SOME RECENT SCIENTIFIC BOOKS.*. THE recent advances that have been
made in experimental science have been accompanied by a continual change in atomic theory. Twenty years ago the atom might still have been dismissed as a mere device of chemical explanation. It is now recognized as a physical fact about which there cannot longer be any serious doubt. The most recent work - • (1) The A. ii C of Atoms. By Bertrand Russell. London : Megan Paul. 1[4a. Od. net.)---(2) The Structure of the Atom. By E. N. do C. Andrade. London : 0. Bell and Son. [UM. net.)—(3) Radioactivity. BP K.- FaJans.. London: Methuen. 19a. net.I—(4) The New Physics. By Arthur Baas. London : Methuen. IRA. net.)
is affording still more remarkable results : not only is the atom a physical fact, it is the central fact of modern physics. We had thought that after an Epicurean youth spent in an endless rush through infinite space, it had settled down to a leisured old age of eternal indestructibility, when suddenly it showed a new and most formidable activity. It ceased to be an immutable unit and became a complex whose violent disintegration could be observed.
Such was the enthusiasm with which this rejuvenation was reported that people took alarm. In the minds of many, who had not till them concerned thernselves with it, the atom came to represent a dangerous element in human affairs ; one which in the hands of a careless experimenter might suddenly involve both them and it in a violent end. Together with this alarmist report came also the promise of useful atomic energy. A controlled and less violent dis'ntegration of the atom would one day provide mankind with an unlimited source of power.
These hopes and fears have now given place to a more genuine interest in the subject, but atomic theory is developing so rapidly that our knowledge needs constant revision in the light of the latest discovery, and we are glad to find physicists laying aside their work to provide us with information both of results achieved and theories entertained.
It is a curious fact, however, that in spite of its progress, physics does not seem to be fulfilling the expectations of those who hoped it would reveal the ultimate ingredients of nature. The evolution of physical theory has only been possible through the development of a more elaborate mathematics of space, and we have reached a stage where we might say that physics is nothing more than a complicated kind of geometry. It is the old conclusion, ubi materia ibi geometria. The content of experience has escaped us, and recent work, far from bringing us nearer to it, has rather removed it from us. Though we cannot think of objects without some kind of substratum, yet it is not this that physics reveals to us. Physics tells us of shape, not of stuff ; of form, not of content. It is a morphology, a science of structure not a metaphysics, the science of substance, of Being as such. The assertion that physics can ever yield any metaphysical reality arises from a false distinction between the physics and what at first sight it seemed to represent. When we examine the sciences critically we cease to be able to maintain the distinction between the science itself and its objects. We discover that in a sense they are one. The atom, which we know, can never be that substratum from which we might imagine our experiences to spring. It is essentially a part of scientific knowledge itself, and no more than an incomplete synopsis of experience, primarily intended for further classification.
As the role of mathematical representation in physics becomes more important and the mathematics itself more elaborate, so the task of the writer, who would explain the most recent results to readers who have no mathematical training, becomes increasingly difficult. For this reason we are delighted to find Mr. Bertrand Russell, who is not only a great mathematician, but is also a champion of Scientific Method (even in the field of philosophy), applying himself to a problem for which this method is unquestionably suitable. The A B C of Atoms' is a thoroughly admirable work, by far the best that has been written for the reader who, while not familiar with technical physics, wishes nevertheless to be informed of its latest developments. Mr. Russell gives us a very clear outline of the essential features of atomic theory without introducing the formidable equations that so often produce panic in the mind of the non-mathematical reader. There is very little to be said about a book that is at once so simple, concise and complete, but that it should be read. We have only one suggestion to offer. The author might have given us-the atomic explanation of some of our very familiar experiences. 'Why, for instance, if matter is the open-work of electrons - and nuclei that physics tells us about, is not all matter transparent ? And if we can see through our windows, how is it that we cannot see through our walls as well ?
Professor Andradet gives us a much more exhaustive review of atomic theory. He has studied the subject in great detail, and has the authority of a practical worker. He deals not only with he most popular atom of to-day--that of Bohr and Rutherford—but also with the history of its immediate pre dece.-sors and with the duties required of an atom model. A great quality of his book is that no one view is anywhere dogmatically asserted. For every conclusion the reader is provided with a descriptfre analysis of the line of thought that led to its adoption. though the author gives us the mathematical deduction of some of his results, he is constantly laying emphasis on the principles involved, and thus the argument may be readily followed without any great know- ledge of mathematics. At the same time the book is useful to chemists and physicists who have not attained the degree of specialization required by Professor Sommerfeld's Atomic Structure and Spectral Lines, while for those who wish to pursue further any of the questions raised a valuable list of references is appended to each chapter.
Almost every branch of physics has contributed something to our knowledge of the atom, and that which has perhaps contributed more than any other (and which certainly is the most important historically) is Radioactivity. When in 1896 Henri Becquerel first found that salts of the metal uranium emitted penetrating rays continuously, and without any external influences, a new chapter in physics was opened. This fact, which, at the time, found no place in theory, led to a complete revision of views on the constitution of Matter. The influence of this change has been so great that a study of Radioactivity has now almost resolved itself into a study of a particular aspect of atomic theory. Professor Fajans, in his book,' begins with the transformations and chemical properties of the Radioactive elements, and goes on to show how the most typical property of an element is not its atomic weight (as was thought when the periodic classification of the elements was first made) but the atomic number, which is a measure of the electric charge on the nucleus, and how by the introduction of this concept into physics the results of Radioactivity, X-Rays, Positive Rays and Spectroscopy have been co-ordinated.
A still wider survey of physics is given in Professor Haas's lectures, The New Physics.4 In order to review the subject as a whole, Professor Haas has been obliged to cover a great deal of ground, and has necessarily been able to include only the essential points of the problems raised. He tells us of the great generalizations of physics, the electro-magnetic theory of light, the theory of electrons, molecules, the chemical elements, the quantum theory and the theory of relativity. This, for only six lectures, may seem a most ambitious pro- gramme, but the author's aim has not been to work out the details of these theories, but rather to show how they are related and where disagreement still exists between them. The exposition is lucid and accompanied by many suggestive illustrations. Some technical terms, however, are used in a way that is likely to confuse anyone new to the subject. The "quantum,", for example, is the unit of energy exchange between matter and radiation, and has nothing to do with the unit of electric charge on the electron to which we find the same name applied. We found ourselves also having to unravel "Sextillions of Quadrillions." The use of these terms does not really simplify large numbers. It would have been better always to have written them as powers of ten. In spite of these very minor defects, however, Professor Haas has succeeded in giving us a most illuminating summary of modern views of the universe. Joux PILLEY.
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