| Chapter I. The Attempts to prove Euclid's Parallel Postulate. |
| 1-5. The Greek Geometers and the Parallel Postulate |
| 6. The Arabs and the Parallel Postulate |
| 7-10. The Parallel Postulate during the Renaissance and the 17th Century |
| Chapter II. The Forerunners on Non-Euclidean Geometry. |
| 11-17. GEROLAMO SACCHERI (1667-1733) |
| 18-22. JOHANN HEINRICH LAMBERT (1728-1777) |
| 23-26. The French Geometers towards the End of the 18th Century |
| 27-28. ADRIEN MARIE LEGENDRE (1752-1833) |
| 29. WOLFGANG BOLYAI (1775-1856) |
| 30. FRIEDRICH LUDWIG WACHTER (1792-1817) |
| 30. (bis) BERNHARD FRIEDRICH THIBAUT (1776-1832) |
| Chapter III. The Founders of Non-Euclidean Geometry. |
| 31-34. KARL FRIEDRICH GAUSS (1777-1855) |
| 35. FERDINAND KARL SCHWEIKART (1780-1859) |
| 36-38. FRANZ ADOLF TAURINUS (1794-1874) |
| Chapter IV. The Founders of Non-Euclidean Geometry (Cont.). |
| 39-45. NICOLAI IVANOVITSCH LOBATSCHEWSKY (1793-1856) |
| 46-55. JOHANN BOLYAI (1802-1860) |
| 56-58. The Absolute Trigonometry |
| 59. Hypotheses equivalent to Euclid's Postulate |
| 60-65. The Spread of Non-Euclidean Geometry |
| Chapter V. The Later Development of Non-Euclidean Geometry. |
| 66. Introduction |
| Differential Geometry and Non-Euclidean Geometry |
| 67-69. Geometry upon a Surface |
| 70-76. Principles of Plane Geometry on the Ideas of RIEMANN |
| 77. Principles of RIEMANN'S Solid Geometry |
| 78. The Work of HELMHOLTZ and the Investigations of LIE |
| Projective Geometry and Non-Euclidean Geometry |
| 79-83. Subordination of Metrical Geometry to Projective Geometry |
| 84-91. Representation of the Geometry of LOBATSCHEWSKY-BOLYAI on the Euclidean Plane |
| 92. Representation of RIEMANN'S Elliptic Geometry in Euclidean Space |
| 93. Foundation of Geometry upon Descriptive Properties |
| 94. The Impossibility of proving Euclid's Postulate |
| Appendix I. The Fundamental Principles of Statistics and Euclid's Postulate. |
| 1-3. On the Principle of the Lever |
| 4-8. On the Composition of Forces acting at a Point |
| 9-10. Non-Euclidean Statics |
| 11-12. Deduction of Plane Trigonometry from Statics |
| Appendix II. CLIFFORD'S Parallels and Surface. Sketch of CLIFFFORD-KLEIN'S Problems. |
| 1-4. CLIFFORD'S Parallels |
| 5-8. CLIFFORD'S Surface |
| 9-11. Sketch of CLIFFORD-KLEIN'S Problem |
| Appendix III. The Non-Euclidean Parallel Construction and other Allied Constructions. |
| 1-3. The Non-Euclidean Parallel Construction |
| 4. Construction of the Common Perpendicular to two non-intersecting Straight Lines |
| 5. Construction of the Common Parallel to the Straight Lines which bound an Angle |
| 6. Construction of the Straight Line which is perpendicular to one of the lines bounding an acute Angle and Parallel to the other |
| 7. The Absolute and the Parallel Construction |
| Appendix IV. The Independence of Projective Geometry from Euclid's Postu |
| 1. Statement of the Problem |
| 2. Improper Points and the Complete Projective Plane |
| 3. The Complete Projective Line |
| 4. Combination of Elements |
| 5. Improper Lines |
| 6. Complete Projective Space |
| 7. Indirect Proof of the Independence of Projective Geometry from the Fifth Postulate |
| 8. BELTRAMI'S Direct Proof of this Independence |
| Appendix V. The Impossibility of proving Euclid's Postulate. An Elementary Demonstration of this Impossibility founded upon the Properties of the System of Circles orthogonal to a Fixed Circle. |
| 1. Introduction |
| 2-7. The System of Circles passing through a Fixed Point |
| 8-12. The System of Circles orthogonal to a Fixed Circle |
| Index of Authors |
| The Science of Absolute Space and the Theory of Parallels |