SIX BOOKS ON EINSTEIN.* OF the six books before us,

M. Nordmann's' is by far the most important and valuable, though M. Moszkowski's is the most amusing. M. Nordmann presents the Einstein Theory with a clarity and simplicity which no other writer, save possibly Slickman, so far has approached. The Theory of Relativity, which, at first sight, seems to contradict all we know to be real, is, as a matter of fact, based on the only thing which in the last analysis we are logically justified in calling real, namely, experi- ence. It is always thoroughly practical. "The more deeply we study the new physics," says M. Nordmann, "the more we see that it derives almost all its strength from its systematic disdain of all that is beyond phenomena, all that cannot fall

(1) Einstein and the Universe. By Charles Nordmann. London : Fisher Unwin. lies. 6d. net.]--(2) Side-fights on Relativity. By Albert Einstein. London : Methuen. [Ss. 64. net.]—(3) The Theory of Relativity. By Arthur Stanley EddIngton, M.A., F.R.S. Oxford: Clarendon Press. (2s. net.)— (4) A. Criticism of Einstein. By W. H. V. Reade. Oxford : Blackwell. E4s. 64. net.]—(6) Relativity for All. By Herbert Dingle. London : Methuen. (28.] --(6) Einstein the Searcher. By Alexander Moszkowski. London ; Methuen and CO. [12a. 64. net.)

under experimental observation." The same might be said of almost all the aspects of Einstein's Theory. The difficulty which the average man finds in grasping its fundamental idea is due, not at all to any complexity or abstruseness in it, but to a radical difference of outlook. Let us take an example.

An arrow which we hold in our hand is found by measurement to be a yard long. The same arrow, if it could be projected through space at the speed of 161,000 miles a second, would appear to us to be only hall a yard long. What are we to deduce from these two facts ? The average man, whose outlook has been formed on the older science, would say :—" I am aware that the arrow is travelling at the rate of 161,000 miles a second, and I observe that it appears to be half a yard long ; but, since I had it in my hand a minute ago and found that it measured a yard, therefore I know that though it now looks to be only half a yard long, yet it is really a yard." In other words, he accepts the evidence of his senses in the first case, but not in the second.

What does the Einsteinian say ? He accepts the evidence of his senses in both oases. "According to my observation," he says, "(and I have nothing better to rely on) an arrow which appears to be a yard long in my hand appears to be hali a yard long when moving at the rate of 161,000 miles a second. I am not justified in assuming the one observed fact to be truer than the other. I therefore accept both as true." The Einsteinian does not believe that the wooden shaft of the arrow shrinks in some incomprehensible way to half its length ; but his philo- sophical presumption is that all we know of reality is what our senses have told us. If we observe a thing to be so, then we must accept the fact that it is so and not, like our average man, immediately insist, because the fact does not square with our preconceived ideas, that it must " really " be otherwise. For there is no "really" for us beyond what observation tells us.

Now, the great merit of M. Nordmann's book is that it enables the average man to realize the limitations and the lack of justifi- cation in his old outlook, and to understand and appreciate the outlook of Relativism. "And what," the average man may pertinently ask, "is the good of it all when I have appreciated and adopted the new theory ? " The good of it is that it works, whereas the old (except in a rough and riady way) does not ; that it explains ambiguities and discrepancies which, under the old theories, were inexplicable.

M. Nordmann's method is to prelude his discussion of the Theory and its applications by a brief and clear survey of its historical antecedents. He relates the discovery of facts, deductions from them, discovery of other facts contradicting those deductions, and the broaching of theories which reconcile the contradiction. And it is largely because he adopts this historical method that M. Nordmann succeeds in presenting so clearly and logically the philosophical development, the change of outlook, which Relativism involves. Thus, he tells of Brad- ley's discovery of "aberration," from which it was deduced that the ether is not displaced by the earth in its course round the sun ; the Michelson-Morley experiment which seemed to prove that, on the contrary, the earth carried the ether with it ; the Fitzgerald-Lorentz hypothesis which appears as a solution of the dilemma, but which involves consequences so fantastic that they cannot be accepted ; and finally he shows how the coming of Einstein with his Theory solves the problem.

Now, it is precisely in this step from the Fitzgerald-Lorentz hypothesis to the Einstein Theory that the crux lies for the average man, since it involves for him a complete philosophical mite-face. It strikes at his most cherished traditions, his most cherished delusions about reality. It is not recondite nor complex, it is simply a drastic revaluation, and unless we can understand and appreciate this revaluation we shall never grasp Einstein's theory.

M. Nordmann has achieved an astonishing feat. He has practically eliminated mathematics from his book and yet has succeeded in presenting a lucid and profound statement of the Einstein Theory. That he has not been able to simplify com- pletely such an abstruse phase of the subject as the Einsteinian " Interval " is the fault, as Lord Haldane points out in his preface, not of M. Nordmann, but of the theme itself. The conception of a fourth dimension is not, at our present stage of development, capable of being simply presented.

