completely filled with a dielectric. The dielectric and outer electrode of the capacitor can rotate about a common axis freely and independently. By considering the conservation of angular momentum Skobel'tsyn again showed that Minkowski's tensor contradicts the conservation laws At the same time as Skobeltsyn, J. P. Gordon [16] wrote a paper demonstrating that Abrahams form is correct for a nondispersive dielectric media, and that Minkowski's form, which deals with"crystal momentum, or "pseudomomentum may be used to compute the radiation pressure on objects embedded in such a dielectric media. Gordons argument followed the line that radiation' pressure was a combination of ponderomotive forces exerted directly by the field in the medium and forces exerted on the medium by the dielectric in the presence of the field In his 1979 paper [17] in response to Walker, Lahoz and Walker's experiment [18 Brevik explained why the Abraham force could not be measured directly and why the divergence-free Minkowski tensor was perfectly satisfactory for explaining all existing torque experiments in optics. He noted that a microscopical energy- momentum tensor can be constructed for a closed system(that is, the field plus matter) and it can be averaged over suitable space-time regions, obtaining terms for pure field or matter plus a number of complicated correlation terms. This means there is no unique way to separate the total energy-momentum tensor into a field part and a matter part To obtain a definite energy-momentum tensor it is possible to impose extra restriction based on physical arguments, such as the Laue and Moller criterions that is, that the propagation velocity of the energy of a light wave in a moving body shall transform like a particle velocity under Lorentz transformations)-and if they are applied, Minkowski's tensor satisfies these criterion while Abrahams does not However, Brevik notes that such criteria are a test of a tensors convenience rather than its correctness Brevik was writing at a time when the problem had come back in fashion, and in the previous few years some important work had been done on it, such as the measuring of the abraham force directly by Walker, Lahoz and Walker [18] Current experimental trends were moving along both microscopical and macroscopical lines. Brevik believed: The microscopical method is advantageous from a fundamental viewpoint, but its drawback is that it easily becomes formally complicated and tends to obscure a simple physical interpretation The advantage of the simple and less fundamental macroscopical method is its close connection with observation At this time Brevik's interest was lying in the consideration of the electrostriction effect(or the magnostriction effect). He stated that although the electrostriction effect does not affect many experiments it does in special cases, so one should bear its existence in mind and add the helmholtz electrostriction term to abrahams or Minkowski's tensor whenever necessary. He reinforces this on page 139 Minkowski s tensor does not describe electrostriction or magnetostriction. This tensor, therefore, is unable to give a complete description of the local electromagnetic state in the medium. However, he then continued that it does not matter 1212 completely filled with a dielectric. The dielectric and outer electrode of the capacitor can rotate about a common axis freely and independently. By considering the conservation of angular momentum Skobel’tsyn again showed that Minkowski’s tensor contradicts the conservation laws. At the same time as Skobel’tsyn, J. P. Gordon [16] wrote a paper demonstrating that Abraham’s form is correct for a nondispersive dielectric media, and that Minkowski’s form, which deals with “crystal momentum”, or “pseudomomentum”, may be used to compute the radiation pressure on objects embedded in such a dielectric media. Gordon’s argument followed the line that ‘radiation’ pressure was a combination of ponderomotive forces exerted directly by the field in the medium, and forces exerted on the medium by the dielectric in the presence of the field. In his 1979 paper [17] in response to Walker, Lahoz and Walker’s experiment [18] Brevik explained why the Abraham force could not be measured directly and why the divergence-free Minkowski tensor was perfectly satisfactory for explaining all existing torque experiments in optics. He noted that a microscopical energy￾momentum tensor can be constructed for a closed system (that is, the field plus matter) and it can be averaged over suitable space-time regions, obtaining terms for pure field or matter plus a number of complicated correlation terms. This means there is no unique way to separate the total energy-momentum tensor into a field part and a matter part. To obtain a definite energy-momentum tensor it is possible to impose extra restriction based on physical arguments, such as the Laue and Moller criterions (that is, that the propagation velocity of the energy of a light wave in a moving body shall transform like a particle velocity under Lorentz transformations) – and if they are applied, Minkowski’s tensor satisfies these criterion while Abraham’s does not. However, Brevik notes that such criteria are a test of a tensor’s convenience rather than its correctness. Brevik was writing at a time when the problem had come back in fashion, and in the previous few years some important work had been done on it, such as the measuring of the Abraham force directly by Walker, Lahoz and Walker [18]. Current experimental trends were moving along both microscopical and macroscopical lines. Brevik believed: ”The microscopical method is advantageous from a fundamental viewpoint, but its drawback is that it easily becomes formally complicated and tends to obscure a simple physical interpretation. The advantage of the simple and less fundamental macroscopical method is its close connection with observation”. At this time Brevik’s interest was lying in the consideration of the electrostriction effect (or the magnostriction effect). He stated that although the electrostriction effect does not affect many experiments it does in special cases, so one should bear its existence in mind and add the Helmholtz electrostriction term to Abraham’s or Minkowski’s tensor whenever necessary. He reinforces this on page 139: “Minkowski’s tensor does not describe electrostriction or magnetostriction. This tensor, therefore, is unable to give a complete description of the local electromagnetic state in the medium.” However, he then continued that it does not matter