Instead of solving the coupled differential equations for \(\textbf{E}(\textbf{r};t)\) and \(\textbf{B}(\textbf{r};t)\) directly, it is more convenient—in analogy to the procedure in electrostatics and magnetostatics—to employ electromagnetic potentials which, however, are not unique. It will be shown that specific gauge transformation are allowed that do not change the physical fields \(\textbf{E}\) and \(\textbf{B}\) .