It was natural that he should then come to the most prominent radio-active elements, uranium, thorium, and radium.

The transformation of the radio-active elements suggestive of the transmutation of metals was perhaps the most interesting idea suggested, but the discussion ranged mainly round the effect which the discovery of radio-activity has had on physics and chemistry in its bearing on the origin of matter, on geology as bearing on the internal heat of the earth, and on medicine in its curative powers.