SECONDARY UNDULATIONS OF OCEANIC TIDES. 53 



them. The periods of these oscillations were 3.27' and 1.64' 

 respectively ; multiplying by r, we get 47.0"' and 23.6™ in good 

 coincidence with the observed values. These tw^o modes of 

 oscillation are clearly seen from the photographs No. 1 and 2. 

 Though the photographs show beautifully the line of motion of 

 the water particles, they do not give the direction of motion ; 

 hence in Fig. 1 and 2 the direction of motion, as actually observed 

 by experiments, is indicated by arrow^s. It is very interesting to 

 trace the stream lines in the case of the lateral oscillation (Fig. 

 2). Certain stream lines extend from Hakodate to Tomikawa 

 and gradually diverge toward the middle, while other lines run 

 toward the mouth of the bay from the Tomikawa side. 



In experimenting with models, it was observed that the 

 period of the forcing wave, which corresponds to the maximum 

 resonance, is not well defined ; wdthin a certain range of the 

 period, wliich did not much differ from the period of free oscil- 

 lation, the oscillation remained fairly conspicuous. 



In the actual bay, such a phenomenon was also observed : 

 conspicuous undulations of 45.5"-57.5"' were frequently observed, 

 the period of free oscillation of the bay being 47.0"'. 



(6) Bay of Aomori. PI. LXXXVIII. 



The scales of the model w^ere as foUow^s : — Length 1 : 

 110,700, and depth 1 : 731, so that the factor v w^as 4,090. 



The model had also two modes of oscillation as in the case 

 of Hakodate, i.e. the fundamental and the lateral oscillation. The 

 periods of their free oscillations were 4.45' and 1.60' respective- 

 ly ; multiplying by r, we get 303"" and 108"\ During our ob- 

 servations on the actual bay, two oscillations of the periods 

 300™ and 103™ were observed, which well accord with the above 



