The impedance-boundary condition

Part of the material presented in this article has been collected in the framework of a research activity on the history of ray optics. The aim of this project is collect some reprints of the most-significant original papers of the history of ray optics, from the seventeenth century (i.e., from the work by Rene Descartes) up to now. The purpose of the article is to show that the impedance-boundary condition (IBC)-usually referred both in western countries and in the former USSR as the Leontovich condition was also derived independently by another Russian scientist, A.N. Shchulkin. He published the IBC in 1940, in his book, Propagation of Radio Waves.