The paper discusses the problem of equality of Inertial frames of reference IFR. The hypothesis of a physical ether, whose properties do not depend on the choice of an inertial reference frame, is proposed. Based on the concept of the physical ether, it turns out the features of instantaneous action at a distance. It is shown that there is a class of transformations that preserves Maxwell’s equations unchanged. The problem of choosing a transformation is posed. This choice should be based on experimental research.