SECONDAEY UNDULATIONS OF OCEANIC TIDES. 6 



plurinodal sfoitionary oscillation of the ba}^ and observed that 

 oscillations of conspicuons amplitude occur in connection with 

 barometric disturbances. 



In tlie bays on the Pacific coasts of Japan, the phenomenon 

 is sometimes so conspicuous that it is commonly known as 

 yota. In the liarbour of Nagasaki, it is called the abiki ; its 

 amplitude of oscillation frequently exceeds 50 or 60 cms. The 

 yota or abiki is frequently accompanied with calm weather pre- 

 ceeding low barometric pressure, which is approaching our 

 coasts. 



Professor F. Omori'^' investigated the secondary undulations 

 of Ayukawa, Misaki and Hososhima mareograms in connection 

 with the discussion of the several destructive sea waves, and 

 found that the periods of the waves are the same as those 

 observed in ordinary cases. The records of the tide-gauges 

 on Indian coastsf , of the waves which accompanied the great 

 eruption of Krakatoa, 1883, were also found to show the same 

 periods as frequently occur in ordinary cases. He explained 

 this interesting fact by the consideration that a bay or a certain 

 portion of the sea oscillates like a fluid pendulum with its own 

 period. Professor H. Nagaoka,^ in his paper on the hydrody- 

 namical investigation of the destructive sea waves, expressed 

 the desirability of a special inquiry concerning the phenomenon. 

 The suggestion was taken up by the Earthquake Investigation 

 Committee, and the task of carrying out a systematic observa- 

 tion was imposed upon us. 



The observations were carried out during the period of 1903 



*) Omori, Publications o£ Earthquake Investigation Committee 34, p. 5, 1900. 

 t) Omori, Proc. Tokyo. Math.-Phys. Soc. 2, p. 45.5, 1905. Publications of EartL. Inves. 

 Comm. 56, p. 29, 1906. 



Î) Nagaoka, Proc. Tokyo Math.-Phys. Soc. 1, p. 126, 1903. 



