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Xerophytic Native Grasses, the Anatomical Structure of some, E. Breakwell, 553 X-ray: Bulbs, Production of, in France, 653; Fluorescence and the Quantum Theory, Prof. C. G. Barkla, 7; Technic, a Manual of, Capt. A. C. Christie, 87 X-rays Dr. G. W. C. Kaye, 87; and Crystal Structure, Prof. W. H. Bragg and W. L. Bragg, 198; and Crystalline Structure, Prof. W. H. Bragg, 109; and Crystals, Dr. A. E. H. Tutton, 198; Dosage of, E. Coustet, 436

Yale College, Bequest to, 248; University, Bequest to, 223 Yellow Sensation, the Simple Character of the, Dr. F. W. Edridge-Green, 547

Yenesei: a Summer on the, (1914), Miss M. D. Haviland, 209; Ornithology in Delta of, Miss M. D. Haviland 78 Yosemite National Park, Gift for the Survey of the Animal and Bird Life of the, 693

Youth, the Value of, as a National Asset, 457

Zeolites and Associated Minerals from the Tertiary Lavas around Ben More, Mull, W. F. P. M'Lintock, 637 Zeppelins and other Enemy Aircraft, All about, F. Walker, 588

Zinc-copper Alloys, O. F. Hudson, 157

Zoological: Monographs, 143; Nomenclature, 153; Nomenclature, the Rules of, Dr. F. A. Bather, 118; Society of London, additions to, 14, 460; and the War, 271; Monthly General Meeting of the, 653; Society of Philadelphia, Forty-third Annual Report of, 350; Society of Scotland, Second Annual Report of the, 546

Zoology: an Elementary Text-book. Dr. A. E. Shipley and Dr. E. W. MacBride, third edition, 476; Elementary, 476: Systematic, Pencil and Pen in, Rev. T. R. R. Stebbing, 584

PRINTED IN GREAT BRITAIN BY

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THURSDAY, MARCH 4, 1915.

TIME AND SPACE.

A Theory of Time and Space. By A. A. Robb. Pp. vi+373. (Cambridge University Press, 1914.) Price 10s. 6d. net.

THE

HE appearance of Dr. Robb's treatise, if such a word can be applied to a volume which opens out a new field of philosophical inquiry on the basis of modern physical science, is a very welcome event, and more especially to students of the fundamental nature of the conceptions which we employ in our attempts to describe physical experiences. There is a general feeling, at least in this country, that in spite of the remarkable success of the principle of relativity in simplifying our descriptions of physical science, the more logical aspect of the principle is seriously at fault, and herein lies the reason for the noticeable decline in favour which the principle has experienced recently. The present work, as its title implies, is a definite theory of space and time, and although its aim is strictly logical throughout, it deals with its subject in a simple geometrical manner, readily followed by anyone who has made a study of Euclid. The author's selection of a model is very judicious, and makes the argument flow so smoothly that the reader will probably realise with a shock, at some point, the far-reaching nature of the conclusions to which he has been led.

The author had already published the introduction to the work as a tract, but it is reproduced in the present volume. It gives a brief statement of the history and essential meaning of the principle of relativity, pointing out the more important difficulties which are felt, and which the more formal treatises on the principle, by tending to emphasise unduly the purely mathematical aspect,

1

do not attempt to meet. As is well known, gelativity demands that events which are simultaneous events for one observer are not necessarily so for another. This is at variance with the fundamental principles of logic, which demand that "a thing cannot both be and not be at the same time." But the simplicity brought about by the introduction of such postulates is such that physicists have allowed them to pass for a time, always, however, realising that our ideas of space, and more especially of time, must be so modified as to make them intelligible and part of a logical system. This simple example will illustrate the scope of Dr. Robb's work, and the exact manner in which it differs fundamentally from the more usual treatises. He has shown that, as a corollary from his treatment of space and time relations, such a logical scheme of geometry and of time can be built up, in which our ordinary geometries find a place.

