MODERN SEISMOLOGY^ 



By F. J. ScKASB 

 Kew Observatory 



INTRODUCTION 



As the main branches of science expand and overlap each other, 

 new subdivisions become recognized. Geophysics is a conspicuous 

 instance of such subdivision, and it is one in which there has be<?n 

 a considerable development of interest in recent years. In view 

 of this development the National Research Council at Washington 

 has thought it desirable to prepare a series of bulletins on the 

 physics of the earth with the object of giving scientists who have 

 no special knowledge of the subject some idea of the present position 

 of geophysics and its main problems. Several bulletins of this 

 series have already appeared, the most recent being one on seis- 

 mology.* The authors of this volume, viz, J. B. Macelwane, H. O. 

 Wood, H. F. Reid, J. A. Anderson, and P. Byerly, are all well-known 

 seismologists, and their symposium forms a clear and compre- 

 hensive survey, mainly from the physical standpoint, of modern ideas 

 on the subject. In the present article it is not intended to give 

 more than a brief outline of these ideas; those readers who feel 

 encouraged to enter more deeply into the subject will find the 

 National Research Council's bulletin a useful guide to further study 

 of the physics of earthquakes. 



THE GROWTH OF MODERN SEISMOLOGY 



Before the latter part of the last century seismology did not 

 offer a very attractive field to scientific men, mainly because the 

 data then available were crude and unreliable. That the subject 

 has now taken its place as a quantitative physical science is due, 

 in no small measure, to the pioneer work of John Milne, whose 



^ Reprinted by jHTinission, with slight alterations, from Science Progress, no. ll.*?, 

 July 1934, published by Edward Arnold & Co., London. 



* Bulletin of the National Research Council, no. 90. 'Physics of the Earth, vol. 6 ; 

 Seismology. Pp. viil + 233 (Washington, D. C. : National Academy of Sciences, 1933). 

 Paper, $2; cloth, $2.50. 



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