SECONDARY UNDULATIONS OP OCEANIC TIDES. 19 



Bay, situated near its mouth. The secondary undulation is 

 conspicuous and fairly regular ; observed periods are 46.7", 

 51.1-54.0"', and 58.3"-60.0™ ; while the calculated is 48.9". 



(6) Hakodate (July 21-Aug. 10). Top. 8. PI. II, Fig. 4-5 ; 

 PI. III. 



Hakodate is the best anchorage in Hokkaido, situated on 

 the middle coast of the Strait of Tsugaru, which separates 

 Hokkaido from Honshiu. The bay is approximately of a semi- 

 circular shape ; here Kelvin's tide-gauge has been continuously 

 working during the last 20 years, and has recorded several 

 important waves accompanying the sea waves originated along 

 the coasts of Pacific. Our observations Avere chiefly made at 

 the innermost parts of the bay ; i.e. near the wharf of Hakodate. 

 The simultaneous observations between Hakodate and Kamiiso on 

 the opposite sides of the bay, or Hakodate and Tachimachizaki, 

 just inside and outside the bay respectively, were also carried out. 



At Hakodate, the secondary undulation is very conspicuous, 

 sometimes exceeding 30 cm. and fairly regular. The periods of 

 the most conspicuous undulation range from 45.5" to 57.5". 

 Sometimes its octave 21.9"- 24.5" is found superposed on the un- 

 dulation of the above period. In the undulation accompanying 

 the sea waves, the octave always appears in a very marked 

 degree. The longer period was found to correspond to the fun- 

 damental oscillation of the bay, wMle its octave corresponds to 

 its lateral oscillation. 



The calculated periods for these oscillations give 45.3" and 

 23.6" respectively. As we shall see hereafter, the periods of 

 oscillations corresponding to these modes, as given by our model 

 of the bay, are 47.0" and 23.6" respectively. 



When the simultaneous observations between Hakodate and 