A smaller but more difficult book on two aspects of the same subject is Sidelights on Relativity,2 a translation of two of Professor Einstein's lectures. The first, "Ether and Relativity," defines the nature of ether in accordance with the general theory of relativity ; and the second, "Geometry and Experience," is

an extremely interesting discussion of the distinction between practical awl purely axiomatic .geometry, concluding with an indication that the average man's difficulty with regard to spherical geometry, namely, that it is beyond the scope of visualization and is therefore to him incomprehensible, is not absolute but may be overcome "by using as stepping-stones the practice in thinking and visualization which Euclidean geometry gives us." Both lectures are admirably lucid, but the nature of their audiences made it unnecessary for Professor Einstein to simplify to the extent that M. Nordmann has done.

The Romanes Lecture delivered in Oxford last May by Pro- fessor A. S. Eddington,a whose book, Space, Time and Gravitation, is one of the best studies of the Theory which this country has produced, is another brief and simple exposition of the same subject. It is noticeable that, in distinction to M. Nordmann's conception, Professor Eddington appears to take the view that the Fitzgerald contraction is absolute and not relative.

The reader who, having mastered the philosophical attitude of the Theory and some of its consequences, wishes to test and sharpen his wits, cannot do better than peruse Mr. W. H. V. Reade's little book, A Criticism of Einstein,* and try to lay his finger on its fallacies. Mr. Reade's methods of argument and his use of terms are sometimes extremely bewildering, and he is not, he tells us, deeply versed in mathematics. Hence, in our search for a guide towards Reality, we prefer to plump for Einstein and not for Mr. Reade. Mr. Herbert Dingle's little book, Relativity for All,' would alone provide material for an efficient counterblast to Mr. Resde.

Mr. Moszkowski's book( is of an entirely different species. He is, it appears from internal evidence, an elderly scientist who has for several years systematically Boswellized M. Einstein, for whose character and work he has a most profound admiration.

On opening the book the reader will probably be bored by what • appears to be the biographer's completely adulatory attitude and by the almost comic jargon which Mr. Brose, the translator, and M. Moszkowski between them occasionally produce. As the book progresses, however, the style clears and the reader has the amusement of watching H. Mosz- kowski gradually revealing the sharpness with which he has really been observing his great man. Out of this book, so obviously the product of minds more accustomed to expreas themselves in formulae than in sentences, the curious reader will find that he is gradually able to piece together some extremely interesting psychological facts. The comparison may seem fantastic, but we think those who have read to the end will agree that though it is arrived at from such a different side, there is something in the book which makes it from the psychological point of view rather like a Conrad novel. The scientists of Einstein the Searcher and Mr. Conrad's, seamen have the same preoccupation with exterior facts, something of the same sim- plicity and unselfconsciousness, something of the same nobility in their single-heartedness. Again, as in a Conrad novel (though here by nature not by artifice) we are shown them by fitful touches—they seem revealed to us through an artlessness in the narrator. But perhaps this side of the book is not the one that will strike the reader who comes fresh to the Theory of Relativity, for it is full of the most exciting scientific fairy-tales and imaginings. M. Moszkowski, fortunately for his readers, has a synthetic mind and we see him constantly trying to lure Einstein, that ascetic physicist, on to the Tom Tiddler's ground of metaphysics and to the application of his principles generally. In order so to lure him he makes use of all the entertaining fantasies with which scientists have now began to embellish and embroider the new system of facts which they owe to Einstein. He introduces the reader, for instance, to that most amusing of fictitious characters, Lumen. Lumer is supposed, the reader must know, to leap with a speed greater than light. He exercises his gift by jumping to the moon. When he reaches the moon, he turns round instantly and thus sees himself jumping from the moon to the earth backward. The real value of Moszkowski's book, however, lies in the fact that, though perhaps unconsciously, it attempts to do for Pro- fewer Einstein what we suppose will be done for all investigators in the future. He has given us material for "corrections." Delicate scientific instruments on whose nicety the most import. ant scientific data depend, have their accuracy constantly tested and their variations recorded and allowed for. It is only that most subtle and important instrument of all—the brain of the investigator—which is left uncalibrated and inaccurate. Mid

yet how considerable even in the region of pure science must be the deflections which are caused by this at present unknown quantity, the scientist's subconscious wishes. It seems pretty clear that, striving as they may for complete disinterestedness, all men of science are to some extent aware that they have never quite shaken off a bias toward some opinion or other. If they are often aware that for some ethical reason they are not able to follow the truth with perfect disinterestedness, how often must their operations be subconsciously effected without their knowledge ? M. Mosakowski's book, for instance, would, we believe, give a trained psychologist several clues as to the manner in which Professor Einstein's personal equation has affected the lines along which his investigations have proceeded. For instance, we trace what psycho-analysts are accustomed to call a complex—i.e., a system of half or wholly unoonscious prejudices—in a conversation about occultism. We see in his argument a very slight but quite obvious perturbation ; Einstein has a keen sense of humour, but it is not enough to allow him to consider what he feels is a system of abominable shams, dis- interestedly or unemotionally for a moment.

He is a good musician, his playing of the violin being almost up to concert standard, and he is very fond of improvising on the piano, but dislikes Wagner and many of the later composers. Again, though obviously never taking the brutal German view of the matter, he is yet distinctly an anti-feminist. He is shown giving way to a little ebullition of temper on the fantastic Lumen. Now, might it not be that it is because of this trend of his charac- ter towards what we might call the ascetic and the concrete that he was led to his principle of a finite universe, and still more to his refusal to discuss ramifications beyond his original thesis ?