Within the atom thousands or tens of thousands of these electrons are moving in orderly arrangement, at terrific speed, round and about one another. The amount of energy required to build up a molecule of any degree of complexity is very great, and it is {72} by the breaking down of complex molecules into simple ones that all our mechanical work is done. And this is not all, for not only can the molecule be thus broken in pieces, but the atom itself is capable of disintegration. "Although we do not know how to break atoms up, they are liable every now and then themselves to explode, and so resolve themselves into simpler forms." "Atoms of matter are not the indestructible and immutable things they were once thought."[3] The idea of the amount of energy thus revealed as available for all kinds of active work is so vast as to baffle calculation and even imagination. It has been said that there is energy enough in fifteen grains of radium, if it could all be set free at once, to blow the whole British Navy a mile high into the air. The thought that we are thus encompassed on every side by pent up potentialities of force, which if uncontrolled might at any moment work our destruction, may well deepen in us the sense of the need, not only for an originating, but for a continually directing mind to superintend the conduct of the universe. We have referred to more than one change of view to which the new discoveries have led. We shall doubtless find that there are other scientific theories {73} which will have ere long to be modified. Already it is recognised that the arguments of Lord Kelvin (he was then Sir William Thomson) and of Clerk Maxwell, which were based upon calculations as to the "dissipation of energy," can scarcely remain unaffected by what we now know, and suspect, of the crumbling and re-forming of atoms. And there are hints abroad of even more revolutionary suggestions. If there has been one principle more imperatively and unanimously insisted upon than another, it has been the uniformity of Nature's laws. What then are we to make of a remark like the following, made by Professor J. J. Thomson, perhaps only half-seriously, to the British Association at Cambridge, in 1904? "There was one law," he said, "which he felt convinced nobody who had worked on this question"--the radio-activity of matter--"would ever suggest, and that was the constancy of Nature." Not less startling is it to be told that a question may yet be raised which will challenge "the conception of a luminiferous aether, which for half a century has dominated physical science. It is possible," so we are informed, "that the field of electro-magnetic energy surrounding an electric charge in motion moves with it, and that the vibrations of light travel through this moving {74} field, instead of through an ocean of stagnant aether."[4]