To explain further. Radio-active bodies are composed--according to Rutherford's plausible hypothesis--of atoms in unstable equilibrium. The gradual changes incidental to their own internal activities suffice to bring about their disruption. And their explosive character is obviously connected with unwieldy size, since uranium, thorium, and radium, the three substances pre-eminent for radio-activity, possess the highest atomic weights known to chemistry. The precarious balance, then, of each of these complex, though infinitesimally small systems is successively overthrown, regardless of external conditions or environment, their constituent parts being hurled abroad with the evolution of an almost incredible amount of energy. Their products include cathode-rays; matter in the 'fourth state,' matter a thousand times finer than hydrogen, is ejected in torrents from the self-pulverized atoms of radium. Moreover, the issuing rays are equivalent to currents of negative electricity. Each corpuscle bears with it an electron, or is itself an electron, for the choice between the alternatives is open. In either case, we are confronted with matter apparently in its ultimate form; and to that form ordinary, substantial bodies tend to become reduced. Electrons may fairly be called ubiquitous. They occur in flames, near all very hot masses, wherever ultra-violet light impinges on a metallic surface;[61] they are freely generated by Röntgen and cathode-rays; they are the agents of electrical transmission in conductors. Everywhere throughout the universe, atoms are thus in course of degradation into corpuscles. But no information is at hand as to the scene or mode of their reconstitution. The waste and decay are patent; the processes of compensation remain buried in obscurity. Indeed, Sir William Crookes anticipates the complete submergence, at some indefinitely remote epoch, of material substance in protyle, the 'formless mist' of chaos. He assumes an identity between the past state and the future, leaving, however, the present unexplained. The break-up of matter, in fact, does not render its construction the more intelligible. Running-down is an operation of a different order from winding-up. It is an expenditure of a reserve of force. It needs no effort; it accomplishes itself. But to create the reserve for expenditure demands foresight and deliberate exertion; it implies a designed application of power.