DEVELOPMENT OE SEISMOLOGY [N JAPAN 279 



Hongo, at Komaba in the suburbs of the city, and ai. Mitakamura 

 The relative amplitudes were found to be 1; 1/3 and 1/10 respectively. 

 In this connexion, the recent theoretical investigation of Matuzawa^^^ 

 into the possible gravitational Wiives in the superficial soil layer may 

 be referred to. 



Omori's*^-^ extensive studies on microseisms at Asama Volcano is 

 noteworthy. He found that the tremors consist of two distinct classes : 

 one is a train of rapid vibrations not accompanied by any eruption 

 of the volcano, while the other begins with slow oscillations and is 

 followed after a few seconds by rapid vibrations usually accompanied 

 by an eruption. The former is attributed to the occurrence of a 

 subterranean fissure at a great depth, while the latter is considered 

 to be due to the eruption itself. He also noticed that the first 

 motion of the earth due to the eruption is invariably directed 

 toward the crater. Omori*^'"^ also observed the microseisms on the 

 crater wall of Mihara Volcano, Oosima, and noticed the difference 

 of the periods of vibration for the radial and tangential directions. 



Imamura'^''^ investigated the pulsations which appeared after tlie 

 Anegawa Earthquake of 1909 and was led to the conclusion that the 

 phenomena may be interpreted as the ra])id sequences of slight 

 after-shocks. 



Shida^^^ constructed a highly sensitive baro-variometer, or micro- 

 barograph with which he established the existence of atmospheric 

 waves with periods similar to those of the terrestrial waves observed 

 as pulsations. 



Matuzawa"^^^ recently studied the pulsations observed at Tokyo, 

 According to his results the essential factor of the exciting agency 

 consists in the behaviour of the atmospheric pressure wliile other 

 factors play only trifling roles, if any. The occurrence of two different 

 types of motions as distinguished by Omori, that is, regular and 

 in-egular, can also be explained by the behaviour of the atmospheric 

 jjressure. The comparison of motions at different places reveals that 

 each locality possesses some kind of oscillating system peculiar to it. 



(1) N.S.B.K., [iii] 7 (1915), 88; Jap. J. Astr. Geopliys, 3 (1926.\ 161. 



(2) Ho., 73 (1911); 87 (1918); Bull., 5, No. 3 (1918). 



(3) Ho., 81 (1915). 



(4) Ho., 70 (1910). 



(5) T.a.B.K., 5 (1909), 76. 



(6) Not yet published. 



