W. Heisenberg's paper on the theory of ferromagnetism addresses the Weissian molecular forces, which are reinterpreted in quantum mechanical terms. The paper discusses the limitations of the classical theory, particularly the discrepancies between predicted and observed magnetic forces in ferromagnetic materials. Heisenberg introduces a new model inspired by the Uhlenbeck-Goudsmit theory of spin electrons, suggesting that only the magnetic moments of electrons, not the atoms themselves, align in ferromagnetic crystals. This challenges the interpretation of Weissian forces as electric interactions between electrons. The paper also reviews approximation methods used in treating electron motion in metals, emphasizing the importance of Coulomb interactions and Pauli's principle in explaining ferromagnetic phenomena.W. Heisenberg's paper on the theory of ferromagnetism addresses the Weissian molecular forces, which are reinterpreted in quantum mechanical terms. The paper discusses the limitations of the classical theory, particularly the discrepancies between predicted and observed magnetic forces in ferromagnetic materials. Heisenberg introduces a new model inspired by the Uhlenbeck-Goudsmit theory of spin electrons, suggesting that only the magnetic moments of electrons, not the atoms themselves, align in ferromagnetic crystals. This challenges the interpretation of Weissian forces as electric interactions between electrons. The paper also reviews approximation methods used in treating electron motion in metals, emphasizing the importance of Coulomb interactions and Pauli's principle in explaining ferromagnetic phenomena.