This lecture covers the analysis of torsion in circular sections, using displacement approaches to find analytical solutions, eigenvalues, and maximum normal stresses. It also delves into the concept of forming an ellipse under rupture conditions and the principle of Saint-Venant, which states that stresses diminish with distance. Additionally, the instructor discusses the application of the principle of superposition in solving engineering problems and the uniqueness theorem of Kirchhoff. The lecture concludes with a discussion on the Saint-Venant principle and its practical applications in engineering.