THE E L E M E N T S OF EU CL I D, V I 2. THE FIRST SIX BOOKS, TOGETHER WITH THE ELEVENTH AND TWELFTH. The Errors, by which Theon, or others, have long ago vitiated these Books, are corrected, Emeritus Profeffor of Mathematics in the University of Glasgow. to this Nintă Edition are also annexed É D IN BU R G H: PRINTED FOR E. WINGROVE, LONDON, AND J. BALFOUR, EDINBURGH, M, DCC, XCIII. TO THE K I N G ; THIS EDITION OF THI PRINCIPAL BOOKS OF THE ELEMENTS OF EUCLID, AND OF THE BOOK OF HIS DATA, IS MOST NUM B L Y DEDICATED, BY HIS MAJESTY's MOST DUTIFUL, AND MOST DEVOTED SUBJECT AND SERVANT, ROBERT SIMSON. HE Opinions of the Moderns concerning the Author of the Elements of Geometry, which go under Euclid's name, are very different and contrary to one another. Peter Ramus ascribes the Propofitions, as well as their Demonstrations, to Theon ; others think the Propositions to be Euclid's, but that the Demonftrations are Theon's; and others maintain that all the Propositions and their Demonstrations are Euclid's own. John Buteo and Sir Henry Savile are the Authors of greatest Note who affert this last ; and the greater part of Geometers have ever since been of this Opinion, as they thought it the most probable. Sir Henry Savile after, the several Arguments he brings to prove it, makes this Con clufion, (Page 13. Praelect.) "That, excepting a very few Interpolations, Explications, and Additions, Theon altered “ nothing in Euclid.” But, by often considering and comparing together the Definitions and Demonstrations as they are in the Greek Editions we now have, I found that Theon, or whoever was the Editor of the present Greek Text, by adding some things, suppressing others, and mixing his own with Euclid's Demonftrations, had changed more things to the worse than is commonly supposed, and those not of small moment, especially in the Fifth and Eleventh Books of the Elements, which this Editor has greatly yitiated; for instance, by substituting a fhorter, but insufficient Demonstration of the 18th Prop. of the sth Book, in place of the legitimate one which Euclid had given; and by taking out of this Book, besides other things, the good Definition which Eudoxus or Euclid had given of Compound Ratio, and given an absurd one in place of it in the 5th Definition of the 6th Book, which neither Euclid, Archimedes, Appolonius, nor any Geometer before Theon's time, ever made, use of, and of which there is not to be found the least appearance in ot their Writings ; and, as this Definition did much embarrass Beginners, and is quite useless, it is now thrown out of the Elements, and another, which, without doubt, Euclid had given, is put in its proper place among the Def{nitions of the 5th |