A Geometrical Description of the "Classical" Weak-Field Hall Effect in   Metals
  Within the ``anisotropic relaxation time'' approach to transport processes, I obtain a new geometric formula for the weak-field Hall conductivity of metals, which generalizes previously-known formulas due to Tsuji (restricted to cubic 3D metals) and Ong (for 2D metals). 
F. D. M. Haldane