  The recent progress in the theory of generalized Lambert functions makes
possible to solve exactly the Weiss equation of ferromagnetism. However, this
solution is quite inconvenient for practical purposes. Precise approximate
analytical solutions are obtained, giving the temperature dependence of the
spontaneous magnetization, and also the dependence of the magnetization on both
temperature and external magnetic field. The experimental relevance of these
results, mainly for the determination of the Curie temperature, is discussed.
