78 K. HONDA, T. TEßADA, Y. YOSHIDA, AND D. ISITANI. 



seem to indicate that the periods of the sea waves did not 

 coincide with those observed in ordinary cases. 



In the investigation of the nature of sea waves, the tide- 

 gauge is the only instrument available at present ; but for this 

 purpose, it is necessary to set up the instrument on an open 

 coast, or better on a small isolated island, and not in a bay, 

 where the waves are much modified by the oscillation proper 

 thereto. 



In the following pages, discussions regarding to several sea 

 waves in the light of our present investigation will be given. 



(a) Sea waves of Ansei, 1854. 



The destructive sea waves of 1854, which accompanied the 

 great earthquake of Ansei, devastated the great part of our 

 Pacific coast, and were felt by the tide-gauges at San Francisco 

 and San Diego. 



On December 23, at 9'' 15" a.m., a strong shock was felt at 

 Shimoda in Izu ; at 10", it was followed by a large wave 9 m. in 

 height. The rising and falling of the water continued several 

 hours ; in all, there were six large waves, the period of which 

 seems to have been 15"-20"\ if we judge from the descriptions 

 by a suflferer. The period is the same as that usually observed 

 in the bay. A Russian man-of-war then at anchor, was de- 

 stroyed by the waves. 



At Tanabe in Ivii, seven or eight waves were observed from 

 the morning to the evening ; at Nagashima in the same province, 

 the first wave was the highest, after which two weak waves 

 were counted. At Toba in Shima, the first and fourth waves 

 are said to have been tlie highest. An irregularity of tides was 

 also observed in Tosa ; at Kôchi, three ebb-and-flows were counted 

 from 9'' a.m. to 2" p.m. 



