1. A.J. Wallard, Proc.. R.. Inst. 69, 107 (1998)
2. H.W. Miller, 1856, Phil Trans, cxivi
3. G. Giogi, Elettroteen, 5, 402 (1901)
4. Maxewell, A Treatise on Electricity and Magnetism, vol. II, (Oxford Press, Oxford, 1873)
5. D.R. Hartree, Proc. Camb. Philol. Soc. 24, 89 (1926)