In a previous letter, D. A. Gurnett [1995> discussed the remarkable fact that atmospheric whistlers propagate under the same emission cone relative to the earth's magnetic field as bow waves do with respect to the ship's velocity-namely under 19 ¿28'. The present contribution is a comment on Gurnett's letter and considers a prerequisite for the occurrence of the similarity of both phenomena: the independence of the wave features of parameters such as the ship's speed or the earth's magnetic field. It is found that media with dispersion relations of the form &ohgr;~k&agr; show such independence; a more general solution is also given.¿ 1997 American Geophysical Union