PREF A CE. In the preparation of the present edition of the Geometry of A. M. LEGENDRE, the original has been consulted as a model and guide, but not implicitly followed as a standard. The language employed, and the arrangement of the arguments in many of the demonstrations, will be found to differ essentially from the original, and also from the English translation by DR. BREWSTER. In the original work, as well as in the translation, the propositions are not enunciated in general terms, but with reference to, and by the aid of, the particular diagrams used for the demonstrations. It is believed that this departure from the method of Euclid has been generally regretted. The propositions of Geometry are general truths, and as such, should be stated in general terms, and without reference to particular figures. The method of enunciating them by the aid of particular diagrams seems to have been adopted to avoid the difficulty which beginners experience in comprehending abstract propositions. But in avoiding this difficulty, and thus lessening, at first, the intellectual labor, the faculty of abstraction, which it is one of the primary objects of the study of Geometry to strengthen, remains, to a certain extent, un improved. The methods of demonstration, in several of the Books, have been entirely changed. By regarding the circle as the limit of the inscribed and circumscribed polygons, the demonstrations in Book V. have been much simplified; and the same principle is made the basis of several important demonstrations in Book VIII. The subjects of Plane and Spherical Trigonometry have been treated in a manner quite different from that employed in the original work. In Plane Trigonometry, especially, important changes have been made. The separation of the part which relates to the computations of the sides and angles of triangles from that which is purely analytical, will, it is hoped, be found to be a decided improvement. The application of Trigonometry to the measurement of Heights and Distances, embracing the use of the Table of Logarithms, and of Logarithmic Sines; and the application of Geometry to the mensuration of planes and solids, are useful exercises for the Student. Practical ex. amples cannot fail to point out the generality and utility of abstract science. FISHKILL LANDING, I July, 1851. To Find from the Table the Logarithm of a Number,.. To Find from the Table the Number corresponding to a Given Loga- Multiplication by Logarithms,... To find the Powers and Roots of Numbers, by Logarithms,. Geometrical Constructions, ----- Description of Instruments,... Diagonal Scale of Equal Parts,... To Lay off an Angle with a Protractor, Plane Trigonometry, Defined,-- Division of the Circumference,.. Definitions of Trigonometrical Lines, Table of Logarithmic Sines,... To Find from the Table, the Logarithmic Sine, &c., of an Arc or Angle, 274 To Find the Degrees, &c., Answering to a Given Logarithmic Sine, &c., 276 Solution of Right-Angled Triangles,.... 321 321 321 329 SᏢᎻ Ꭼ ᎡᏆCA L TᎡᏆ G ONO M EᎢᎡY. Spherical Triangle, Defined, --..... Spherical Trigonometry, Defined ----- Solution of Right-Angled Spherical Triangles, by Logarithms,- Solution of Oblique-Angled Triangles, by Logarithms,............ 351 351 Area, or Contents of a Surface,-------.. Unit of Measure for Surfaces --------- Area of a Square, Rectangle, or Parallelogram,- 347 Area of an Irregular Polygon,... Area of a Long and Irregular Figure bounded on One Side by a Right Area of a Regular Polygon,------ To Find the Circumference or Diameter of a Circle, To find the Length of an Arc,..... Area of a Sector of a Circle,... |