The foundation of the work involves a new idea -that of conical order. The spacial relations are to be regarded as the manifestation of the fact that elements of time, or instants, form a system in conical order. This conception may be analysed in terms of the relations of after and before. From some twenty-one postulates involving these relations it is possible to set up a system of geometry in which any element can be represented by four co-ordinates, x, y, z, t. The first three correspond to space co-ordinates, and the fourth to time as generally understood. But since an element in this geometry corresponds to an instant, and bears the relations of after and before to other instants, the theory of space appears as a part of the theory of time. Simple geometrical interpretations of the initial postulates in three dimensions are given in the volume. One remarkable feature is that it seems necessary for a really consistent theory to limit the number of dimensions to four. The geo

metrical system is developed to a considerable extent, and is left at a point from which it may be easily carried in its correspondence with the whole range of ordinary geometrical detail.

The investigation is made in connection with the phenomena of optics. This is, of course, necessary in any attempt to analyse the foundations of any space and time theory. The view taken is that the axioms of geometry are mainly the formal expression of certain optical facts, and the author rightly points out the defects in systems some of the axions of which have this significance, while others depend on such things as the properties of. purely ideal rigid bodies. The significance of all axioms in a logical scheme must be of the same character, and the optical character is the only legitimate one we have at our disposal:

It is not possible in a review to give any account of the detailed working out of these ideas. It can only be said that their development is extremely elegant, and is worthy of being taken as a model for any type of geometrical work. The book is in the standard form of the Cambridge University Press, and bearing in mind the traditional excellence of this series, it is perhaps superfluous to say that the tradition is well maintained in the present case.

APPLIED MECHANICS AND AMERICAN

TIMBERS.

The Mechanical Properties of Wood. By Prof. S. J. Record. Pp. vi+165. (New York: J. Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1914.) Price 7s. 6d. net.

T

O those unfamiliar with the composition and construction of wood it comes as a matter of surprise that the "hardness," calorific value, also, to some extent, the strength and certain other mechanical qualities, are proportional to the apparent specific gravity. Yet the unexpectedness of these relations vanishes when it is realised that a piece of completely dried wood contains, in addition to air and insignificant amounts of various substances, wood-substance the specific gravity of which is approximately (or truly?) the same in all kinds of woods. Two pieces of dry wood of the same volume thus differ in weight nearly solely because one contains more woodsubstance than the other. Wood is not a material, but is a heterogeneous and varied structure, and its particular mechanical properties are dependent not merely on the amount of wood-substance contained in its unit of volume, but also on the manner in which that substance is excavated in the form of strong fibres, weak vessels, and so forth. The arrangement, form, and numbers of these

constituents vary widely in different kinds of timbers, with the result that these display corresponding differences in their mechanical proper

ties.

In view of Prof. Record's botanical work on the structure of the woods of the United States, it might have been anticipated that the book under review would deal considerably with the interesting, and incompletely investigated, problems concerning the correlation between the structure and properties of timbers. Very different, however, are the scope and contents of the book, the subject matter of which includes, in order, a brief account of the elementary mechanics of materials, a special consideration of the mechanical properties of wood and of the factors influencing them, and a description of the methods of wood-testing officially adopted in the United States. It gives concise information as to facts gleaned particularly in that country from experiments conducted along the lines laid down by workers in Austria, Germany, and Switzerland; and the information is illustrated by well-chosen figures, including photographs.

The book, however, is akin to a collection of lecture notes dealing with actual experimental results obtained, rather than to a reasoned exposition of the subject. The resultant curtailment is consequently apt at times to lead the student into lack of comprehension or to misconception. The latter is the case when two definitions of hardness are given, the second being "resistance to abrasion or scratching." The truth is that when measured by abrasion the resultant estimates of hardness agree with those obtained by indentation tests and everyday experience with a saw; whereas when tested by scratching all woods are approximately of the same degree of hardness, and that degree is a low one (about equal to muscovite). One feature that takes from the value of the book to English students is that in it, as unfortunately in an increasing number of American scientific books, the language, terminology, and nomenclature are partly foreign to England. Not only are the timbers mentioned exclusively under American names, but popular technical terms unknown in this country are employed, and scientific definitions do not at times accord with those in use here. For instance, a unit stress is defined as "the stress on a unit of sectional area." (Not thus explicable is the erroneous statement on the same page that a "stress-strain diagram" is “a diagram or curve plotted with the increments of load or stress as ordinates, and the increments of strain as abscissæ"; the curve in question supplied shows that the words "increments of " should be omitted.)

