MODERN PHYSICS.

(1) Studies in Radioactivity. By Prof. W. H. Bragg, F.R.S. Pp. xi+ 196. Macmillan's Science Monographs. (London: Macmillan

and Co., Ltd., 1912.) Price 5s. net. (2) The Electrical Properties of Flames and of Incandescent Solids. By Prof. H. A. Wilson, F.R.S. Pp. vii+119 (London: University of London Press; Hodder and Stoughton, 1912.) Price 6s. net.

IT

T is seldom in the history of any science that three fundamental discoveries are included within the brief space of three years. The discovery of X-rays in 1895 marks a new epoch in the history of physical science, for it led early in 1896 to the discovery of radio-activity and was followed in 1897 by the proof of the nature of the kathode rays and the advent of the electron as a definite entity. In the following years an ever-increasing fraction of the energy of workers in physics has been devoted to a study of the numerous important problems which have arisen from these three primary discoveries.

In the early stages of the experimental inquiry a discussion of these subjects was conveniently included in single treatises on the conduction of electricity through gases and on radio-activity. With the rapid increase of our knowledge of the various subdivisions of the subject it was inevitable that special treatises would be necessary to discuss in more detail the results of recent investigations. This is illustrated by the separate publications that have appeared on the theory of electrons, ionisation by collision, and the chemistry of the radio-active bodies. This tendency towards specialisation is in many respects advantageous provided two conditions are fulfilled. In the first place, it is essential that the subject should be treated by experts who have taken an active part in the development of our knowledge of the topics under consideration; in the second place, it is of great importance that the author, in the extended treatment of the subject, should not lose sight of its connection with the main stream of advance in physics, both experimental and theoretical.

The two books under review fulfil these conditions in an ideal manner, for they are both written by men who have made notable contributions to our knowledge of the subjects under consideration, and have that requisite knowledge of modern physical views to treat the subjects in the right perspective.

(1) The work of Prof. Bragg deals mainly with the phenomena accompanying the passage

of a, 6 and 7 rays and X-rays through matter. An interesting account is given of the theoretical reasoning that led the author to predict the nature of the absorption of the a rays by matter, and of the admirable experiments made by him which led to such an important extension of our knowledge of this subject. The results of experiments on the passage of X-rays through matter are interpreted on his well-known corpuscular theory of the X-ray. The essential point of this theory is that the energy of the X-ray is corpuscular in the sense that it is concentrated and does not spread from the source like that to be expected in an ordinary pulse or wave. In addition, it is supposed that the B ray and the X-ray are mutually convertible forms of energy. When a B ray disappears as a result of a close encounter with an atom, an X-ray of equal energy takes its place and tends to be propagated in the original direction of the B ray. This theory has the advantage of giving a concrete and easi grasped idea of the processes occurring in the passage of X-rays through matter, and has served a very useful purpose in directing numerous investigations which have thrown much light on the subject.

It is remarkable that although more than seventeen years have elapsed since the discovery of X-rays, there is still a great difference of opinion as to their nature and the mechanism of their absorption by matter. The recent striking experi ments of Laue and his colleagues, supplemented by the explanation of Mr. W. L. Bragg, seer: to show conclusively that a fraction of the X-rays suffer regular reflection at the crystal planes of mica and of other crystals. These results seem only compatible with the view that the X-rays are some type of wave motion. On the other hand, the liberation of a high-speed electron from an atom traversed by the X-ray cannot be explained with any credibility unless it be supposed that the energy of the X-ray is concentrated over a minute volume, and can be given up in an encounter with a single atom. These apparently conflicting but fundamental properties of the X-ray must be reconciled in any satisfactory theory of the X-rays.

The book is very pleasantly and clearly written and contains a concise account of most of the important experiments on the subject under coasideration. While there will, no doubt, be considerable difference of opinion as to the merits of the theories proposed by the writer, the book can be strongly recommended not only to the physicist, but to all those who are interested in the fascinating field of inquiry which has been

(2) The work of Prof. H. A. Wilson is confined to a discussion of the electrical properties of incandescent bodies and of flames. Under the influence of the ionisation theory of gases this important field of inquiry has rapidly developed, and a large amount of experimental data has now been accumulated. An account is first given of the character and conditions of the discharge of negative and positive electricity from glowing bodies, followed by a discussion of the conductivity

of flames under different conditions. It has been clearly established that the rapid discharge of electricity from hot bodies is due to the escape of free electrons, and the author discusses the result in the light of the theory developed partly by himself and partly by Prof. O. W. Richardson., This theory supposes that the free electrons in a metal acquire sufficient velocity at high temperatures to escape from the metal and to give rise to the observed discharge of negative electricity.

The earlier experiments certainly afforded strong ground for this conclusion. Since the publication of this book, however, experiments have been made by Pring and Parker and others which throw same doubt on the completeness of this explanation. It has been shown that carbon at very high temperatures and in a thoroughly exhausted space gives only a minute fraction of the current to be expected from the application of the theory to the earlier measurements at lower temperatures. There seems to be little doubt that, at any rate in the case of glowing carbon, the large electronic currents initially observed were due not to the escape of electrons in the carbon itself, but rather to some interaction between the carbon and the residual gases. The theory of the subject is at present in a somewhat unsatisfactory state, and it would appear that more complete experimental data are required before any theory can be adequately tested.

