With the establishment of the knowledge of a state of physical matter which, as the definition ran, ‘neither results from a combination of other physical substances nor is resolvable into such’, the conviction arose that man’s searching mind had reached ‘rock-bottom’. This conviction, however, was shaken when, with the discovery of radium, an element became known whose property it is to disintegrate into two other elements, helium and lead. Although this did not force science to abandon the element-concept altogether, it became necessary to find a new definition for it.