In addition to the well-illustrated account of the methods of wood-testing adopted by the U.S. Forest Service, a useful bibliography of the subject, and particularly a list of less-known American papers, gives value to the book. P. G.

WATER REPTILES.

Water Reptiles of the Past and Present. By Prof. S. W. Williston. Pp. vii+251. (Chicago: University of Chicago Press; London: Cambridge University Press, n.d.) Price

125. net.

UST as it is clear that the existing whales and

porpoises are descended from quadrupeds which formerly lived on land, it is gradually being recognised that the marine reptiles which occupied their place during the Secondary Period of geological time also had land-ancestors. Many of the connecting links can now be traced among the fossils discovered during recent years, and so much progress has been made in interpreting them that it is interesting to pause and survey the result. The original papers are scattered through special journals, some of them not easily accessible, and it is necessary to collect the essential facts from numerous sources. We therefore welcome the small book by Prof. Samuel W. Williston, who has devoted many years to the successful study of these reptiles and now reviews the subject exhaustively with first-hand knowledge.

Though the work is mainly suited for students who have some preliminary acquaintance with vertebrate palæontology, Prof. Williston hopes to attract more general readers by a series of introductory chapters dealing with a few elementary geological considerations, and with the structure of the reptilian skeleton and its various modifications in those animals which are adapted for life in water. He then treats the groups of water reptiles in systematic order, referring to the few that survive as well as the great tribes of extinct forms. The descriptions are illustrated both by drawings of the skeletal remains themselves and by many spirited restorations, some original and others by well-known authorities. The technical accounts of structure, indeed, are followed in all cases by a discussion of the inferences they suggest as to the habits and mode of life of the animals in question. All the chapters are well up-to-date, and that on the Cretaceous Mosasauria is especially interesting from its intimate connection with the author's own researches.

As we turn over the pages of this book we are led to speculate as to why nearly all these groups

of water reptiles, so widely distributed in every sea, suddenly became extinct at the end of the Secondary Period, without coming in contact with the whales and porpoises which in later times took their place. Prof. Williston can only suggest that the races may have become effete and died of old age. It is evident that the mystery still awaits solution. A. S. W.

MIND AND MATTER.

(1) The Master-Key: a New Philosophy. By D. Blair. Pp. 118. (Wimbledon : Ashrama Agency, 1914.) Price 3s. 6d. net.

(2) Essays on the Life and Work of Newton. By A. de Morgan, edited by P. E. B. Jourdain. Pp. xiii+ 198. (Chicago and London: The Open Court Publishing Co., 1914.) Price 5s. net. (3) The Analysis of Sensations and the Relation of the Physical to the Psychical. By Dr. E. Mach. Translated by C. M. Williams. Pp. xv+380. (Chicago and London: The Open Court Publishing Co., 1914.) Price 6s. 6d. net. (4) Proceedings of the Aristotelian Society. New series, vol. xiv. Pp. 438. (London: Williams and Norgate, 1914.) Price 10s. 6d. net.

(5) The Philosophy of Change: a Study of the Fundamental Principle of the Philosophy of Bergson. By Dr. H. W. Carr. Pp. xii +216. (London: Macmillan and Co., Ltd., 1914.) Price 6s. net.

(1) THE

HE writer condemns himself by his own pretensions. He calls his system a "new philosophy," and is writing another book"The Truth about the Other World"—which "will be the first genuine Revelation ever published." In the volume under notice he discusses all things in heaven and earth, from the solar spectrum, heredity, and space, to Platonism, hallucinations, and Vedanta. There is evidence of a great deal of heterogeneous and elementary knowledge, but all is confused and superficial. Apparently the author finds salvation in the word Monad-though he does not expound Leibniz— but his explanations do not explain much. posits a "nerve-ether" which is quite different from the luminiferous æther, which latter is "no use" to him; and he seems to have a very poor opinion of the Royal Society. No doubt the society will survive.

He

(2) These reprinted essays, written more than half-a-century ago, are still worth reading, both for their matter and their style. De Morgan was an able mathematician, he made careful researches into the details of Newton's life and controversies, and he had a very characteristic wit. His treatment of Newton is respectful yet critical.

Sir

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