REVIEWS 



The Physics of Earthquake Phenomena. By Cargill Gilston Knott, D.Sc, 

 F.R.S.E. [Octavo, pp. xii. + 283.] (Oxford: At the Clarendon Press, 

 1908. 14J. net.) 



The author has several qualifications for his task. During eight years he was 

 Professor of Physics at Tokyo in the Imperial University of Japan, which gave 

 him a first-hand knowledge of the practical side of earthquakes. While resident 

 in Japan, and subsequently, he has made earthquake phenomena the subject of 

 several original researches. Finally, so far as we know, he has not invented a 

 seismograph. His aim, as is mentioned in the preface, is not to give a complete 

 account of all earthquake phenomena, but merely of such as are intimately 

 connected with physical theory. The nature of the work was presumably deter- 

 mined to a considerable extent by the fact that it is the outcome of " Thomson 

 Lectures " delivered in Aberdeen in 1905-6. The audience, though hardly to be 

 described as popular, was not one deeply versed in physical science, and minute 

 details of mathematical investigations would have been out of place. This pre- 

 sumably explains why there is comparatively little mathematics in the book, 

 though it refers to a variety of subjects requiring advanced mathematics for their 

 complete presentation. Those who wish fuller mathematical treatment will have 

 to go elsewhere. At the same time, they will obtain a clearer idea of the true 

 nature of the problems presented, and of the difficulties remaining to be sur- 

 mounted, than is obtainable from any previous book published in England. 



After a brief survey of earthquake phenomena, the author discusses the 

 amplitudes of the earth movements produced, and how the energy of the shock 

 varies with the distance from the epicentre. Following a short description of the 

 Milne, Omori, and some other forms of seismograph, there is a discussion of the 

 fundamentally important problem of forced vibrations and resonance effects in 

 the pendulums which form the essential part of most seismographs. Special 

 consideration is given to the recent work of Galitzin, which deserves to be better 

 known than it is in this country. 



A short chapter, based mainly on Milne's work, is devoted to the geographical 

 distribution of earthquake origins. The question of the supposed periodicities — 

 daily, lunar, annual— in the frequency of earthquakes is discussed in considerable 

 detail in two chapters. The author makes use of Schuster's criteria in deciding 

 as to the reality of the various periodicities, and adopts a distinctly critical 

 attitude. Thirty pages are devoted to some aspects of the mathematical theory 

 of elasticity, auxiliary to the study of the propagation of earthquake waves, and 

 to the reflection and refraction of waves at a plane surface separating two different 

 media. Two long chapters deal with seismic records — various specimens of which 

 are reproduced — and with the nature and velocity of the different types of waves 

 to which different portions of each earthquake record are due. The last chapter 

 relates to a number of disconnected problems, including Milne's investigation into 

 the supposed connection between the frequency of large earthquakes and the 

 small movements of the earth's axis. 



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