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It is shown how Maxwell's electromagnetic equations in General Relativity may be expressed in the form of a single four-vector density equation, in which the field tensor has only three distinct complex components. The number of equations is reduced, but all the usual classical formulae may be obtained by separating the real and imaginary parts.

Based on the complete set of equations of thermodynamics of irreversible processes of a fluid in electromagnetic fields, a relativistic theory of the influence of electromagnetic waves on a simple fluid is developed. In particular, the oscillations of the fluid induced by a plane electromagnetic wave are evaluated, and the energy‐momentum tensor is determined. It is further conjectured that Minkowski's tensor and Abraham's tensor lead to the same result when matter is properly taken into account. The irreversible processes of heat conduction and viscosity accompanying the oscillations of matter are briefly discussed.

A unified theory of gravitation and electromagnetism is derived from a variational principle. The characteristic action function is an invariant density formed from the Ricci tensor of a semi-symmetric connection. The field equations have the same general character as those of the Born-Infeld electrodynamics and its generalization by Hoffmann and Infeld. The theory presupposes the existence of a fundamental length of the order of magnitude of the electron radius. The Einstein-Maxwell equations are obtained from a special choice of the action function.

The question of the form of the momentum-energy tensor of the electromagnetic field (in a medium) remains debatable to this day. The dilemma of whether the photon momentum in a medium is equal to nhν/c (Minkowski) or hν/nc (Abraham) therefore remains unresolved (n is the refractive index). Simple considerations based on the law governing the motion of the center of gravity of the "field + medium" system lead, however, to a unique choice of Abraham's tensor. The Jones-Richards experiments do not contradict this, although they do not lead to a solution of the problem. In principle, measurements of the Jones-Richards type (of the pressure of light in media) in the pulsed regime would yield the solution of the problem. Considerable space is allotted to an analysis of the question of the "rejection" of Abraham's tensor, a question advanced by Laue and supported by many authors. It is shown that the use of the Laue criterion is based on an error in the very formulation of the question. The arguments advanced in this connection are illustrated by using as an example analogous relations in the case of the motion of a simple static system, namely a charged capacitor. The conservations laws applied to a static electromagnetic field having angular momentum also lead to Abraham's expression for the field momentum density.

It is shown how the general relativistic electromagnetic equations for a material medium can be expressed in the form of a single four-vector density equation. The field tensor has six different complex components instead of three, as in the case of a, free medium. The classical equations are obtained by separating the real and imaginary parts.

TYABJI1 has shown that the energy momentum tensor in the vortical form of Dirac's new electromagnetic theory2 has the same form as that belonging to the non-vortical theory. The method he uses of first obtaining a non-symmetrical form and then adding a suitable symmetrizing term depends on the particular definition of the electromagnetic potential Aµ and thus does not show why the two energy momentum tensors should have the same form.

Maxwell field equations and constitutive equations, discussing best pedagogical formulation for electrodynamics