SECONDAKY UNDULATIONS OP OCEANIC TIDES. 29 



110'"-130™ are often traceable. Since the bay is very large and 

 shallow, it can not easily be set in oscillation as a whole by any 

 usual cause of excitement. Judging from the calculated periods 

 222"' and 158'" for the fundamental and the seiches oscillation re- 

 spectively, the observed periods may be the higher harmonics of 

 these oscillations, but considering the smallness of the amplitude 

 of oscillation, they are perhaps rather due to progressive waves. 



In the record at Kanegafuchi, the relation between the rise of 

 the level by a flood and the change of the tidal range deserves notice. 

 As the level of the river increases, the tidal range (PI. XIII, 

 Fig. 4) becomes gradually less and at last very small. As the 

 level gradually falls the tidal undulation is again restored. 



(14) Moroiso. Top. 30. PI. XIV, Fig. 1-5 ; PI. XV, Fig. 1-4. 



About 4 km. north of Misaki, there lies a small branched 

 bay ; the one branch is called Moroiso and the other Abura- 

 tsubo. 



At Aburatsubo, a Kelvin's tide-gauge is constantly working, 

 to the record of which Professor F. Omori has frequently re- 

 ferred as Misaki mareogram. In the spring vacation of 1906, 

 we also made simultaneous observations at different parts of 

 the bay. 



The undulution is very regular and conspicuous, having the 

 periods 13.8™-15.6"' ; the calculation gives a fairly coincident 

 value 13.4"\ 



The record shows an appearance of the beat of two waves 

 of nearly the same wave length. So it was suspected that the 

 phenomenon may be due to the interference of the two distinct 

 modes of oscillation of the two branches of the bay which 

 constitute a vibrating system with two degrees of freedom ; but 

 this is not the case, since the simultaneous observations at 



