16 • K. HONDA, T. TERÂDA, Y. YOSHmA, AND D. ISITANI. 



In a bay, beside the uninoclal oscillation above referred to, 

 the oscillations with two nodes, three nodes etc., are equally 

 possible ; the periods of these oscillations are respectively h i 

 etc. of the period of the fundamental oscillation. In some 

 cases, the lateral oscillation of tlie bay excited by incident 

 waves is also possible, the period of which is principally deter- 

 mined by the oscillating water in the bay. These modes of 

 oscillations were actually found to exist in some bays such as 

 Hososhima, Ofunato, and Hakodate. 



In the oscillation of the bay water just referred to, the 

 period of the forcing wave which corresponds to the maximum 

 resonance is not sharply defined ; l^ut within a certain range of 

 the period, the oscillation remains fairly conspicuous, as we 

 have often observed. 



In bays of regular shape, such as Ofunato and Hososhima, 

 the position of the nodal line is determinate ; but in bays of 

 complicated shape, such as Shimoda and Susaki, several nodal 

 lines are conceivable. By the choice of the nodal lines, the 

 length and mean depth of the bay vary within a considerable 

 range, so that the period of the proper oscillation changes within 

 a certain range. Hence such a bay may resonate to any one 

 of the incident waves with the period lying within the same 

 range. In the two bays above mentioned, the period of the 

 conspicuous undulation was actually found to vary within a 

 moderately wide range. 



As to the cause of the long waves, which manifest them- 

 selves as secondary undulations, we may mention the wind, the 

 cyclone, the earthquake, etc. It is a matter of fact that the 

 seiches in many lakes, which are the result of interference of 

 a direct and a reflected wave of long wave-length, are often 



