Letter to the editors

I thank H. J. Wintle for his letter (IEEE Electr. Insul. Mag., vol. 30, no. 2, pp. 5-6, 2014) stimulated by those of myself and E. Lemke (IEEE Electr. Insul. Mag., vol. 29, no. 5, pp. 6-9, 2013). The discussion and references were interesting, and I am grateful for the corroboration. The suggestion of our being unaware of the Shockley-Ramo theorem, or at least of its implications, is a little surprising; my letter should be read in the context of the two articles by Lemke that it discusses, the first of which mentions the Ramo-Shockley theorem by name and cites Shockley\´s 1938 paper. Pedersen et al. (IEEE Trans. Electr. Insul., vol. 26, pp. 487-497, 1991), also cited in that first article and mentioned by me, give a solution to the relation of space charge and induced charge, and note that "Formulae similar to those derived above, but for systems in which polarizable materials are absent, have been given by many authors, see e.g. von Engel and Steenbeck, Shockley, Ramo. These formulae are sometimes referred to as the Ramo-Shockley theorem. It should be remembered, however, that these formulae were readily available in the standard literature prior to the publication of the papers by Ramo and Shockley, and that a quantitative treatment based on Faraday??s concept of induced charge dates back at least to Maxwell."