148 



NA TURE 



[June i8, 190S 



The above facts should become known to intending' 

 players, so that they may not be misled into thinking' 

 that they will make their fortunes by following the 

 advice given in M. Henry's book. That book adds 

 nothing to our knowledge of the probabilities con- 

 nected with roulette at Monte Carlo. 



THE THEORY OF LIGHT. 

 The Theory of Light: A Treatise on Physical Optics. 

 By Richard C. .Maclaurin. In three parts. Part i. 

 Pp. viii-l-326. (Cambridge : University Press, 1908.) 

 Price gs. net. 



THIS is the first instalment of a work on optics 

 arranged on a somewhat novel plan. The volume 

 treats mainly of the propagation of light in homogene- 

 ous media, isotropic or crystalline, and of the laws 

 of reflection and refraction at plane boundaries. It is 

 to be followed by a second dealing with the subjects 

 of diffraction, dispersion, aberration, &c. ; whilst a 

 concluding volume is to be devoted to the history of 

 optical theory. The method followed is deductive ; a 

 medium of the McCuUagh type is postulated, and the 

 laws of wave-motion are obtained by an application of 

 the principle of Action. This is practically, of course, 

 the electric theory of light in the form adopted by 

 Larmor. The subsequent developments are naturally 

 almost entirely mathematical, experimental methods 

 being rarely referred to. For this reason the work 

 cannot claim to be, indeed does not profess to 

 be, a complete handbook of the subject ; but this is 

 hardly to be regretted, since the English student 

 already has within his reach two masterly expositions 

 from the physical standpoint in Lord Rayleigh's 

 Encyc. Brit, article, and in Prof. Schuster's 

 " Optics." A more serious matter is that some recent 

 speculations of importance are ignored. For instance, 

 we read on p. 29 : — 



'' The answer forced upon us by the experimental 

 evidence is that we must regard the [components of 

 white] light as polarised elliptically ... for an in- 

 terval of time which is long compared with the period 

 of vibration, but very short compared with the time 

 required to make any impression on the retina or on 

 a photographic plate." 



This brings us back to the standpoint of .Xirv's 

 "Tracts." It is to be hoped that the author will 

 return to this question in his second volume, and that 

 the bearing on it of Rayleigh's and Schuster's work 

 on interference will receive due consideration. 



The real value of the book consists in the systematic 

 mathematical discussion of various classes of 

 phenomena from a common point of view. In par- 

 ticular, many readers will be glad to have in an 

 easily accessible form the author's own investigations 

 of the effect of a thin transition layer in the pheno- 

 mena of ordinary and crystalline reflection and refrac- 

 tion, and metallic reflection. Regard being had to 

 the point of vievi-, the style is clear and attractive, and 

 the reader 'will appreciate the numerous excellent 

 graphical representations of the somewhat complicated 

 theoretical results. 



In a lively introductory chapter the author discusses 

 the methods and aims of science, the object being 

 NO. 20 1 6, VOL. 78] 



apparently to anticipate criticisms which might be 

 directed against the special theoretical basis which 

 he has adopted for his exposition. This discussion is 

 pleasant reading enough, but it is to be hoped that 

 future ■writers on mathematical physics will not always 

 think it necessary to begin in this way. From the 

 student's point of view the procedure has this dis- 

 advantage, that he niay find the introduction much 

 harder than the book, and perhaps even not intelligible 

 until he has read the book. In the present instance 

 the opening sentence tells us that " the first question 

 in the catechism of every physicist " should be " what 

 is the chief end of science? " The author's own reply 

 to tliis question is interesting, and has the present 

 writer's sympathy, but one cannot help wondering what 

 degree of uniforniity would be found among the 

 answers which would have been given by, say, Archi- 

 medes, Galileo, Xewton, Pascal, Laplace, Young, 

 Maxwell, Kelvin. Fortunately history shows that the 

 progress of science is not really conditional on the 

 correct resolution of so formidable a question, any 

 more than art has ever stood still for want of a defini- 

 tive reply to the other secular question, what con- 

 stitutes the Beautiful? 



The remaining volumes will be looked forward to 

 with interest, and the historical section in particular 

 should prove of great value. H. L. 



GEOLOGICAL EPITOMES. 



Die Alpen. By Dr. Fritz Machacek. Pp. iv+146. 



(Leipzig : Quelle and Mayer, 190S.) Price 1.25 



marks. 

 Eiszeit iind Vrgcschichic Jes Mensclicn. Bv Prof. 



Hans Pohlig. Pp. viii-l-142. (Leipzig: Quelle and 



Mayer, 1907.) Price 1.25 marks. 



THESE two books, bound in cloth and convenient 

 for the pocket, are members of Dr. Paul 

 Herre's series entitled " W'issenschaft und Bildung. " 

 They are printed in the older German type, presum- 

 ably to give them a popular and untechnical aspect ; 

 and their cheapness prevents their half-tone illustra- 

 tions from being more than suggestive. But the 

 text is by no means of the " nature-study " order, or 

 merely intended to lead a young reader on to better 

 things; it is rather a summary of the results of a wide 

 range of specialised research. 



Dr. Machacek in his volume compares the views of 

 various authors on the structure of the eastern and 

 the western Alps, and discusses the origin of the pre- 

 sent surface-relief. He accepts the theory of glacial 

 erosion for the " Zungenbecken " of the North Italian 

 lakes as a logical outcome of observations on the 

 deepening of the main glaciated valleys further up 

 among the Alps ; and he attributes the rich variety 

 of pictorial features (p. 56) in the central chain to the 

 denuding activities of the Ice-age. Surely no one can 

 nowadays deny the efficacy of " frost-nibbling " in 

 producing crags and cirques and wild aretes, when 

 combined with the presence of glaciers, which carry 

 off the debris froni the scene of severest action. Nor 

 can the modification in form of the original valleys 

 excavated by streams be ascribed to anything but the 



