(1) In the preceding paper the principal arguments are of a general nature, not confined to the case of Brownian particles suspended in a medium; they can be applied to ordinary gas-mixtures. In particular, the equations (7), (13), (44) do not depend on the nature and relative number of the particles considered, nor on the nature of the surrounding medium, provided that (i) the particles retain their individuality, neither breaking up nor combining with others, (ii) no boundary effects are considered, and (iii) a small minimum interval τ0 exists such that in successive intervals τ0 the displacements of any particle are independent. In gases the frequency of molecular collisions is so great that the existence of such an interval is almost self-evident. Its value depends on the extent to which molecular velocities persist after collision. For the molecules in air, under normal conditions, τ0 will not exceed 10-7 second. It is of interest, both from the standpoint of the theory of gases, and as throwing light on the preceding paper, to deal briefly with the application of the above equations to gas-mixtures. The equations of the present note will be numbered in succession to those of the preceding paper.