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Contents: CHAPTER I.EUCLID AND THE TRADITIONS ABOUT HIM.CHAPTER II.EUCLID'S OTHER WORKS.CHAPTER III.GREEK COMMENTATORS ON THE ELEMENTS OTHER THAN PROCLUS.CHAPTER IV.PROCLUS AND HIS SOURCES.CHAPTER V.THE TEXT.CHAPTER VI.THE SCHOLIA.CHAPTER VII.EUCLID IN ARABIA.CHAPTER VIII.PRINCIPAL TRANSLATIONS AND EDITIONS OF THE ELEMENTS.CHAPTER IX.BOOK I.BOOK II.Book 3BOOK III.BOOK IV.BOOK V.BOOK VI.BOOK VII.BOOK VIII.BOOK IX.Book 10BOOK X.BOOK XI.BOOK XII.HISTORICAL NOTE.BOOK XIII.HISTORICAL NOTE. 
Euclid, Elements (ed. Thomas L. Heath)
Editions and translations: Greek (ed. J. L. Heiberg)  English (ed. Thomas L. Heath)
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Volume 1 [p. 1] CHAPTER I.EUCLID AND THE TRADITIONS ABOUT HIM.
As in the case of the other great mathematicians of Greece, so in Euclid's case, we have only the most meagre particulars of the life and personality of the man.
Most of what we have is contained in the passage of Proclus' summary relating to him, which is as follows^{1} :
“Not much younger than these (sc. Hermotimus of Colophon and Philippus of Medma) is Euclid, who put together the Elements, collecting many of Eudoxus' theorems, perfecting many of Theaetetus',
and also bringing to irrefragable demonstration the things which were
only somewhat loosely proved by his predecessors. This man lived^{2} in the time of the first Ptolemy. For Archimedes, who came immediately after the first (Ptolemy)^{3} , makes mention of Euclid: and, further, they say that Ptolemy
once asked him if there was in geometry any shorter way than that of
the elements, and he answered that there was no royal road to geometry^{4} . He is then younger than the pupils of Plato but older than Eratosthenes and Archimedes; for the latter were contemporary with one another, as Eratosthenes somewhere says.”
This passage shows that even Proclus had no direct knowledge of Euclid's birthplace or of the date of his birth or death. He proceeds by inference. Since Archimedes lived just after the first [p. 2] Ptolemy, and Archimedes mentions Euclid, while there is an anecdote about some Ptolemy and Euclid, therefore Euclid lived in the time of the first Ptolemy.
We may infer then from Proclus that Euclid was intermediate between the first pupils of Plato and Archimedes. Now Plato died in 347/6, Archimedes lived 287212, Eratosthenes c. 284204 B.C. Thus Euclid must have flourished c. 300 B.C., which date agrees well with the fact that Ptolemy reigned from 306 to 283 B.C.
It is most probable that Euclid received his mathematical training in Athens from the pupils of Plato; for most of the geometers who could have taught him were of that school, and it was in Athens that the older writers of elements, and the other mathematicians on whose works Euclid's Elements depend, had lived and taught. He may himself have been a Platonist, but this does not follow from the statements of Proclus on the subject. Proclus says namely that he was of the school of Plato and in close touch with that philosophy^{5} . But this was only an attempt of a New Platonist to connect Euclid
with his philosophy, as is clear from the next words in the same
sentence, “for which reason also he set before himself, as the end of
the whole Elements, the construction of the socalled Platonic
figures.” It is evident that it was only an idea of Proclus' own to infer that Euclid was a Platonist because his Elements
end with the investigation of the five regular solids, since a later
passage shows him hard put to it to reconcile the view that the
construction of the five regular solids was the end and aim of the Elements
with the obvious fact that they were intended to supply a foundation
for the study of geometry in general, “to make perfect the
understanding of the learner in regard to the whole of geometry^{6} .” To get out of the difficulty he says^{7} that, if one should ask him what was the aim (skopos)
of the treatise, he would reply by making a distinction between
Euclid's intentions (1) as regards the subjects with which his
investigations are concerned, (2) as regards the learner, and would say
as regards (1) that “the whole of the geometer's argument is concerned
with the cosmic figures.” This latter statement is obviously incorrect.
It is true that Euclid's Elements end with the construction of
the five regular solids; but the planimetrical portion has no direct
relation to them, and the arithmetical no relation at all; the
propositions about them are merely the conclusion of the stereometrical
division of the work.
One thing is however certain, namely that Euclid taught, and founded a school, at Alexandria. This is clear from the remark of Pappus about Apollonius^{8} : “he spent a very long time with the pupils of Euclid at Alexandria, and it was thus that he acquired such a scientific habit of thought.”
