Seiches in Some Lakes of Japan. 



19 



PI. II. 1,2. The motion there had an extraordinarily long period 

 of 231.2 minutes, though the motion most frequently observed 

 in this lake has a period of about 30 minutes. At this place we 

 Iieard the sound of distant thunder at about 13 h. 40 m., and at 

 14 h. 20. m. the shower arrived and then the level of the lake 

 began to rise considerably and afterwards sunk very much. The 

 storm ceased practically at 17 h., and the lake became apparently 

 very calm, but the oscillation continued till tlie evening of the 

 next day, executing nine oscillations with decreasing amplitudes, 

 and then died away. The readings of high and low water levels 

 from an arbitrary datum line are as follows; 



TABLE II. 



High water 



Low water 



Gale, amplitude 



148 mm. 





78 mm. 





mm. 



70 



122 





52 





44 



28 



97 





27 





56 



14 



79 





9 





GO 



10 



78 





8 





60 



10 



From these numbers, the logarithmic decrement was found to be 

 -^=0.1452, so that the damping factor is k= 1.408, and the position 

 of the level at equilibrium is 70 mm.. The calculated successive 

 amplitudes are given in the last column of the above table. The 



