1. L. D. Landau and E. Lifshitz, The Classical Theory of Fields, Pergamon, Oxford (1975) (Russian original published by Fizmatgiz (1962)).
2. L. D. Landau and E. Lifshitz, Quantum Mechanics: Nonrelativistic Theory, Pergamon, Oxford (1958) (Russian original published by Nauka (1974)).
3. E. W. Hobson, The Theory of Spherical and Ellipsoidal Harmonics, Cambridge (1931), Ch.4.
4. J. C. Maxwell, A Treatise on Electricity and Magnetism, Vol. 1, Oxford (1892), Ch.9.
5. J. D. Jackson, Classical Electrodynamics, New York (1962).