[en] Upon the consideration of a superconducting ring interrupted by a barrier and the use of Wilson–Sommerfeld quantization rule along with some fundamental facts of electrodynamics and characteristic properties of the superconductive state, we give a short proof of Josephson’s voltage-frequency relation and we establish, in a simple manner, the dependence of Josephson’s critical current on the magnetic flux. The original insights into the derivation, due to their elementary and intuitive character, as well as the link they provide with the old quantum theory, will allow the reader to understand the peculiarities underlying the Josephson effect. (paper)