14 K. HONDA, T. ÏEEADA, Y. YOSHIDA, AND D. ISITANI. 



tions appear in the same phase with respect to the tidal wave 

 on consecutive clays of ordinary weather. 



9. The phases of the prominent fundamental undulation at 

 different parts of a bay are equal. 



10. The periods T of the most pronounced undulations is 

 fairly given by the relation 



^/g^l 



where / is the length of the bay measured along its depth, h the 

 mean depth of the bay, and g the acceleration due to gravity. 



11. Just outside a bay, the undulation, which appears 

 inside the bay with considerable amplitude, may also be traced, 

 but its amplitude is very small. 



12. In a bay, the periods of the conspicuous undulations 

 in the case of a storm, or a sea wave of distant origin, are the 

 same as those ordinarily observable in the ba}'. 



It has long been believed that the secondary undulation in 

 a bay is the seiches between two opposite sides of the bay, but 

 according to our observations, the phase of the conspicuous 

 undulation is usually the same throughout the bay, so that this 

 view can not be generally true. 



Napier Denison considers the undulation to be long waves 

 propagating from the ocean toward the bay. All results above 

 enumerated, except the 7th, 9th, 10th and 12th, can be ex- 

 plained by his view. But the fact, that there is a prominent 

 undulation peculiar to each bay, can not be explained by merely 

 considering progressive waves. 



The undulation in a bay can, however, be explained in the 

 following way. For the sake of simplicity, take a rectangular 

 bay of a constant depth. Suppose a regular series of long waves 



