Equivalence of basic clusters and for Approximation of the triangular net and that of and for the square net are explained applying Wataru-Kurata's “paeudo-configuration” method. Equivalence of Bethe's original assumption with Takagi's method is illustrated using g (5) 12 of W-K's paper.
An attempt to treat approximately the Heisenberg model of feromagnetism, or to take into account the exchange coupling in a better way than in the Ising model, is explained for various lattices, generalizing author's treatment of the Ising model reported recently. In the best approximations so far calculated, ferromagnetic states appear only for the three-dimensional lattices, which remain ferromagnetic even near the absolute zero. But difficulties still remain for low tempetatures.