"It has been suggested that the extent of the dark space represents the mean free path of the molecules.... It has been pointed out by others that the extent of the dark space is really considerably greater than the mean free path of the molecules, calculated according to the ordinary way. My measurements make it nearly twenty times as great. This, however, is not in itself a fatal objection; for, as we have seen, the mean free path of an ion may be different from that of a molecule moving among others."—Schuster, Proc. Roy. Soc., xlvii., pp. 556-7.
"Physical Memoirs," part ii., vol. i., p. 244. The paragraph is italicized in the original.
Loc. cit., p. 242.
In a valuable paper read before the Royal Society, November 20, 1890, by Professors Liveing and Dewar, on finely divided metallic dust thrown off the surface of various electrodes, in vacuum tubes, they find not only that dust, however fine, suspended in a gas will not act like gaseous matter in becoming luminous with its characteristic spectrum in an electric discharge, but that it is driven with extraordinary rapidity out of the course of the discharge.