82 K. nONDA, T. TER ADA, Y. YOSHIDA, AND D. ISITANI. 



in the above table being the mean vakies of several oscillations 

 in comparatively regular trains and therefore the period of 

 single undulation may differ from the mean In^ a few minutes. 

 At San Francisco, the waves of about 41"' appeared most fre- 

 quently, though the period SS"' of Shimoda wave also manifested 

 itself. By referring to the result of experiment with models, 

 it may be noted tliat these periods probably correspond to the 

 higher modes of oscillation of the bay. At San Diego, the 

 period 31™- 3 5"" appeared most conspicuously, which probably 

 corresponds to trinodal seiches of the bay. It is a characteristic 

 feature of this sea wave that at these stations, the initial waves 

 are not conspicuous and their amplitudes gradually increase. 



The mean velocity of propagation of the Avave from South 

 America to Astoria, San Francisco or San Diego can be cal- 

 culated, if the path through which the wave actually travelled 

 be known ; but this is not an easy matter, the condition of the 

 bottom along the coast line of America being complex. 



In Japan, the wave was observed at Hakodate by Captain 

 T. Blakiston, who wrote the following passage to Professor 

 Milne : — 



"On August 15, at 10'' 30"" a.m., a series of bores or tidal 

 waves commenced, and lasted until 3'' p.m. In ten minutes, 

 there was a difference in the sea level of 10 feet, the water 

 rising above high water and falling below low water mark with 

 greater rapidity." 



Now the periods of the ordinary conspicuous undulation in 

 the Bay of Hakodate are éS'-oT" and 22'"-24". In the case of 

 sea waves, the latter period always appears superposed on the 

 former. According to the report of tlie captain, half the period 

 of the present sea wave is 1 0™ ; allowing errors of 1 or 2 minutes 



