70 s. Nakamura and K. Honda. 



The e.xperiment conducted with a model in cement gave three 

 different motions with the following periods 



^1=0.90 sec, 



^.=0.50. 



^3=0.39. 

 Their modes of oscillation were photographed and are reproduced 

 in Plate XI. The existence of other motions could not be deter- 

 mined with certainty, as the periods for them were too small. The 

 ratios between these three periods are 



^1:^2:^3=1.00:0.67:0.43 

 From the period ^i=0.90 sec. of the uninodal oscillation of the 

 model, we deduce a period of 15.9 minutes as that of the actual 

 lake. Again as the ratio t^-J.^ is nearly equal to the ratio T^: T^, we 

 may safely conclude tliat Ti = 15.61 minutes is the uninodal 

 longitudinal seiche, and the Tg^ 10.57 minutes is the binodal 

 longitudinal seiche of the lake. With respect to the third 

 motion, the correpondence of 2\ and ^3 is not so good as in the 

 other motions. Tlie photograph of t^ shows that it has a nodal 

 line of nearly circular form, with its concavity turned toward the 

 station of Nagaiké, and another nodal line running across the 

 narrow neck in the northeastern end. The motion is therefore 

 mainly transversal, and we may describe ^3 as the transversal 

 oscillation with a secondary synchronous motion in the neck. If 

 we assume that T^ corresponds to ^3, then the observed motion 

 with a period of 5.46 minutes is the uninodîil transversal seiche 

 of Yainanaka lake. 



