During the late 1930s, Onsager researched the dipole theory of dielectrics. He again improved on earlier work by Peter Debye. However, when he gave his paper to a journal that Debye edited in 1936, it was rejected. Debye would not accept Onsager's ideas until after World War II. During the 1940s, Onsager studied the statistical-mechanical theory of phase transitions in solids. He came up with a mathematical theory which was enthusiastically received. In a tour de force of mathematical physics, he obtained the exact solution for the two dimensional Ising model in zero field in 1944.