1. Hobson , E. W. 1931 The theory ofspherical and ellipsoidal harmonics , Cambridge University Press, Cambridge
2. MacRobert , T.M. 1947 Spherical Harmonics. An Elementary Treatise on Harmonic Functions with Applications , Methuen & Co. Ltd., London, second edition
3. Morse , P.M. Feshbach , H. 1953 Methods of theoretical physics. 2 volumes , McGraw-Hill Book Co., Inc., New York