expression " Radiant Matter," or matter in the ultra-gaseous state, to explain the novel phenomena of phosphorescence, trajectory, shadows, mechanical action, magnetisation, and intense heat. " In studying this fourth state of matter," I said, " we seem at length to have within our grasp and obedient to our control, the little indivisible particles which with good warrant are supposed to con- stitute the physical basis of the universe. We have seen that in some of its properties radiant matter is as material as this table, whilst in other properties it almost assumes the character of radiant energy. We have actually touched the borderland where matter and force seem to merge into one another."*
In twenty-five years one's theories may change, although the facts on which they are based remain immovable. What I then called " Radiant Matter " now passes as " Electrons," a term coined by Dr. Johnstone Stoney, to represent the separate units of elec- tricity, which is as atomic as matter. What was puzzling and unex- plained on the " Radiant Matter " theory is now precise and luminous on the " Electron " theory. Thus my early hypotheses fall into order by the substitution of one expression for the other. A chemical ion consists of a material nucleus or atom of matter constituting by far the larger portion of the mass, and a few electrons or atoms of elec- tricity. The electrons are the same as the "satellites" of Lord Kelvin and the " corpuscles " or " particles " of J. J. Thomson.
Electrons probably leave the negative pole with a velocity nearly uniform, modified to a considerable extent by the degree of exhaustion, and to a less extent by the electromotive force behind them. Many experiments the details I must leave to a future occasion show that the liberated electrons do not behave as a gas, >., they have not properties dependent on inter-collisions, mean free path, &c. ; they act more like a fog or mist, are mobile and carried about by a current of air to which they give temporary conducting powers, clinging to positively electrified bodies and thereby losing mobility, and settling on the walls of the containing vessel if left quiet.
On the other hand, the crowd of hydrogen or mercury atoms, by virtue of molecular motion and inter-collisions, act as gases. Whilst their mean free paths are conditioned by the degree of exhaustion, there may be amongst them a certain numlxjr of actwil free paths differing widely on each side of the mean. Under the influence of the electro- motive force, and at the right degree of exhaustion, these atoms arrange themselves in groups,! while the rushing swarm of electrons
- ' Chemical News,' vol. -AO, p, 130.
t In an address delivered before the Institution of Electrical Engineer*, January 15th, 1891, I gave an outline of a theory of stratifications in rarefied gases. The following quotation renders my meaning clear : " If, in any much fre- quented street, at some time when the stream of traffic runs almost equally in both directions, we take our stand at a window from which wo can overlook the passing
