ABSTRACT
Einstein's paper introducing special relativity was received on June 30, 1905 by the Annalen der Physik, appearing in September. The paper is divided into a "kinematical" and an "electrodynamical" part. Lorentz's 1904 theory and Poincare's further development of it in 1905 retained the ether, and so gave a different interpretation to the Lorentz transformations than in special relativity. In Einstein's kinematical interpretation, the differences between the length and time measurements made by co-moving inertial observers are codified in the Lorentz transformations between space and time coordinates in the different inertial frames of reference. Einstein derived the Lorentz transformations from the two explicit postulates, the relativity principle and the light postulate, the latter now making no reference to the ether. Any theory whose results remain valid under Lorentz transformation is a relativistic theory, while the theory's laws, retaining the same form under such transformation, are called Lorentz covariant.
