The original data of Weiss and Forrer are reanalyzed with the aim to obtain a precise relation between the observed temperature rise and the magnetic field strength at temperatures both above and below the Curie temperature. The application of nonlinear least squares analysis reveals that a simple dependence of the temperature rise upon the magnetic field strength does not give a good fit. A more complex expression is therefore used, employing two different exponents (as adjustable parameters) for the magnetic field strength. The exponent 2, required in the original theory of Weiss, appears only in the paramagnetic region, while exponent 3 applies in the ferromagnetic region. The second exponent, valid at high fields, is close to 1 in the ferromagnetic region and near 0.7 in the paramagnetic region (lower values are obtained for some temperatures, but are shown to be of low significance).