Sunday, September 9, 2007

Euclid's Elements

Euclid's Elements

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The frontispiece of Sir Henry Billingsley's first English version of Euclid's Elements, 1570
The frontispiece of Sir Henry Billingsley's first English version of Euclid's Elements, 1570

Euclid's Elements (Greek: Στοιχεῖα) is a mathematical and geometric treatise consisting of 13 books written by the Greek mathematician Euclid in Alexandria circa 300 BC. It comprises a collection of definitions, postulates (axioms), propositions (theorems and constructions), and mathematical proofs of the propositions. The thirteen books cover Euclidean geometry and the ancient Greek version of elementary number theory. With the exception of Autolycus' On the Moving Sphere, the Elements is one of the oldest extant Greek mathematical treatises[1] and it is the oldest extant axiomatic deductive treatment of mathematics.[2] It has proven instrumental in the development of logic and modern science.

Euclid's Elements is the most successful[3][4] and influential[5] textbook ever written. Being first set in type in Venice in 1482, it is one of the very earliest mathematical works to be printed after the invention of the printing press and is second only to the Bible in the number of editions published,[5] with the number reaching well over one thousand.[6] It was used as the basic text on geometry throughout the Western world for about 2,000 years. For centuries, when the quadrivium was included in the curriculum of all university students, knowledge of at least part of Euclid's Elements was required of all students. Not until the 20th century did it cease to be considered something all educated people had read.[7]

Contents

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[edit] History

The frontispiece of Adelard of Bath's Latin translation of Euclid's Elements, c. 1309–1316
The frontispiece of Adelard of Bath's Latin translation of Euclid's Elements, c. 1309–1316

Euclid was a Greek mathematician who wrote Elements in Alexandria during the Hellenistic period (around 300 BC). Scholars believe that the Elements is largely a collection of theorems proved by other mathematicians as well as containing some original work. Proclus, a Greek mathematician who lived several centuries after Euclid, writes in his commentary of the Elements: "Euclid, who put together the Elements, collecting many of Eudoxus's theorems, perfecting many of Theaetetus's, and also bringing to irrefragable demonstration the things which were only somewhat loosely proved by his predecessors".

A version by a pupil of Euclid called Proclo was translated later into Arabic after being obtained by the Arabs from Byzantium and from those secondary translations into Latin. The first printed edition appeared in 1482 (based on Giovanni Campano's 1260 edition), and since then it has been translated into many languages and published in about a thousand different editions. In 1570, John Dee provided a widely respected "Mathematical Preface", along with copious notes and supplementary material, to the first English edition by Henry Billingsley.

Copies of the Greek text also exist, e.g. in the Vatican Library and the Bodleian Library in Oxford. However, the manuscripts available are of very variable quality and invariably incomplete. By careful analysis of the translations and originals, hypotheses have been drawn about the contents of the original text (copies of which are no longer available).

Ancient texts which refer to the Elements itself and to other mathematical theories that were current at the time it was written are also important in this process. Such analyses are conducted by J. L. Heiberg and Sir Thomas Little Heath in their editions of the text.

Also of importance are the scholia, or annotations to the text. These additions, which often distinguished themselves from the main text (depending on the manuscript), gradually accumulated over time as opinions varied upon what was worthy of explanation or elucidation. Some of these are useful and add to the text, but many are not.

[edit] Outline of the Elements

A proof from Euclid's Elements that, given a line segment, an equilateral triangle exists that includes the segment as one of its sides. The proof is by construction: an equilateral triangle ΑΒΓ is made by drawing circles Δ and Ε centered on the points Α and Β, and taking one intersection of the circles as the third vertex of the triangle.
A proof from Euclid's Elements that, given a line segment, an equilateral triangle exists that includes the segment as one of its sides. The proof is by construction: an equilateral triangle ΑΒΓ is made by drawing circles Δ and Ε centered on the points Α and Β, and taking one intersection of the circles as the third vertex of the triangle.

The Elements is still considered a masterpiece in the application of logic to mathematics, and, historically, it has been enormously influential in many areas of science. It is difficult to overstate its influence. Scientists Nicolaus Copernicus, Johannes Kepler, Galileo Galilei, and especially Sir Isaac Newton were all influenced by the Elements, and applied their knowledge of it to their work. Mathematicians (Bertrand Russell, Alfred North Whitehead) and philosophers (e.g., Baruch Spinoza) have also attempted to create their own "Elements", that is, axiomatized deductive structures, as foundations of their own respective disciplines. Even today, introductory mathematics textbooks often have the word elements in their title, e.g. Elements of Information Theory.

The success of the Elements is due primarily to its logical presentation of most of the mathematical knowledge available to Euclid. Much of the material is not original to him, although many of the proofs are his. However, Euclid's systematic development of his subject, from a small set of axioms to deep results, and the consistency of his approach throughout the Elements, encouraged its use as a textbook for about 2,000 years. The Elements still influences modern geometry books. Further, its logical axiomatic approach and rigorous proofs remain the cornerstone of mathematics.