It is in the same passage that Pappus makes a remark which might, to an unwary reader, seem to throw some light on the [p. 3] personality of Euclid. He is speaking about Apollonius' preface to the first book of his Conics, where he says that Euclid
had not completely worked out the synthesis of the “three and
fourline locus,” which in fact was not possible without some theorems
first discovered by himself. Pappus says on this^{9} : “Now Euclid regarding Aristaeus
as deserving credit for the discoveries he had already made in conics,
and without anticipating him or wishing to construct anew the same
system (such was his scrupulous fairness and his exemplary kindliness
towards all who could advance mathematical science to however small an
extent), being moreover in no wise contentious and, though exact, yet
no braggart like the other [Apollonius] wrote so much about the locus as was possible by means of the conics of Aristaeus,
without claiming completeness for his demonstrations.” It is however
evident, when the passage is examined in its context, that Pappus is not following any tradition in giving this account of Euclid: he was offended by the terms of Apollonius' reference to Euclid, which seemed to him unjust, and he drew a fancy picture of Euclid in order to show Apollonius in a relatively unfavourable light.
Another story is told of Euclid which one would like to believe true. According to Stobaeus^{10} , “some one who had begun to read geometry with Euclid, when he had learnt the first theorem, asked Euclid, ‘But what shall I get bylearning these things?’ Euclid called his slave and said ‘Give him threepence, since he must make gain out of what he learns.’”
In the middle ages most translators and editors spoke of Euclid as Euclid of Megara. This description arose out of a confusion between our Euclid and the philosopher Euclid of Megara who lived about 400 B.C. The first trace of this confusion appears in Valerius Maximus (in the time of Tiberius) who says^{11} that Plato, on being appealed to for a solution of the problem of doubling the cubical altar, sent the inquirers to “Euclid the geometer.” There is no doubt about the reading, although an early commentator on Valerius Maximus wanted to correct “Eucliden” into “Eudoxum,” and this correction is clearly right. But, if Valerius Maximus took Euclid the geometer for a contemporary of Plato, it could only be through confusing him with Euclid of Megara. The first specific reference to Euclid as Euclid of Megara belongs to the 14th century, occurring in the hupomnêmatismoi of Theodorus Metochita (d. 1332) who speaks of “Euclid of Megara, the Socratic philosopher, contemporary of Plato,” as the author of treatises on plane and solid geometry, data, optics etc. : and a Paris
MS. of the 14th century has “Euclidis philosophi Socratici liber
elementorum.” The misunderstanding was general in the period from
Campanus' translation (Venice 1482) to those of Tartaglia (Venice 1565) and Candalla (Paris 1566). But one Constantinus Lascaris (d. about 1493) had already made the proper [p. 4] distinction by saying of our Euclid that “he was different from him of Megara of whom Laertius wrote, and who wrote dialogues”^{12} ; and to Commandinus belongs the credit of being the first translator^{13}
to put the matter beyond doubt: “Let us then free a number of people
from the error by which they have been induced to believe that our Euclid is the same as the philosopher of Megara” etc.
Another idea, that Euclid was born at Gela in Sicily, is due to the same confusion, being based on Diogenes Laertius' description^{14} of the philosopher Euclid as being “of Megara, or, according to some, of Gela, as Alexander says in the Diadochai.”
In view of the poverty of Greek tradition on the subject even as early as the time of Proclus (410485 A.D.), we must necessarily take cum grano the apparently circumstantial accounts of Euclid
given by Arabian authors; and indeed the origin of their stories can be
explained as the result (1) of the Arabian tendency to romance, and (2)
of misunderstandings.
We read^{15} that “Euclid, son of Naucrates, grandson of Zenarchus^{16} , called the author of geometry, a philosopher of somewhat ancient date, a Greek by nationality domiciled at Damascus, born at Tyre,
most learned in the science of geometry, published a most excellent and
most useful work entitled the foundation or elements of geometry, a
subject in which no more general treatise existed before among the Greeks: nay, there was no one even of later date who did not walk in his footsteps and frankly profess his doctrine. Hence also Greek, Roman
and Arabian geometers not a few, who undertook the task of illustrating
this work, published commentaries, scholia, and notes upon it, and made
an abridgment of the work itself. For this reason the Greek
philosophers used to post up on the doors of their schools the
wellknown notice: ‘Let no one come to our school, who has not first
learned the elements of Euclid.’” The details at the beginning of this extract cannot be derived from Greek sources, for even Proclus did not know anything about Euclid's father, while it was not the Greek habit to record the names of grandfathers, as the Arabians commonly did. Damascus and Tyre were no doubt brought in to gratify a desire which the Arabians always showed to connect famous Greeks in some way or other with the East. Thus Nas<*>īraddīn, the translator of the Elements, who was of T<*>ūs in Khurāsān, actually makes Euclid out to have been “Thusinus” also^{17} . The readiness of the Arabians to run away with an idea is illustrated by the last words [p. 5]
of the extract. Everyone knows the story of Plato's inscription over
the porch of the Academy: “let no one unversed in geometry enter my
doors”; the Arab turned geometry into Euclid's geometry, and told the story of Greek philosophers in general and “their Academies.”
