THE INTERPRETATION OF RADIUM.*
THE aspect of science chiefly impressing those who looked at it from the outside used to be, perhaps, its rigidity. It was not always distinctly realised that this apparently impassive and inflexibly advancing science is, viewed as a whole, a highly organised and consequently sensitive growth of the human mind, and exposed like the human mind itself to shocks which must affect its vital equilibrium, and deeply modify its whole future conceiving of things. How far the latter estima- tion of science is gaining ground, and to what pregnant issues, this is not the place to inquire. But one is reminded of it by the stimulating shock to one side of the very responsive scientific constitution that has come, appropriately enough, from the discovery of the radio-activity of certain
elements.
The new situation is illustrated by Mr. Soddy in his Inter- pretation of Radium with his usual lucid aptness when he says: "If anyone were to demonstrate to an architect that the bricks he habitually and properly employs in his constructions were under other circumstances capable of entirely different uses—let us say, for illustration, that they could with effect be employed as an explosive incomparably more powerful in its activities than dynamite—the surprise of the architect would be no greater than the surprise of the chemist at the new and undreamt-of possi- bilities of matter demonstrated by the mere existence of such an element as radium."
The illustration is no chance one, but is pointedly significant, for the whole question with which we are face to face may roughly be put by asking : Is matter quite generally explosive ? We are accustomed to look upon explosiveness as a property of certain special kinds of matter, like gunpowder or nitro- glycerine. And the property, when analysed, comes to this : that the composition of the special matter is such that on certain occasions it will undergo sudden change, and in this change will release copious stores of energy which under its previous conditions of composition had been locked up. Now the new question is whether matter generally, however inertly settled its constitution may seem, is really susceptible of changes in inner structure,—changes, indeed, of an immensely finer order than those assumed in explaining explosions, and changes which would be accompanied by relatively prodigious outbursts of escaping energy, revealing what a secret reservoir matter had always been.
This wide question is prompted by the known behaviour of those particular forms of matter which are called radio-active. The so-called " rays " emitted by these substances exhibit certain electrical and heat effects ultimately far more sig- nificant, if at first less striking, than their arrestive photo- graphic and phosphorescent manifestations. Half-a-grain of radium will in about three and a half days produce as much heat as would be evolved by the complete combustion of the same weight of coal. But while the coal, burnt and con- sumed, is in a short time "no longer coal," the half-grain of radium goes on pouring out heat energy year after year, and is expected ultimately to have given out two million times as much energy as could be derived from the burning coal. The investigations in which Mr. Soddy has himself been directly
* The Interpretation of Radium: being the Substance of Siz Free Popular Erperimental Lectures delivered at the University of alas9oro,1608. By Frederick Roddy, M.A. London: John Murray. [6s. net.] and practically concerned lead him to conclude that what is really happening is not without analogy to what is already familiar to us in the case of explosive substances,—thus far, at any rate, that energy previously locked up in the substances is being released in a way of sudden and forcible outburst. Yet, sudden in one sense, it is very gradual in another, for the change does not come over all the mass at once, but over a very small proportion of its atoms in each moment. The chemical atoms, of course, have strangely opened up to us of late ; to our present insight they are no more absolutely single particles than the solar system itself (to which, indeed, their structure has been supposed to bear a curious analogy) is a single body. And the theory with which Mr. Soddy, in association with Professor Rutherford, has presented us is that the radio-active manifestations of radium are due to the sudden disintegration of the atoms of the substance; then again of the new kinds of atom, which are of slightly reduced mass, left after this disintegration; and so on through a series. The disintegration, at certain points in the series, involves the dismission of a flying material particle that darts off, in given cases at a rate of over twelve thousand miles a second, to contribute to the making of what are known as the a-rays of radium.
The question then comes to be,—How far is this violent breaking up of the atom, with the sudden emission of a projectile capable of doing work, the effects of which can be made actually visible to us, peculiar to what we know as the radio-active elements ? The visibly agitated members of a company may sometimes not be so altogether peculiar in it as they seem; they may be peculiar only in the minor respect of showing plainly a tension and disturbance which are at bottom common to them and their companions. Is this the case with radio-active elements, and the wider range of apparently quieter and more stable ones ? If we let Mr. Soddy discuss this question with us, we shall find ourselves in a beautifully woven net of argument, the intricate but perfectly clear meshes of which exhibit a high degree of scientific strength, independently of their attachment to this particular point of interest.
For one thing, radio-active elements certainly do not appear to be isolated from the rest of the scheme of Nature by their general chemical characteristics. And it is shown by refer- ence to Professor Rutherford's researches that the expelled particles of matter might be undergoing continual projection from other forms of matter at any speeds under five thousand miles per second without being perceptible in any way. Their tiny mass renders them dependent on their momentum for self- revelation. With a light touch of mathematics, just enough to make it apparent how engrossing the pursuit must be to the initiated, without putting too heavy a strain upon the attention of the uninitiated, it is brought out that the average period of settled life for the atoms that are severally disintegrating in a mass of uranium to form the radium atoms may be put at seven thousand five hundred million years, while that of the radium atom is given at only two thousand five hundred years, and that of the atom of one product of disintegrating radium at only 4.3 minutes. Thus in uranium we may have something intermediate between the lively radium and elements pre- sumably more stable than either. There are various degrees of stability. Perhaps the gold of our markets may be rare in Nature, and therefore valuable, just on account of a disposition of its atoms—no doubt in immensely protracted order—to go to pieces, and (as gold) to disappear. Mr. Soddy, it will be perceived, by no means thinks with his eyes altogether upon the ground. " If it were possible," he says, " artificially to disintegrate an element with a heavier atom than gold, and produce gold from it, so great an amount of energy would probably be evolved that the gold in comparison would be of little account. The energy would be far more valuable than the gold." And if we suppose that radio-activity, with its series of transmutations, forms but a specially vivacious and favourably staged example of what is generally going on, a vision of illimitable vistas opens up before us. Instead of dwelling, with the physicists of a few years ago, on the decaying energies of the universe, we may follow our author's brilliant dream of deeply and yet more deeply reserved resources imprisoned in its substance, and waiting their moments, here early, there enormously delayed, to be set free. But whether we ourselves shall ever be able to set them free in more rapid flow, and so to control them as to affect
the conditions of our own existence,—that is the practical question. Our author is sanguine, and even suggests the future abolishing of that tragic struggle for existence which depends upon the scarcity of available energy. But it has to be confessed that, in spite of the rapid growth of our know- ledge of the scientific significance of radio-activity, our power to accelerate or retard its courses is absolutely nil. And in a situation without scientific parallel on the one hand, or hint of practical development on the other, we cannot be sure bow far the hopeful analogies that crowd upon us from past achievement will prove to apply. But uncertainty does not lessen the interest of an enterprise.
We have not dwelt specially on the startling aspects of speed, of minuteness, and of number that are associated with the study of radio-activity. To give special prominence to these in a brief review would perhaps he an injustice to a most admirably conceived exposition which does not seek merely to attract us by turning marvels, at once outstripping our imagination and humbling our conception into cheap popular gazing-stocks, but rather supports its unfailing charm by the legitimate interests—pointed here into a fascination that may arrest even an habitually desultory reader—of science at once genuinely and delightfully taught.
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