It is an old idea in electromagnetic theory that the æther relations holding in vacuum should also apply in matter. However, this is not commonly used in formulating theories of electromagnetic effects in materials. To be formulated here are theories of magnetic and electric effects in deformable solids based on this idea. It turns out that these are somewhat different from theories in common usage, but it is not easy to determine which is better. In the formulations, some ideas concerning principles of virtual work are used that seem not to be well known.
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