By

(3) Evolution and the Need of Atonement. Stewart A. McDowall. Pp. xvi+ 155. (Cambridge University Press, 1912.) Price 3s. net. (4) On the Consciousness of the Universal and the Individual. By Dr. F. Aveling. Pp. x+ 255. (London: Macmillan and Co., Ltd., 1912.) Price 5s. net.

(5) Science and the Human Mind. By W. C. D. Whetham, F.R.S., and Catherine D. Whetham. Pp. xi+ 304. (London: Longmans, Green and Co., 1912.) Price 5s. net.

(6) The Note-Books of Samuel Butler, Author of Erewhon." Selections arranged and edited by Henry F. Jones. Pp. xii+438. (London : A. C. Fifield, 1912.) Price 6s. net. (7) The Spiritual Interpretation of Nature. By Dr. J. Y. Simpson. Pp. xv+383. (London : Hodder and Stoughton, 1912.) Price 6s. net. (8) Papers on Psycho-Analysis. By Dr. E. Jones. Pp. xv÷432. (London: Baillière, Tindall and Cox, 1913.) Price 10s. 6d. net.

(9) Questions of the (9) Questions of the Day in Philosophy and Psychology. By Dr. H. L. Stewart. Pp. x+ 284. (London: Edward Arnold, 1912.) Price Ios. 6d. net.

(1) DESCRIPTION,

A

Prof. Wilson gives a brief but concise account of the important experiments on the subject, followed in every case by a discussion of the results in the light of the theories proposed. An excellent description is given of the experiments on flames with and without the additions of salt vapours, and the results are interpreted in terms of the ionisation theory. The author himself was a pioneer in this field and laid the foundation of the present theory on a firm basis of experiment.

The book is in no sense popular, but is written for the advanced student or investigator who is already familiar with the fundamental facts of the electronic theory and the ionisation theory

historical and biological, of the feminist movement. The conclusions of the author, who is a London University Extension lecturer on biology and sociology, are: that woman, not being merely a female man, but of different aptitudes, has her own proper sphere and direction of development; that her speciality is motherhood-not merely the physical fact, but also the ennobling influences involved; that the married woman should not work in factories, &c., but should be economically dependent on the man, as he is domestically dependent on her; and that a standard marriageable wage should be secured to the male worker. The book closes with a reprint of W. C. Roscoe's article, "Woman," in The National Review for October, 1858. In this pioneer essay, "every

argument of real strength for and against the woman's movement, that has been used in the fifty odd years that followed its publication, will be found summarised."

(2) A good text-book, more than elementary and well adapted for its purpose as a guide to teachers. It follows James and McDougall for the most part, and is provided with suitable questions at the end of each chapter. Its scheme

is the usual modern one: first, the physiology of sensation, then perception, imagination, ideation, memory, conation, feeling, instincts. Throughout, the practical application to the child-mind is kept in view, and the writing is clear and good. Mr. Dumville is master of method and lecturer on education in the L.C.C. Islington Day Training College.

(3) Mr. McDowall accepts the scientific view of biological evolution, carrying it forward to a higher plane. He suggests that the fact of spiritual development demands a determining environment to call out spiritual activities. This he conceives as a transcendent mind which comprehends, enfolds, includes the environment-sum of the whole world. Man, however, has sinned, being free; and his only way of salvation is to "accept Christ "-though if he fails to do so in this life he may have a chance in the next. Bishop Ryle supplies a eulogistic introduction to the book, which is thoughtful and earnest, and will doubtless be of use to many readers who feel the need of harmonising theology with natural science.

(4) Dr. Aveling sketches the history of the problem of universals or general terms-i.e. roughly speaking, what "man" means, apart from this or that man-from Plato down to the present, and then proceeds to give a detailed account of his psychological experiments. These were carried out with pictures and nonsense-words, with various observers. The results led to the conclusions among others--that images are not necessary as contents for thought, but thinking always involves concepts as contents; and that "the universal' is phenomenologically present, or tends to be present, to consciousness as a concept or imageless substantive content." The research was, of course, psychological, aiming at answering the question: "What is discoverable in consciousness when we think the universal'

or the individual'?" The metaphysical question ("Do universals exist in nature?") and the epistemological question (“Do our universal ideas correspond to reality?") are naturally left to their respective domains.

