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Emeritus Professor of Mathematics in the University of Glasgow.


Printed for J. Nourse, London ; and J. BALFOUR, Edinburgh




P R E F A C E.
UCLID's DATA is the first in order of the

books written by the ancient geometers to facilitate and promote the method of resolution or analysis. In the general, a thing is faid to be given which is either actually exhibited, or can be found out, that is, which is either known by hypothesis, or that can be demonstrated to be known; and the propositions in the book of Euclid's Data shew what things can be found out or known from those that by hypothesis are already known; so that in the analysis or investigation of a problem, from the things that are laid down to be known or given, by the help of these propositions other things are demonstrated to be given, and from these, other things are again shewn to be given, and so on, until that which was proposed to be found out in the problem is demonstrated to be given, and when this is done, the problem is folved, and its composition is made and derived from the compositions of the Data which were made use of in the analysis. And thus the Data of Euclid are of the most general and necessary use in the solution of problems of every kind.

Euclid is reckoned to be the author of the Book of the Data, both by the ancient and modern geometers; and there seems to be no doubt of his having written a book on this subject, but which, in the course of so many ages, has been much vitiated by unskilful editors in several places, both in the order of the propositions, and in the definitions and demonstrations themselves. To cor



rect the errors which are now found in it, and bring it nearer to the accuracy with which it was, no doubt, at first written by Euclid, is the design of this edition, that so it may be rendered more useful to geometers, at least to beginners who defire to learn the investigatory method of the ancients. And for their fakes, the compositions of most of the Data are subjoined to their demonstrations, that the compositions of problems folved by help of the Data may be the more easily made.

Marinus the philosopher's preface, which, in the Greek edition, is prefixed to the data, is here left out, as being of no use to understand them, At the end of it, he says, that Euclid has not ua fed the synthetical, but the analytical method in delivering them; in which he is quite mistaa ken; for in the analysis of a theorem, the thing to be demonstrated is assumed in the analysis; but in the demonstrations of the Data, the thing to be demonstrated, which is, that something or other is given, is never once assumed in the demonstration, from which it is manifest, that every one of them is demonstrated synthetically ; though indeed, if a proposition of the Data be turned into a problem, for example the 84th or 85th in the former editions, which here are the 85th and 86th, the demonstration of the

proposition becomes the analysis of the problem.

Wherein this edition differs from the Greek, and the reasons of the alterations from it, will be thewn in the notes at the end of the Data,


E U C L I D's





PACES, lines, and angles, are said to be given in magnitude, when equals to them can be found.

II. A ratio is said to be given, when a ratio of a given magnitude

to a give magnitude which is the same ratio with it can be found,

III. Rectilineal figures are said to be given in species, which have each of their angles given, and the ratios of their sides given,

IV. Points, lines, and spaces, are said to be given in position, which

have always the same situation, and which are either actually cxhibited, or can be found.


An angle is said to be given in position, which is contained by straight lines given in position.

V. A circle is said to be given in magnitude, when a straight line from its centre to the circumference is given in magnitude.

VI. A circle is said to be given in position and magnitude, the centre

of which is given in position, and a straight line from it to the circumference is given in magnitude.

VII. Segments of circles are faid to be given in magnitude, when the angles in them, and their bases, are given in magnitude.

VIII. Segments of circles are said to be given in position and mag

nitude, when the angles in them are given in magnitude, and their bafes are given both in position and magnitude.

IX. A magnitude is said to be greater than anoth:12 given magnitude, when this given mignitude

from it, the remainder is equal to the other


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