Great efforts have been expended on the electron theory of metals during the last thirty years. The classical theory was at fault because it considered the electrons as entirely free. The quantum theory partly remedied this fault. In the first place, through application of the exclusion principle, the interaction between the electrons was schematically taken into account. In the second place the effect of the remaining ion lattice was introduced by placing the electrons into a fixed triply periodic field of force, corresponding to the distribution of the positive metal ions over the lattice. The results of all these efforts are still far from satisfactory. In particular the phenomenon known as superconductivity has so far defied all explanation.