288 T. Terapa and T. Mattjzawa 



to these effects. According to his results, not only the islands, Init 

 also most of the inland volcanoes give large correlation coefficients 

 above 0.7, with respect to the tidal pressure, while the correlation with 

 the barometric pressure, though quite sensible for most of the volcanoes 

 on the central zone of Honsyu, yet is not so cons})icuous as in the case 

 of tidal pressure. Mt. Asama turned out an exception to his results. 

 His results generally' confirm Omori's, but he remarks that volcanoes 

 situated near the coast decline in activity when the barometric pres- 

 sure decreases. 



Recently T. Isikawa^'- remarked that a volcanic eruption is apt 

 to occur when the mountain lies in the midst of an anticyclonic area. 



The correlation between the different volcanoes,'-^ as well as that 

 between earthquakes and volcanic eruptions have been investigated by 

 Omori.^"^ S. Ono'"*^ recently alluded to the laiter subject in connection 

 with his original research on the isostatic block structure of the land. 

 Though it seems quite certain that such relations exist, the time has 

 j)erhaps not yet come when we may state anything very definite on 

 this matter. 



Mathematical and Physical Investigations. 



The development of seism ometry has brought to light many 

 interesting characteristics of earthquake phenomena which furnish a 

 number of problems concerning the mathematical theory of elasticity. 

 In the earliest days, C. G. Knott^''^^ treated of the reflection and refrac- 

 tion of elastic waves at the boundary between two different media. 

 As a special case he considered the refraction into air, for explaining 

 tlie origin of the earth sound. Introducing the ideas of purely elastic 

 and quasi-elastic vibrations, he identified the principal portion of 

 earthquake motions to the latter and the preliminary part to the 

 former. 



A somewhat similar idea was adopted later by S. Kusakabe.^"^ 



(1) J.M.S., [ii] 3 (1925), 255, e. 



(2) Bull., 6, No. 1 (1912) ; 8, No. 2 (1922). 



(3) Ho.. 43 (190,3); 67 (1910) ; Bull., 2, No. 2 (1908); S, No. 1 (1911); 8, No. 6 

 (1922) Also, T. Ogawa, Mem. Kyo., B. 1, No. 2, Art. 2 (1924). 



(4) Kensinzibo, 1 (1926) 221. 



(5) Trans. Seism. Soc. Jap., 12 (1888). 



(6) Pub. 14 (1903); 17 (1904); T.S.B.K., 1 (1902), 103; 2 (1904), 142, 197; 2 

 (1905), 341 ; 3 (1906), 110. 



