The investigations of Lord Rayleigh and Sir William Ramsay had shown that indifference to chemical reagents did not sufficiently characterize an unknown gas as nitrogen, and it became necessary to reinvestigate other cases of the occurrence of "nitrogen" in nature.
Lord Rayleigh had an interest in abnormal psychological investigations, and became a member and vice president of the Society for Psychical Research.
For a popular but authentic account of some of Lord Rayleigh's scientific work and discoveries, see an article by Sir Oliver Lodge in the National Review for September 1898.
In 1875 Lord Rayleigh published an investigation on "the work which may be gained during the mixing of gases."
In the experiment imagined by Lord Rayleigh a porous diaphragm takes the place of the partition and trap-doors imagined by Clerk Maxwell, and the molecules sort themselves automatically on account of the difference in their average velocities for the two gases.