Equally remarkable are the Arabian accounts of the relation of Euclid and Apollonius^{18} . According to them the Elements were originally written, not by Euclid, but by a man whose name was Apollonius, a carpenter, who wrote the work in 15 books or sections^{19} . In the course of time some of the work was lost and the rest became disarranged, so that one of the kings at Alexandria
who desired to study geometry and to master this treatise in particular
first questioned about it certain learned men who visited him and then
sent for Euclid who was at that time famous as a geometer, and asked him to revise and complete the work and reduce it to order. Euclid then rewrote it in 13 books which were thereafter known by his name. (According to another version Euclid composed the 13 books out of commentaries which he had published on two books of Apollonius
on conics and out of introductory matter added to the doctrine of the
five regular solids.) To the thirteen books were added two more books,
the work of others (though some attribute these also to Euclid) which contain several things not mentioned by Apollonius. According to another version Hypsicles, a pupil of Euclid at Alexandria, offered to the king and published Books XIV. and XV., it being also stated that Hypsicles had “discovered” the books, by which it appears to be suggested that Hypsicles had edited them from materials left by Euclid.
We observe here the correct statement that Books XIV. and XV. were not written by Euclid, but along with it the incorrect information that Hypsicles, the author of Book XIV., wrote Book XV. also.
The whole of the fable about Apollonius having preceded Euclid and having written the Elements appears to have been evolved out of the preface to Book XIV. by Hypsicles, and in this way; the Book must in early times have been attributed to Euclid, and the inference based upon this assumption was left uncorrected afterwards when it was recognised that Hypsicles was the author. The preface is worth quoting:
“Basilides of Tyre, O Protarchus, when he came to Alexandria
and met my father, spent the greater part of his sojourn with him on
account of their common interest in mathematics. And once, when [p. 6] examining the treatise written by Apollonius
about the comparison between the dodecahedron and the icosahedron
inscribed in the same sphere, (showing) what ratio they have to one
another, they thought that Apollonius
had not expounded this matter properly, and accordingly they emended
the exposition, as I was able to learn from my father. And I myself,
later, fell in with another book published by Apollonius,
containing a demonstration relating to the subject, and I was greatly
interested in the investigation of the problem. The book published by Apollonius
is accessible to all for it has a large circulation, having
apparently been carefully written out laterbut I decided to send you
the comments which seem to me to be necessary, for you will through
your proficiency in mathematics in general and in geometry in
particular form an expert judgment on what I am about to say, and you
will lend a kindly ear to my disquisition for the sake of your
friendship to my father and your goodwill to me.”
The idea that Apollonius preceded Euclid must evidently have been derived from the passage just quoted. It explains other things besides. Basilides must have been confused with basileus, and we have a probable explanation of the “Alexandrian king,” and of the “learned men who visited” Alexandria. It is possible also that in the “Tyrian” of Hypsicles' preface we have the origin of the notion that Euclid was born in Tyre. These inferences argue, no doubt, very defective knowledge of Greek: but we could expect no better from those who took the Organon of Aristotle to be “instrumentum musicum pneumaticum,” and who explained the name of Euclid, which they variously pronounced as Uclides or Icludes, to be compounded of Ucli a key, and Dis a measure, or, as some say, geometry, so that Uclides is equivalent to the key of geometry!
Lastly the alternative version, given in brackets above, which says that Euclid made the Elements out of commentaries which he wrote on two books of Apollonius
on conics and prolegomena added to the doctrine of the five solids,
seems to have arisen, through a like confusion, out of a later passage^{20} in Hypsicles' Book XIV.: “And this is expounded by Aristaeus in the book entitled ‘Comparison of the five figures,’ and by Apollonius
in the second edition of his comparison of the dodecahedron with the
icosahedron.” The “doctrine of the five solids” in the Arabic must be
the “Comparison of the five figures” in the passage of Hypsicles, for nowhere else have we any information about a work bearing this title, nor can the Arabians have had. The reference to the two books of Apollonius on conics will then be the result of mixing up the fact that Apollonius wrote a book on conics with the second edition of the other work mentioned by Hypsicles. We do not find elsewhere in Arabian authors any mention of a commentary by Euclid on Apollonius and Aristaeus: so that the story in the passage quoted is really no more than a variation of the fable that the Elements were the work of Apollonius.
