IN the Literary Supplement of the Times of December 25, 1903, an erroneous statement is on p. 375 placed before its readers, to the effect that our alleged knowledge of the escape of some gases from the atmospheres of planets and satellites is based on an assumed absence of helium from the earth's atmosphere, and has been disposed of by the discovery that helium is present. A brief letter was addressed to the editor of the Times giving proofs that the above statement is incorrect, and from this letter an extract has been published as a note in the next number of the Literary Supplement. The matter concerns one of the great cosmical agencies of nature, and I therefore request you to allow me to deal with the subject in the more adequate way which is permissible when addressing a scientific journal.