34 K. HONDA, T. TERADA, Y. YOSHIDA, AND D. ISITANI. 



tide at Iwaya is sometimes accelerated and sometimes retarded 

 by several tens of minntes. The tidal Avave in the bay chiefly 

 enters throngh Yuraseto ; but the Harimanada component, which 

 enters through Akashiseto, is easily to be traced. 



As regards the secondary undulations, the longest waves 

 found in the records, have periods of 2 GO" -310'"; the amplitude 

 exceeded ten cm. in one case, (PI. XXII, Fig. 1-3). The 

 phase of oscillations for the four stations, is the same, so 

 tliat this undulation is probably due to the oscillation of the 

 whole basin as a bay witli its narrow necks at Akashiseto and 

 Yuraseto. The result of calculation of the period for the mode 

 of oscillation gives 270™, which agrees well with the observed 

 value. Along with the long wave, one with the period of ca. 

 100" -140"' is often recognized ; the pliase of this undulation is 

 generally the same for the northern statious Iwaya, Imazu and 

 Kishiwada, while for Yura at the southern end of the bay, it 

 is apparently opposite, in so far as we may judge from the 

 faint traces of this component. It is possible that under favour- 

 able conditions, this undulation may become very prominent, 

 though in tlie records at hand, it is scarcely to be detected. 

 Tlie undulation is probably due to the uninodal seiches of the 

 bay along its longer axis. The calculated period of 120" for 

 the suspected seiches is in good agreement with the observed 

 period. Besides, conspicuous undulations with the period of 

 50"- G 5'" are often recognized. Comparing the phases of the 

 undulation at different stations, it is at once found that for 

 Kishiwada and Imazu, the motion is always opposite, and 

 also tliat tlie phase of Yura is the same as that of Imazu. 

 The undulation is probably that of the binodal seiches of 

 tlie bay between Imazu and Yura. The calculated period of 



