68 K. HONDA, Ï. TERADA, Y. YOSHIDA, AND D. ISITANI. 



the total volume of the water in a bay to the area of the sur- 

 face. The length of the bay was measured along a median 

 line drawn parallel to what was considered to bo the main 

 stream line. 



To find the mean depth of a bay, we began wibh drawing 

 contours on the chart in which the depths at a number of 

 points in the bay referred to low water springs are given. After 

 drawing as many contours as the case requires, we measure by 

 a planimeter areas bounded by successive pairs of contours. 

 These areas multiplied by the corresponding depths, increased 

 if necessary, by the half range, give the partial volumes of 

 water. Dividing the sum of these partial volumes by the area 

 of the free surface, we get the mean depth. 



We calculated by formula (1) the period for all observed 

 bays, and also for those not yet observed, whicJi seem to 

 have the forms specially favourable for oscillation. For several 

 typical bays, w^e also calculated the correction due to the change 

 of the section as well as that due to the mouth, and compared 

 the corrected values with the observed. The calculation was 

 carried out in the following way. 



(a) Bay of Aomori. 



According to our investigation, the Bay of Aomori oscillates 

 in two different modes, that is, the lateral and the longitudinal 

 oscillation with the periods 103'" and 295'" respectively. Con- 

 sidering the bay as a rectangular tank, wdiose length is 55.3 

 km. and whose mean depth is 36.5 ra., w^e get 9 7. 5"' as the period 

 of the oscillation. 



In order to obtain the correction due to the variation of the 

 section, we draw on tlie chart several lines at suitable positions 



