56 K. HONDA, T. TERADA, Y. YOSHIDA, AND D. LSITANI. 



also a stream in the direction from Nagasaki to Fukahori, and 

 when the water flows in the opposite direction, there is also a 

 stream directed towards Nagasaki, thus forming an oscillation 

 similar to the seiches between the two places. 



The proper periods corresponding to these two modes of 

 oscillation are 2.68' and 4.45' ; multiplying by r, we get 23.3™ 

 and 38.4™ in good agreement with the observed periods. 



(r/) Bay of San Francisco. PI. XCII. 



During the last fifty years, the tide-gauge at San Francisco 

 has recorded several sea waves which originated at different 

 coasts of the Pacific ; the periods of the waves recorded are 

 17.3'"- 19.2™, 24.3™- 27.8™, 34.3™- 41.2™, 47.4™ and 116™, of which 

 the first is an octave of the third. 



Now the Bay of San Francisco is of a very complicated 

 form, so that it is very difficult to find out by calculation what 

 modes of oscillation correspond to the actual periods. Hence a 

 model of the bay was constructed after the chart published by 

 Washington Coast and Geodetic Survey and presented to Pro- 

 fessor F. Omori by Dr. 0. H. Tittmann, superintendent of the 

 Office. The scales of the model were as follows : — Length 

 1 : 40,000, and depth 1 : 366, so that the factor r was 2,076. 

 The model was too large to be put in the tank and so it w^as 

 placed in a small pond of the University. Since the greater 

 part of the model was very shallow, the oscillation rapidly sub- 

 sided, when the exciting wave was stopped, so that the period 

 was always determined by observing tlie maximum resonance 

 of the bay. For tlie exciting wave incident on Golden Gate, 

 the principal modes of oscillation of the water were the oscil- 

 lations between the West Berkeley and Sausahto sides. The 



