Starting from a modified Kobayashi-McMillan hamiltonian, (1) phase diagrams of liquid crystals of long molecules are calculated in the mean field approximation; (2) orientation correlation functions are calculated; (3) magnetic birefringence experimental results (of Muta et al.) on homologous series are analysed and explained qualitatively for the first time; (4) apparent exponent △ is calculated and △ = 1.40 is obtained; (5) a new explanation of the even-odd effect of liquid crystals differing from that of Marcelja is proposed. The even-odd effect of supercooling temperature T* is calculated for the first time.