The following is a paper by H. Aspden published in Lettere al Nuovo Cimento, 25, pp. 456-458 (1979).
Abstract: It is shown that the electric interaction between two charges involves a mutual field energy which, as viewed from either charge, has a field energy distribution that sums to zero over a range equal to the charge separation distance, beyond which it diminishes progressively from a maximum value as the inverse square of distance.
Commentary: Although the author had, long before 1979, established the connection between the law of gravitation and the law of electrodynamics, there remained the elusive mystery of deriving the Neumann potential by a causal argument which did not rely on empirical data. The Neumann potential is an expression for the primary energy action underlying the law of electrodynamics. Somehow energy distributed in a field system set up by two interacting electric charges can find a way of setting up a dynamic potential when the charges are in motion. This means that the energy in the field is being redeployed. It is a start to our understanding of the nature of the action if we know where that energy might be in that field.
The subject paper is one of a series of three devoted to the Coulomb interaction, the electrodynamic interaction [1980a] and the gravitational interaction [1980a], respectively. The Neumann potential proved elusive for several years, but, finally, it did succumb to the author's investigations [1988a, 1995a]. It plays a key role in unifying the force of gravity with electrodynamic law, as is evident from the discussion of 'time dilation' in reference [1996a].