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1050

DIOPHANTUS.

rius Gracchus, nor with the Diophanes whom Varro mentions. (Jacobs, xiii. p. 886.) [P. S.J

DIOPHANTUS (AioQavros). 1. A native of Arabia, who however lived at Athens, where he was at the head of the sophistical school. He was a contemporary of Proaeresius, whom he sur­vived, and whose funeral oration he delivered in A. d, 368. (Eunapius, Diopliant. p. 127, &c., Proaeres. p. 109.)

2. An Attic orator and contemporary of Demos­thenes, with whom he opposed the Macedonian party. He is mentioned as one of the most emi­nent speakers of the time. (Dem. de Fals. Leg. pp. 368, 403, 436, c. Lept. p. 498 ; Harpocrat. and Suid. s. v. MeAcewrros.) Reiske, in the Index to Demosthenes, believes him to be the same as the author of the psephisma mentioned by Demosthenes (de Fals. Leg. p. 368), and also identical with the one who, according to Diodorus (xvi. 48), assisted the king of Persia in his Egyptian war, in b. c. 350.

3. Of Lacedaemon, is quoted by Fulgentius (MyihoL i. 1) as the author of a work on Antiqui­ties, in fourteen books, and on the worship of the gods. Whether he is the same as the geographer, Diophantus, who wrote a description of the north­ern countries (Phot. Bibl. Cod. 250, p. 454, b.), which is also quoted by Stephanus of Byzantium (s. v. "Agtot), or the Diophantus who wrote a work TroAm/ca (Steph. Byz. s. v. Aigvcrnjfoi), cannot be decided.

4. A slave of Straton, who was manumitted by the will of his master. (Diog. Laert. v. 63.) He seems to be the same as the Diophantus mentioned in the will of Lycon. (Id. v. 71.)

5. Of Syracuse, a Pythagorean philosopher, who seems to have been an author, for his opinion on the origin of the world is adduced by Theodoretus. (TherapAv. p. 795.) [L. S.]

DIOPHANTUS (Ai(tyaz/ros), an Athenian co­ mic poet of the new comedy. (Antiatticista, p. 115, 21 : (ftepeiv rdv oivov znl rov vijtyetv. Aiocpavros WleTotKiiofjL&ip.) [P. S.]

DIOPHANTUS (A«tywros), of Alexandria, the only Greek writer on Algebra. His period is wholly unknown, which is not to be wondered at if we consider that he stands quite alone as to the subject which he treated. But, looking at the im­probability of all mention of such a writer being omitted by Proclus and Pappus, we feel strongly in­clined to place him towards the end of the fifth cen­tury of our era at the earliest. If the Diophantus, on whose astronomical work (according to Suidas) Hypatia wrote a commentary, and whose arith­metic Theon mentions in his commentary on the Almagest, be the subject of our article, he must have lived before the fifth century: but it would be by no means safe to assume this identity. Abulpharagius, according to Montucla, places him at a. d. 365. The first writer who mentions him, (if it be not Theon) is John, patriarch of Jerusa­lem, in his life of Johannes Damascenus, written in the eighth century. It matters not much where we place him, as far as Greek literature is concern­ed : the question will only become of importance when we have the means of investigating whether or not he derived his algebra, or any of it, from an Indian source. Colebrooke, as to this matter, is content that Diophantus should be placed in the fourth century. (See the Penny Cyclopaedia, art. Viya Ganita.}

DIOPHANTUS.

It is singular that, though his date is uncertain to a couple of centuries at least, we have some rea­son to suppose that he married at the age of 33, and that in five years a son was born of this marriage, who died at the age of 42, four years before his father: so that Diophantus lived to 84. Bachet, his editor, found a problem proposed in verse, in an unpublished Greek anthology, like some of those which Diophantus himself proposed in verse, and composed in the manner of an epitaph. The un­known quantity is the age to which Diophantus lived, and tne simple equation of condition to which it leads gives, when solved, the preceding informa­tion. But it is just as likely as not that the maker of the epigram invented the dates.

When the manuscripts of Diophantus came to light in the 16th century, it was said that there were thirteen books of the ' Arithmetica :' but no more than six have ever been produced with that title ; besides which we have one book, * De Multangulis Numeris,' on polygonal numbers. These books contain a system of reasoning on numbers by the aid of general symbols, and with some use of sym­bols of operation ; so that, though the demonstra­tions are very much conducted in words at length, and arranged so as to remind us of Euclid, there is no question that the work is algebraical: not a treatise on algebra, but an algebraical treatise on the relations of integer numbers, and on the solu­tion of equations of more than one variable in inte­gers. Hence such questions obtained the name of Diophantine, and the modern works on that pecu-culiar branch of numerical analysis which is called the theory of numbers, such as those of Gauss and Legendre, would have been said, a century ago, to be full of Diophantine analysis. As there are many classical students who will not see a copy of Dio­phantus in their lives, it may be desirable to give one simple proposition from that writer in modern words and symbols, annexing the algebraical phrases from the original.

Book i. qu. 30. Having given the sum of two numbers (20) and their product (96), required the numbers. Observe that the square of the half sum should be greater than the product. Let the differ­ence of the numbers be 2s (ssol /3X); then the sum being 20 (/cv) and the half sum 10 (I) the greater number will be s-f-10 (rera^ce ovv 6 ^zlfav sou evos Kai fjid 1) and the less will be 10—s (,uo i Aefyei sou ez/os, which he would often write fj.5 1 /fi sos a). But the product is 96 (f'-s"') which is also 100 — s2 (p* Aefyet Swcfytews ,tuas, or pv fj\ dv a). Hence s='2 (yiverai 6 sos ijlo /3V) &c.

A young algebraist of our day might hardly be inclined to give the name of algebraical notation to the preceding, though he might admit that there was algebraical reasoning. But if he had consulted the Hindu or Mahommedan writers, or Cardan, Tartaglia, Stevinus, and the other European algebra­ists, who preceded Vieta, he would see that he must either give the name to the notation above exem­plified, or refuse it to everything which preceded the seventeenth century. Diophantus declines his letters, just as we now speak of m th or (m-f-1) th; and {to is an abbreviation of uovds or ilovo&gs, as the case may be.

The question whether Diophantus was an original inventor, or whether he had received a hint from India, the only country we know of which could then have given one, is of great difficulty. We cannot enter into it at length: the veiy great simi-

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