Although Elements is primarily a geometric work, it also includes results that today would be classified as number theory. Euclid probably chose to describe results in number theory in terms of geometry because he couldn't develop a constructible approach to arithmetic. A construction used in any of Euclid's proofs required a proof that it is actually possible. This avoids the problems the Pythagoreans encountered with irrationals, since their fallacious proofs usually required a statement such as "Find the greatest common measure of ..."[8]

[edit] First principles

Euclid's Book 1 begins with 23 definitions — such as point, line, and surface — followed by five postulates and five "common notions" (both of which are today called axioms). These are the foundation of all that follows.

Postulates:

  1. A straight line segment can be drawn by joining any two points.
  2. A straight line segment can be extended indefinitely in a straight line.
  3. Given a straight line segment, a circle can be drawn using the segment as radius and one endpoint as center.
  4. All right angles are congruent.
  5. If two lines are drawn which intersect a third in such a way that the sum of the inner angles on one side is less than two right angles, then the two lines inevitably must intersect each other on that side if extended far enough.

Common notions:

  1. Things which equal the same thing are equal to one another. (Transitive property of equality)
  2. If equals are added to equals, then the sums are equal. (Addition property of equality)
  3. If equals are subtracted from equals, then the remainders are equal. (Subtraction property of equality)
  4. Things which coincide with one another are equal to one another. (Reflexive property of equality)
  5. The whole is greater than the part.

These basic principles reflect the interest of Euclid, along with his contemporary Greek and Hellenistic mathematicians, in constructive geometry. The first three postulates basically describe the constructions one can carry out with a compass and an unmarked straightedge. A marked ruler, used in neusis construction, is forbidden in Euclid construction, probably because Euclid could not prove that verging lines meet.

[edit] Parallel postulate

Main article: Parallel postulate
If the sum of the two interior angles equals 180°, the lines are parallel and will never intersect.
If the sum of the two interior angles equals 180°, the lines are parallel and will never intersect.

The last of Euclid's five postulates warrants special mention. The so-called parallel postulate always seemed less obvious than the others. Euclid himself used it only sparingly throughout the rest of the Elements. Many geometers suspected that it might be provable from the other postulates, but all attempts to do this failed.

By the mid-19th century, it was shown that no such proof exists, because one can construct non-Euclidean geometries where the parallel postulate is false, while the other postulates remain true. For this reason, mathematicians say that the parallel postulate is independent of the other postulates.

Two alternatives to the parallel postulate are possible in non-Euclidean geometries: either an infinite number of parallel lines can be drawn through a point not on a straight line in a hyperbolic geometry (also called Lobachevskian geometry), or none can in an elliptic geometry (also called Riemannian geometry). That other geometries could be logically consistent was one of the most important discoveries in mathematics, with vast implications for science and philosophy. Indeed, Albert Einstein's theory of general relativity shows that the real space in which we live is non-Euclidean.

[edit] Contents of the books

A fragment of Euclid's elements found at Oxyrhynchus, which is dated to circa 100 AD. The diagram accompanies Proposition 5 of Book II of the Elements.
A fragment of Euclid's elements found at Oxyrhynchus, which is dated to circa 100 AD. The diagram accompanies Proposition 5 of Book II of the Elements.

Books 1 through 4 deal with plane geometry:

  • Book 1 contains the basic propositions of geometry: the Pythagorean theorem, equality of angles and areas, parallelism, the sum of the angles in a triangle, and the three cases in which triangles are "equal" (have the same area).
  • Book 2 is commonly called the "book of geometrical algebra," because the material it contains may easily be interpreted in terms of algebra.
  • Book 3 deals with circles and their properties: inscribed angles, tangents, the power of a point.
  • Book 4 is concerned with inscribing and circumscribing triangles and regular polygons.

Books 5 through 10 introduce ratios and proportions:

Books 11 through 13 deal with spatial geometry:

[edit] Criticism

Despite its universal acceptance and success, the Elements has been the subject of substantial criticism. Euclid's parallel postulate, treated above, has been a primary target of critics.[citation needed]

Other criticisms abound. For example, the definitions are not sufficient to describe fully the terms that are defined. In the first construction of Book 1, Euclid used a premise that was neither postulated nor proved: that two circles with centers at the distance of their radius will intersect in two points. Later, in the fourth construction, he used the movement of triangles to prove that if two sides and their angles are equal, then they are congruent; however, he did not postulate or even define movement.

In the 19th century, non-Euclidean geometries attracted the attention of contemporary mathematicians. Leading mathematicians, including Richard Dedekind and David Hilbert, attempted to reformulate the axioms of the Elements, such as by adding an axiom of continuity and an axiom of congruence, to make Euclidean geometry more complete.

