On the refraction law for a sound ray in a moving medium

A recent paper by D. Hohenwarter and R Jelinek (Acustica - acta acustica 86 (2000) 1-14) states that the refraction law known in the literature for a sound ray in a two-dimensional stratified moving medium is approximate. In that paper, using Fermat's principle of least time, a refraction law for a sound ray is derived which is claimed to be different from those known in t he literature. In the present paper, we show that, in fact, the refraction law obtained by D. Hohenwarter and R Jelinek coincides with those known in the literature. However, these authors were most likely the first to derive the refraction law for a sound ray in a moving medium by using Fermat's pr inciple of least time.