  The classical Heisenberg model has been solved in spatial d dimensins,
exactly in d=1 and by the Migdal-Kadanoff approximation in d>1, by using a
Fourier-Legendre expansion. The phase transition temperatures, the energy
densities, and the specific heats are calculated in arbitrary dimension d.
Fisher's exact result is recovered in d=1. The absence of an ordered phase,
conventional or algebraic (in contrast to the XY model yielding an
algebraically ordered phase), is recovered in d=2. A conventionally ordered
phase occurs at d>2. This method opens the way to complex-system calculations
with Heisenberg local degrees of freedom.
