IN NATURE of March 29 (p. 515), Dr. Stoney, in referring to a paper by the writer in the January number of the Astrophysical Journal, raises the question as to the correctness of the use of Maxwell's distribution of velocities in computing the escape of gases from the earth's atmosphere. He maintains that this distribution does not hold at its attenuated limits. In my paper I have not taken conditions which may exist there, but boundary conditions, which are much more favourable to the escape of the molecules of a gas, and certainly compatible with the kinetic theory, if we are to accept such a theory at all.