier of the Φαινόμενα of Eudoxus, of which Hipparchus has preserved fragments for comparison with the version by Aratus. The result is, that though there were by no means so many nor so great errors in Eudoxus as in Aratus, yet the opinion which must be formed of the work of the former is, that it was written in the rudest state of the science by an observer who was not very competent even to the task of looking at the risings and settings of the stars. Delambre (Hist. Astr. Anc. vol. i. p. 107) has given a full account of the comparison made by Hipparchus of Aratus with Eudoxus, and of both with his own observations. He cannot bring himself to think that Eudoxus knew anything of geometry, though it is on record that he wrote geometrical works, in spite of the praises of Proclus, Cicero, Ptolemy, Sextus Empiricus (who places him with Hipparchus), &c., &c. Eudoxus, as cited by Hipparchus, neither talks like a geometer, nor like a person who had seen the heavens he describes: a bad globe, constructed some centuries before his time in Egypt, might, for anything that appears, have been his sole authority. But supposing, which is likely enough, that he was the first who brought any globe at all into Greece, it is not much to be wondered at that his reputation should have been magnified. As to what Proclus says of his geometry, see EUCLEIDES.

Rejecting the Ὀκταετηρίς mentioned by Laertius, which was not a writing, but a period of time, and also the fifth book of Euclid, which one manuscript of Euclid attributes to Eudoxus (Fabric. Bibl. Graec. vol. iv. p. 12), we have the following works, all lost, which he is said to have written :

Mentioned by Proclus and Laertius, which is not, however, to be taken as the title of a work: Ὀργανική, mentioned by Plutarch:

Ἀστρονομία δι᾽ ὲπῶν, by Suidas: two books.

Ἐνοπτρον or Κάτοπτρον and Φαινόμενα mentioned by Hipparchus, and the first by an anonymous biographer of Aratus: Περὶ Θεῶν καὶ Κόσμου καὶ τῶν Μετεωρολογουμένων mentioned by Eudocia:

Γῆς Περίοδος, a work often mentioned by Strabo, and by many others, as to which Harless thinks Semler's opinion probable, that it was written by Eudoxus of Rhodes.

Further Information

Fabric. Bibl. Graec. vol iv. p. 10, &c.; Weidler, Hist. Astron.; D. L. 3.816-91; Delambre, Hist. de l'Astron. Anc. vol. i.; Hipparchus, Comment. in Aratum ;Böhmer, Dissertatio de Eudoxo Cnidio, Helmstad. 1715; Ideler, in the Abhandl. der Berliner Akad. d. Wissenschaft for the year 1828, p. 189, &c., and for the year 1830, p. 49, &c.; Letronne, Journal. d. Sav. 1840, p. 741, &c.

[A. DE M.]

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  • Cross-references from this page (2):
    • Aristotle, Metaphysics, 12.1073a
    • Pliny the Elder, Naturalis Historia, 2.47
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