(5) Mr. and Mrs. Whetham have once more

produced an admirably readable yet trustworthy popular-science book, and it is to be hoped that it will circulate widely. The authors trace the development of science from its dim beginningsdim so far as history is concerned-in Chaldea and Egypt, down through Aristotle, the Arabians, Aquinas, and the Renaissance, to the Baconian period and the present day-including even such recent events as Prof. Schäfer's Dundee address. As becomes a historical survey, dogmatism and partisanship are avoided, the authors refraining from expressions of opinion on, e.g., vitalism. The style is enlivened by a pleasant humour, as when the Council of Nicæa is said to have met, "with characteristic modesty, to determine the true nature of God" (p. 67), and the sequence of the book is logical and smooth. Its philosophy also is excellent, and many men of science might do worse than read the last two chapters on the scope and function of science, and its relation to religion. The "laws of nature" are the logical laws of the conceptual world formed by our own minds, and these laws are of practical use in enabling us to predict the future behaviour of our own perceptions. The business of science is to construct a consistent conceptual model, but how far that model corresponds to "reality" is not for science to say, nor can it be assumed to represent reality in any final or total way. In short, there is room for metaphysics and faith by the side of science.

(6) The whimsical genius of Samuel Butler is best known through the satirical romance “Erewhon," but his "Life and Habit" and "Unconscious Memory "show him as a serious thinker, of scientific methods, but with a spiritual and teleological view of evolution, in which he was in advance of his time. But his title to fame will probably rest on his literary style and the flashing audacity and originality of his thoughts. This is specially indicated in the volume under notice, which consists of detached and fragmentary notions, jotted down at odd times, on all subjects, from Handel to death, from mind and matter to painting. His criticisms are cruelly searching, as when he compares Pater's style to an old woman who has had her face skilfully enamelled. It is a good book to dip into when seeking smart paradoxes. We recommend it to Mr. G. K. Chesterton, of whom Butler often reminds us. Mr. Chesterton will rightly take this as a compliment when he reflects that his friend G. B. Shaw has called Butler the greatest English writer, in his own department, of the latter part of the nineteenth century.

(7) A very similar book to Mr. McDowall's

above-noticed, but on a larger scale and more detailed in its sketch of biological evolution. Dr. Simpson is orthodox in his science, but on the religious side conceives a World Principle immanent and transcendent, yet personal. "Of course, we cannot form a clear conception of such infinite, unconditioned personality. We are certain that it is something richer in content than our personality." The problem of sin is very well handled the Genesis narrative is symbolically true, but does not teach that man fell from a state of goodness. On the contrary, he has risen from a state of innocency, such as the child's state before he learns to recognise good and evil. He must continue to rise, until he reaches communion with God through likeness to Him. The book contains much that is theologically and philosophically debatable, but is an excellent example of the modern literature of reconciliation, and does credit both to the learning and the piety of its author.

(8) Dr. Jones dedicates his book to Prof. Freud, among whose disciples he enrolls himself. Many interesting illustrations are given, showing the influence of subconscious desires in producing lapses of memory and the like. Other chapters deal with the relation between organic and functional diseases, simulation in hysteria, the pathology of morbid anxiety, the action of suggestion in psychotherapy, Freud's theory of dreams, and psycho-analysis and education. The writer is associate-professor of psychiatry in the University of Toronto. His book is extremely readable and good, chiefly by reason of its wealth of concrete examples. We may incline to think that the Freudian psychology is itself obsessed with sexideas, and is guilty of tracing everything to subconscious sexual thoughts or desires; but, after all, a theory is best tested by its thorough application to facts, and there is no doubt that Freud is a pioneer, comparable-it may be, as Dr. Jones suggests-with Darwin himself.

(9) These essays are, in the main, an expansion of a course of lectures delivered in the Queen's University of Belfast. They deal with subconsciousness, genius, pragmatism, pessimism, Nietzsche, &c. The opinions are well and temperately stated, and we only discover one dubious. statement of fact-viz., that 98 per cent. of all classes of persons are hypnotisable. This percentage is much higher than the average opinion of experts would allow. The author follows Myers in his psychology, according well-merited praise to that writer and to the careful work of the Society for Psychical Research.

J. A. H.

MATHEMATICAL TEXT-BOOKS.

(1) Exercises in Modern Arithmetic. By H. Sydney Jones. Pp. x+336. (London: Macmillan and Co., Ltd., 1912.) Price 2s. 6d. (2) Notes on Algebra. By A. F. van der Heyden. Pp. viii+133. (Middlesbrough: Wm. Appleyard and Sons, Ltd, 1912.) Price 2s. 6d. (3) The Teaching of Mathematics in Secondary Schools. By Arthur Schultze. Pp. xxi + 370. (New York: The Macmillan Company; London: Macmillan and Co., Ltd., 1912.) Price 55. 6d.

THE

(1) HIS volume consists of the examples reprinted from the author's work entitled "Modern Arithmetic with Graphic and Practical Exercises." The range covered is that required for the Oxford and Cambridge Local examinations. The quality of the examples, which are mainly of a practical character, is good. A number of typical examination papers are given at the end of the book.

(2) This note-book is intended for students who are revising the subject, not for those breaking new ground. There is much interesting historical information; but we are inclined to think that the treatment is scarcely sufficiently thorough for many purposes. For example, none but the simplest tests of convergence are given, the theory of numbers is represented by Fermat's theorem alone, and the method given for resolving partial fractions is inadequate. The geometrical representation of complex numbers, Demoivre's theorem and its applications are included.

(3) The object of the author in publishing this volume is to show that the purpose of a mathematical training is best served by making the course less informational and more disciplinary than is at present customary. He contends, and