^{1} Proclus, ed. Friedlein, p. 68, 620. ^{2} The word gegone must apparently mean “flourished,” as Heiberg understands it (Litterargeschichtliche Studien über Euklid, 1882, p. 26), not “was born,” as Hankel took it : otherwise part of Proclus' argument would lose its cogency. ^{3} So Heiberg understands epibalôn tôi prôtôi (sc. Ptolemaiôi). Friedlein's text has kai between epibalôn and tôi prôtôi; and it is right to remark that another reading is kai en tôi prôtôi (without epibalôn) which has been translated “in his first book,” by which is understood On the Sphere and Cylinder I., where (1) in Prop. 2 are the words “let BC be made equal to D by the second (proposition) of the first of Euclid's (books),” and (2) in Prop. 6 the words “For these things are handed down in the Elements” (without the name of Euclid). Heiberg thinks the former passage is referred to, and that Proclus must therefore have had before him the words “by the second of the first of Euclid”: a fair proof that they are genuine, though in themselves they would be somewhat suspicious. ^{4} The same story is told in Stobaeus, Ecl. (II. p. 228, 30, ed. Wachsmuth) about Alexander and Menaechmus. Alexander is represented as having asked Menaechmus
to teach him geometry concisely, but he replied : “O king, through the
country there are royal roads and roads for common citizens, but in
geometry there is one road for all.” ^{5} Proclus, p. 68, 20, kai têi proairesei de Platônikos esti kai têi philosophiai tautêi oikeios. ^{6} ibid. p. 71, 8. ^{7} ibid. p. 70, 19 sqq. ^{8} Pappus, VII. p. 678, 1012, suscholasas tois hupo Eukleidou mathêtais en Alexandrei<*> pleiston chronon, hothen esche kai tên toiautên exin ouk amathê. ^{9} Pappus,
VII. pp. 676, 25678, 6. Hultsch, it is true, brackets the whole
passage pp. 676, 25678, 15, but apparently on the ground of the
diction only. ^{10} Stobaeus, l.c. ^{11} VIII. 12, ext. 1. ^{12} Letter to Fernandus Acuna, printed in Maurolycus, Historia Siciliae, fol. 21 r. (see Heiberg, EuklidStudien, pp. 223, 25). ^{13} Preface to translation (Pisauri, 1572). ^{14} Diog. L. II. 106, p. 58 ed. Cobet. ^{15} Casiri, Bibliotheca ArabicoHispana Escurialensis, I. p. 339. Casiri's source is alQifti (d. 1248), the author of the Ta'rīkh alH<*>ukamā, a collection of biographies of philosophers, mathematicians, astronomers etc. ^{16} The Fihrist says “son of Naucrates, the son of Berenice (?)” (see Suter's translation in Abhandlungen zur Gesch. d. Math. VI. Heft, 1892, p. 16). ^{17} The same predilection made the Arabs describe Pythagoras as a pupil of the wise Salomo, Hipparchus as the exponent of Chaldaean philosophy or as the Chaldaean, Archimedes as an Egyptian etc. (H<*>ăjī Khalfa, Lexicon Bibliographicum, and Casiri). ^{18} The authorities for these statements quoted by Casiri and H<*>ājī Khalfa are alKindi's tract de instituto libri Euclidis (alKindī died about 873) and a commentary by Qād<*>īzāde arRūmī (d. about 1440) on a book called Ashkāl atta' sīs (fundamental propositions) by Ashraf Shamsaddīn asSamarqandī (c. 1276) consisting of elucidations of 35 propositions selected from the first books of Euclid. Nas<*>īraddīn likewise says that Euclid
cut out two of 15 books of elements then existing and published the
rest under his own name. According to Qād<*>īzāde the king heard
that there was a celebrated geometer named Euclid at Tyre: Nas<*>īraddīn says that he sent for Euclid of T<*>ūs. ^{19} So says the Fihrist. Suter (op. cit. p. 49) thinks that the author of the Fihrist did not suppose Apollonius of Perga to be the writer of the Elements, as later Arabian authorities did, but that he distinguished another Apollonius whom he calls “a carpenter.” Suter's argument is based on the fact that the Fihrist's article on Apollonius (of Perga) says nothing of the Elements; and that it gives the three great mathematicians, Euclid, Archimedes and Apollonius, in the correct chronological order. ^{20} Heiberg's Euclid, vol. V. p. 6.
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