2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/132506The partition function for two-dimensional nearest neighbour Ising models in the presence of a magnetic field is derived . A comparison with the partition functions predicted by Onsager is carried out. The critical temperature estimated by two different methods yields good agreement with the result of Yang and Lee.4 pages;one Figure; References added to the earlier versionChemical Physicstext