The elements of Euclid viz. 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, And some of Euclid's Demonstrations are restored. Also the book of Euclid's Data, in like manner corrected. By Robert Simson, M. D. Emeritus Professor of Mathematics in the University of Glasgow. To this sixth edition are also annexed, Elements of plain and spherical trigonometry