Book excerpt: 9. Nonequivalence of gravitation and acceleration. 9.1. The uniformly rotating disc in Einstein's development of general relativity. 9.2. The Sagnac effect. 9.3. Generalizations of the Sagnac effect. 9.4. The principle of equivalence. 9.5. Fermat's principle of least time and hyperbolic geometry. The rotating disc. 9.7. The FitzGerald-Lorentz contraction via the triangle defect. 9.8. Hyperbolic nature of the electromagnetic field and the Poincare stress. 9.9. The Terrell-Weinstein effect and the angle of parallelism. 9.10. Hyperbolic geometries with non-constant curvature. 9.11. Cosmological models -- 10. Aberration and radiation pressure in the Klein and Poincare models. 10.1. Angular defect and its relation to aberration and Thomas precession. 10.2. From the Klein to the Poincare model. 10.3. Aberration versus radiation pressure on a moving mirror. 10.4. Electromagnetic radiation pressure. 10.5. Angle of parallelism and the vanishing of the radiation pressure. 10.6. Transverse Doppler shifts as experimental evidence for the angle of parallelism -- 11. The inertia of polarization. 11.1. Polarization and relativity. 11.2. Stokes parameters and their physical interpretations. 11.3. Poincare's representation and spherical geometry. 11.4. Polarization of mass. 11.5. Mass in Maxwell's theory and beyond. 11.6. Relativistic stokes parameters