Superconductivity in transition metals and compounds

A qualitative account of the $T_c$ systematics of transition metals and compounds is presented from a novel point of view. The suggestion is that the $d$ density of states at the Fermi surface is zero near the center of the series. The idea unifies the $T_c$ systematics with other physical properties, and includes the relationship betwen high $T_c$ and lattice instability. The superconductivity of rare earths and neighboring elements is considered with special emphasis on the role of the $4f$ core.