292 T. Tkrapa and T. Matttzawa 



light intensity of Nova Aqiiilae and that of tlie frequency of after- 

 shoclvS and remarked that an analogous fluctuation may also be 

 brought forth by mere accident. 



S. Sano^^' treated the problem of the wave produced by normal 

 pressure exerted on the surface of a semi-infinite elastic solid and 

 obtained a mathematical solution l)y applying Fredholm's theorem. 

 No practical application has been made. 



Eecently, H. Nahauo^-' made an important contribution on the 

 problem of the Rayleigh waves. He treats the two-dimensional 

 pro])lem with a free boundary plane, below which a line source of 

 disturbance is situated at a certain depth, parallel to the plane. 

 First, the periodic disturbances of compressional and distortional types 

 are respectively considered and, later, the discussion is extended to the 

 case where the disturlmnce at the source is an arbitrary function of 

 time, by making use of Fourier's integral. According 1o his result, 

 the Eayleigh wave does not appear in the vicinity of the origin, but 

 becomes perceptible only bej'ond a certain distance great in comparison 

 with the depth of the origin and determined by the velocities of 

 waves and the depth. Nearer the origin, the Eayleigh wave a})pears 

 gradually with no marked phase for identifying the beginning of this 

 kind of wave. 



Nakano^^^ also treated the problem of wave propagation in infinite 

 solid due to different kinds of meclianisms of disturbances at the origin 

 consisting of pairs of simple sources, and explained various instances 

 of the distribution of the direction of motion revealed by the actual 

 observations. 



Most recently Matuzawa^'^^ treated a similar problem and applied 

 his results for the explanations of different examples of the anomalous 

 propagation of seismic Avaves, as already njentioned, for instance, the 

 case with no apparent preliminary tremor observed by Omori, the 

 difference in the behaviour of waves propagated in directions perpen- 

 dicular and tangential respectively to the arc of the land, as pointed 

 out by Kunitomi, etc. 



(1) T.S.B.K., 7 (1914), 343. 



(2) Jap. J. Astr. Geopbys., 2 (1925), 233. 



(3) The Seism. Bull, of CM.O., 1 (1923), 92. The paper was printed just before 

 the Great Earthquake and abnost all the copies were destroyed in the conflagra- 

 tion. See for an allied problem also: S. JSTakamnra, J.M.S., 41 (1922), e. 1 ; K.Suda, 

 U.t.S., 5 (1925), 46, 64, 80. 



(4) Jap. J. Astr. Geophys., 4 (1926).! 



