1. G. Candela, Nat. Bur. Std., Washington, D.C., private communication.
2. F. L. Carter, U.S. Naval Research Lab., Washington, D.C., private communication.
3. Observation of electron hopping in 151Eu3S4 by Mössbauer spectroscopy
4. The Theory of Electrical and Magnetic Susceptibilities;Van Vleck,1932