Mathematician and historian W. W. Rouse Ball put the criticisms in perspective, remarking that "the fact that for two thousand years [the Elements] was the usual text-book on the subject raises a strong presumption that it is not unsuitable for that purpose."[9]


[edit] Apocrypha

It was not uncommon in ancient time to attribute to celebrated authors works that were not written by them. It is by these means that the apocryphal books XIV and XV of the Elements were sometimes included in the collection.[10] The spurious Book XIV was likely written Hypsicles on a basis of a treatise by Apollonius. The book continues Euclid's comparison of regular solids inscribed in spheres, with the chief result being that the ratio of the surfaces of the dodecahedron and icosahedron inscribed in the same sphere is the same as the ratio of their volumes, the ratio being \sqrt{\tfrac{10}{3(5-\sqrt{5})}}. The spurious Book XV was likely written, at least in part, by Isidore of Miletus. This inferior book covers topics such as counting the number of edges and solid angles in the regular solids, and finding the measure of dihedral angles of faces that meet at an edge.[10]

[edit] Editions

[edit] Translations

[edit] Currently in print

"Euclid's Elements - All thirteen books in one volume" Green Lion Press. ISBN 1-888009-18-7 Based on Heath's translation. www.greenlion.com

[edit] Notes

  1. ^ Boyer (1991). "Euclid of Alexandria", , 101. “With the exception of the Sphere of Autolycus, surviving work by Euclid are the oldest Greek mathematical treatises extant; yet of what Euclid wrote more than half has been lost,”
  2. ^ Ball (1960).
  3. ^ Encyclopedia of Ancient Greece (2006) by Nigel Guy Wilson, page 278. Published by Routledge Taylor and Francis Group. Quote:"Euclid's Elements subsequently became the basis of all mathematical education, not only in the Romand and Byzantine periods, but right down to the mid-20th century, and it could be argued that it is the most successful textbook ever written."
  4. ^ Boyer (1991). "Euclid of Alexandria", , 100. “As teachers at the school he called a band of leading scholars, among whom was the author of the most fabulously successful mathematics textbook ever written - the Elements (Stoichia) of Euclid.”
  5. ^ a b Boyer (1991). "Euclid of Alexandria", , 119. “The Elements of Euclid not only was the earliest major Greek mathematical work to come down to us, but also the most influential textbook of all times. [...]The first printed versions of the Elements appeared at Venice in 1482, one of the very earliest of mathematical books to be set in type; it has been estimated that since then at least a thousand editions have been published. Perhaps no book other than the Bible can boast so many editions, and certainly no mathematical work has had an influence comparable with that of Euclid's Elements.”
  6. ^ The Historical Roots of Elementary Mathematics by Lucas Nicolaas Hendrik Bunt, Phillip S. Jones, Jack D. Bedient (1988), page 142. Dover publications. Quote:"the Elements became known to Western Europe via the Arabs and the Moors. There the Elements became the foundation of mathematical education. More than 1000 editions of the Elements are known. In all probability it is, next to the Bible, the most widely spread book in the civilization of the Western world."
  7. ^ Ball (1960).
  8. ^ Daniel Shanks (2002). Solved and Unsolved Problems in Number Theory. American Mathematical Society.
  9. ^ Ball (1960) p. 55.
  10. ^ a b Boyer (1991). "Euclid of Alexandria", , 118-119. “In ancient times it was not uncommon to attribute to a celebrated author works that were not by him; thus, some versions of Euclid's Elements include a fourteenth and even a fifteenth book, both shown by later scholars to be apocryphal. The so-called Book XIV continues Euclid's comparison of the regular solids inscribed in a sphere, the chief results being that the ratio of the surfaces of the dodecahedron and icosahedron inscribed in the same sphere is the same as the ratio of their volumes, the ratio being that of the edge of the cube to the edge of the icosahedron, that is, \sqrt{10/[3(5-\sqrt{5}}. It is thought that this book may have been composed by Hypsicles on the basis of a treatise (now lost) by Apollonius comparing the dodecahedron and icosahedron. [...] The spurious Book XV, which is inferior, is thought to have been (at least in part) the work of Isidore of Miletus (fl. ca. A.D. 532), architect of the cathedral of Holy Wisdom (Hagia Sophia) at Constantinople. This book also deals with the regular solids, counting the number o edges and solid angles in the solids, and finding the measures of the dihedral angles of faces meeting at an edge.”

[edit] References

  • Ball, W.W. Rouse (1960). A Short Account of the History of Mathematics, 4th ed. [Reprint. Original publication: London: Macmillan & Co., 1908], New York: Dover Publications, pp. 50–62. ISBN 0-486-20630-0.
  • Heath, Thomas L. (1956). The Thirteen Books of Euclid's Elements (3 vols.), 2nd ed. [Facsimile. Original publication: Cambridge University Press, 1925], New York: Dover Publications. ISBN 0-486-60088-2 (vol. 1), ISBN 0-486-60089-0 (vol. 2), ISBN 0-486-60090-4 (vol. 3). Heath's authoritative translation plus his extensive historical research and detailed commentary throughout the text.
  • Boyer, Carl B. (1991). A History of Mathematics, Second Edition, John Wiley & Sons, Inc.. ISBN 0471543977.

[edit] External links

Complete and fragmentary manuscripts of versions of Euclid's Elements :

Retrieved from "http://en.wikipedia.org/wiki/Euclid%27s_Elements"
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