472 Revieics — Seismology in Japan. 



of Horizontal Pendulums, pp. 35-54. (4) J. Milne: A Note on Horizontal 

 Pendulums, pp. 55-60. (5) H. Darwin : A Bifilar Pendulum, pp. 61-63. (6) J. 

 Milne : A Note on Earth. Pulsations and Mine Gas, pp. 65-69. (7) P. Omori : 

 On After -Shocks, pp. 71-80. (8) E. J. Pereira: Eecord of Yokohama Earth- 

 quakes, 1890-1894, pp. 81-86. (9) J. Milne: Velocities of the Earth Waves, 

 pp. 87-89. (10) M. Daubree: La Cause des Tremblements de Terre, pp. 91-106. 



The increasing attention paid to the study of earth-pulsations is 

 strikingly shown in this new volume. Five out of the ten papers 

 are indeed more or less connected with the subject. Prof. Milne (4) 

 describes a modification of his conical pendulum, one of the least 

 expensive instruments used for their investigatioQ. Dr. von Rebeur- 

 Paschwitz (3), who has done so much excellent work with the 

 horizontal pendulum, gives many practical details of the greatest 

 service to those engaged, or about to engage, in this fascinating study. 



In the other papers, Mi*. P. Omori (1) describes the eruption of 

 Azuma-san in 1893, and proves that the conical holes surrounding 

 the crater were produced by falling stones. Professor Milne (2) 

 concludes that we do not yet possess any certain evidence of a 

 physical connection between earthquakes and electric and magnetic 

 phenomena. Mr. Pereira continues his useful list of Yokohama 

 shocks. 



Mr. F. Omori (7) discusses the relative frequency of the after- 

 shocks of the great earthquakes of Kumamoto in 1889, Mino-Owari 

 in 1891, and Kagoshima in 1893. Every strong earthquake is 

 invariably followed by a few weaker shocks ; a destructive earth- 

 quake may be succeeded by even hundreds or thousands. For 

 instance, during the two years after the Mino-Owari earthquake, as 

 many as 3364 after-shocks were recorded at the Gifu meteorological 

 station. Of these, 11 were violent, 97 strong, 1809 weak, 1039 

 slight, and the remaining 408 merely sounds. Ten of the violent 

 shocks occurred during the first four months, the strong shocks all 

 within the first thirteen months, and the weak ones all within the 

 first twenty months. Towards the end only slight shocks and 

 sounds were observed. Curves are drawn showing how the after- 

 shocks gradually became less frequent. Eoughly rectangular 

 hyperbolas, they at the same time exhibit several maxima and 

 minima, corresponding to pei'iodic fluctuations in seismic frequency. 

 Mr. Omori reckons that after a lapse of about ten years, the residual 

 effect of the Mino-Owari earthquake will be so far reduced that 

 thei'e will be only one weak shock a month. 



Lastly, M. Daubree (10), noting the usual classification of earth- 

 quakes into volcanic (due primarily to the action of steam) and 

 non- volcanic (connected with fractures in the earth's crust), and 

 referring to the frequent occurrence of after-shocks, endeavours to 

 trace both classes to the same origin. " Les tremblements de terre 

 des regions depourvues de volcans," he concludes, " paraissent dus 

 aux effets d'un sorte d'eruption volcanique qui ne pent aboutir 

 jusqu'a la surface, et semblent dependre, aussi bien que ceux des 

 regions volcaniques, d'une cause unique : la vapeur d'eau, animee 

 de la puissance enorme qu'elle acquiert dans les profondeurs de la 

 croiite terrestre." C. Davison. 



