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 Maner Corrected. By Robert Simson, M.D. Emeritus Professor of Mathematics in the University of Glasgow. To this Seventh Edition are Also Annexed Elements of Plain and Spherical Trigonometry