76 S. Nakamiira and K. Honda. 



§ 6. Hamana Lake. 



Hamana lake is situated at 138°43' E. and 34°44' N. It is 

 connected with the Pacific Ocean by a narrow channel formed by 

 the destructive earthquake which took place on the 20th of Septem- 

 ber, 1498. Its form is very complex being formed by smaller 

 lakes joined by narrow canals and has a number of small arms 

 (Plate XIV). The main lake is more than 5 kilometers long and 

 from 2 to 3 kilometers wide. By our soundings it was found to be 

 very shallow, being only two or three meters deep in most places. 

 Even at the deepest point, which lies at the entrance of a small 

 canal connecting the main lake with a smaller lake on the north, 

 it is only a little more than 16 meters deep, so that it must be 

 said; that it is most unsuitable for observing the phenomena of 

 seiche. The interest, however, lies rather in the opposite direc- 

 tion, that is, in studying whether in such shallow lakes, an oscil- 

 latory motion of the wdiole mass of "water can by any means be 

 excited, and also in searching for the effect of the tides in it. 



Owing to its excessive shallowness and to the influence of the 

 tides, which produced sometimes a double amplitude of about 10 

 centimeters, the proper seiches were very difficult to produce, 

 and even when produced, they were soon damped away, so that it 

 was rather hard to detect and pick them out from the records 

 (Plate XV). We set up three limnimeters of the " N " type at 

 Washizu, Horié and Osaki, and took curves extending over four 

 days. We succeeded only in isolating the following periods from 

 the records. 



