1. Pippard, A. B., Proc. Roy. Soc., A, 191, 385 (1947).
2. Wilson, A. H., "The Theory of Metals", 158 (Cambridge, 1936).
3. Titchmarsh, E. C., "Introduction to the Theory of Fourier Integrals", chap. 11 (Oxford, 1937).
4. Pippard, A. B., Proc. Roy. Soc., A, 191, 399 (1947).