December. 1911. 



KNOWLEDGE. 



487 



psjxho-physical problem, the problem of the relation 

 between body and mind." Its anthor has clearly done his 

 utmost to present his material " in a manner not too dry and 

 technical for the general reader who is prepared to grapple 

 with a difficult subject." and truly the subject is a difficult one. 

 Nevertheless, the writer must be warmly congratulated on his 

 bold attempt to make clear that which is to most so obscure, 

 for the definite line of argument which pervades the whole 

 book will make it difficult for any reader who systematically 

 studies it to miss the author's meaning on any one of its 

 closely covered pages. The book is a book for students, 

 amateur and professional, and may be described as a scientific 

 defence of Animism, the theory of the existence of the soul. 

 The author clearly shows that there is no alternative between 

 .Animism and the most absolute Materialism, and boldly stands 

 for the foi-mer ; indeed the present volume is perhaps the first 

 really scientific attempt to justify the soul theory. But it is 

 nuich more than this, for the first half at least is occupied 

 with a " survey of modern theories of the psycho-physical 

 relation," and without this the reasoning of the later chapters 

 is almost impossible to follow. 



The book is clear and concise and excellently written, and 

 though wholly unsuited to the casual reader is most 

 emphatically to be recommended to anyone of average 

 intelligence, who has made up his mind to systematically 

 grapple with this difficult but interesting subject. 



PHYSICS. 



Trctitise on Practical Light. — By Reginald S. Clay. 

 519 pages. 408 illustrations. S-in. X 5-' -in. 



(Macmillan & Co. Price 10 6 net.) 



Dr. Clay's treatise which is an enlargement of his well- 

 known " Practical Exercises in Light," is a book which will 

 be welcome to many. There are many books which deal with 

 optics from a theoretical point of view, from a geometrical 

 standpoint er as an entertaining subject for the lecturer. 

 There has long been required a book which collects together 

 the various methods of optical measurement. Works on 

 Practical Physics contain sundry optical measurements, but 

 seldom can one find just that process of measurement that 

 one requires. Dr. Clay in his introduction says, " There 

 can be no doubt that it is to the advantage of the 

 optical industry both that the difficulties manufacturers 

 find should be known to those whose scientific training may 

 assist in their solution, and also that the experimental methods 

 which have been adopted by individual manufacturers should 

 be known to each other, as well as to those whose interest may 

 be chiefly theoretical. The chapters on aberration of lenses 

 and mirrors and on the compound lens illustrate the above 

 statement, and show that the author has written a book which 

 comes up to these excellent ideals. 



The book commences with a chapter on simple pin experi- 

 ments — some most useful, such as the determination of the 

 angle of the surfaces of a piece of nearly parallel glass, and 

 all very instructive to the beginner. This leads up to a chap- 

 ter on the position and nature of images formed by mirrors 

 and lenses, dealt with in a simple manner ; and then more 

 completely in a chapter on the focal length of lenses and 

 mirrors which contains many \aluable methods and even 

 means of obtaining the radius of curvature of very small 

 lenses as used for microscope objectives. Chapters follow on 

 optical instruments, deviation and dispersion of light, the 

 velocity of light, and focal lines. The adjustments of the 

 spectrometer are well described ; it is such descriptions that 

 make a practical treatise of good value, and it would have 

 been pleasing to have found a rather fuller account of the 

 method of working refractometers, spectrophotometers, and 

 other refined optical appliances. The author's admirable love 

 of simplicity causes him to omitfullerdescriptions of instruments 

 such as the echelon grating spectrometer, and various inter- 

 ferometers and refractometers, and perhaps this is to be 

 regretted, since the research chemist has sometimes to use 

 such instruments and is often rather ignorant of the correct 



method of manipulation, and requires some handbook 'to guide 

 him. However, the chapters on interferometers, diffraction, 

 colours of thin and thick plates and polarised light will be 

 most useful to the student of optics, who has hitherto 

 had to search in man\- different volumes to find the many 

 different instructive experiments the anthor has collected in 

 these chapters. The chapters on vision, colour measurement, 

 resolving power, the compound lens, and the microscope are 

 thoroughly up to date, and contain a great deal of very useful 

 information, useful both to the student and to the technician. 

 It remains to say that the printing, figures and general 

 arrangement of the book are excellent. A r r F 



Principles of Physics. — By William F. Magie. Ph.D. 

 570 pages. 281 illustrations. 9-in.X 5|l-in. 



(G. Bell & Sons. Price 7,6 net.l 



The author mentions in the preface that Physics is the one 

 science of all others in which scientific reasoning is illustrated 

 by the simplest and most varied examples. The peculiar 

 advantages of the science as a means of intellectual training 

 are not given sufficient attention, as physics is now commonly 

 taught ; and the author has endeavoured to present the 

 subject in such a way as to direct attention particularly to 

 the development of its various branches and thus to exemplify 

 the processes of thought which are employed in the examina- 

 tion of a .group of physical phenomena and the establish- 

 ment of a physical law or theory. The book is consequently 

 constructed upon the historical outline. 



The result is an interesting survey of the science of physics, 

 cramped in certain sections of the book a little too much, e.g., 

 electricity, but nevertheless a book useful both to the elemen- 

 tary student and especially to the man who requires a general 

 outlook on Natural Philosophy without having to call to his 

 aid his mathematical facilities, or to bother his memory with 

 a host of details which must be included in any book on 

 Physics which includes the numerous practical applications 

 of the Principles of Physics. The author avoids complication 

 by rigorously keeping only the main principles of the science, 

 and b\' excluding many side issues, e.g., dynamo-electric 

 machinery, steam engines, and so on. \ C C V 



An E.yperiinental Course of Physical Chemistry. — Part I.: 



Statical Experiments. — By James F. Spencer, D.Sc, Ph.D. 



228 pages. 65 illustrations. 7J-in. X4j-in. 



(G. Bell & Sons. Price 3/6.) 



This work, says the author, has been written to provide the 

 student of Physical Chemistry with a guide which shall enable 

 him to carry out for himself the simple physiochemical 

 operations. Dr. Spencer commences well with a chapter on 

 errors and interpretation of results, and continues with a valu- 

 able chapter on the calibration of instruments, weights, measur- 

 ing vessels, and thermometers, another on constant temperature 

 baths, and on the manipulation of gases. These chapters are 

 the most important part of the book, for knowledge of how to 

 work accurately, and consequently of how to calibrate one's 

 instruments, is all important to the physical chemist. When 

 once apparatus is properly set up and its errors determined, 

 accurate measurements are not difficult. Some account of 

 the setting up of cathetometers, and reading microscopes and 

 the calibration of fine capillary tubes might, with advantage, 

 have been included. 



The rest of the book deals with the determinations of 

 various physical constants, and the descriptions are very clear 

 and concise. Density, atomicity, molecular weights, solubility, 

 viscosity, surface tension, polarimetry. spectroscopy, refrac- 

 tivity. and thermal measurements are dealt with in succession. 

 -A useful collection of tables is to be found at the end of this 

 well got up and useful book. The student of physical 

 chemistry will find most of what he wants in this small book 

 and can always refer for greater detail to Ostwald and Luther's 

 '■ Physiko-chemische Messungen " ; the one is a laboratory 

 working guide, the other a reference book, .\nother volume 

 of dynamical experiments is to follow this volume shortlv. 



.A. C. G. E. 



