are questions of a higher order of difficulty than those which occupy us to-day, and it must remain for a future Romanes Lecturer to report progress in these directions, whenever adequate progress has in fact been made.
8. That is the end of the first half of my lecture; and six months ago that, somewhat expanded, might have been the whole of it, because the next portion would have seemed too fanciful; but discoveries have been made, chiefly in France and in Canada,—some of the most striking of them within the present year,—which remove the treatment of the next part of my subject from the realm of fancy to the region of probability, and justify my proceeding further with some of the theoretical consequences deducible from an electric theory of matter.
I referred above briefly to the origin of radiation, saying that by the method of applying a powerful magnet to a source of light, and examining the minute perturbations in the lines of the spectrum thus produced, it had been proved that the real source of radiation was an electric charge in rapid orbital motion; and I now go on to say that by careful measurement of the amount of perturbation it has been definitely proved that it is our friends the negative electrons, with a mass about one-thousandth of the smallest known atom of matter, that are responsible for the excitation of ether waves or the production of light. Larmof and others have indeed shown mathematically that whenever an electric charge is subject to acceleration, an emission of some amount of radiation is inevitable, by reason of the interaction of its electric and magnetic fields; and
