ABSTRACT
IN 1904 author had the honour of giving an address at the Royal Institution on the subject of radio-activity. The determination of the true character of the a particle is one of the most pressing unsolved problems in radio-activity, for a number of important consequences follow from its solution In conjunction with Dr. Hans Geiger, author have recently developed a method whereby the electrical effect produced by the a particle can be magnified several thousand times. In any case, it is a matter of some interest to be able to detect by its electrical effect a single atom of matter, and so to determine directly with a minimum of assumption the magnitude of some of the most important quantities in radio-active phenomena. The law of radio-active transformation can be very simply and aptly illustrated by an hydraulic analogy.
