Seiches in Some Lakes of Japan. ^g 



6.861 X 10'- sq. cm. gives as the mean depth 4.025x 10^ cm.. The 

 length of the lake measured along the deepest line is I/=4.6xl0'' 

 cm., from which it follows that the period of the uninodal longi- 

 tudinal seiche is 77.2 minutes. 



The third u:iotion has a period of 30.5 minutes, and was 

 observed at stations distributed all over the lake, of which it was 

 the predominating oscillation. A glance at the above table shows, 

 however, that at the stations on the northern part of the lake viz., 

 Chikubushima, Hikone, Imazu, and Shiotsu, the period seems to 

 be always smaller than that at the southern stations as at Chömeiji, 

 Katada, and Seta, though there is an exception to this rule at 

 Nagahama. It is possible that we have in reality two different 

 motions with nearly equal periods in the t\vo, parts of the lake. 

 The fact, that the great north basin has two deep places in it, one 

 off Imazu and the other near Wani and Katsuno may furnish a 

 plausible basis for this conjecture ; but we prefer not to enter further 

 into the discussion of this point. Under the supposition that this 

 motion is a transverse seiche of the lake, let us take as the breadth 

 of the lake 2.0x10'' cm., and use the depth before calculated, we 

 then find that the transverse seiche should have a period of about 

 33.6 minutes. It was found with the model lake that it has a 

 stationary motion with a period of t2=0.67 sec, which on reduction 

 corresponds to a period of 30.5 minutes in the actual lake exactly 

 coinciding with the observed value in question. The photographic 

 record of this mode of vibration is reproduced in Plate VII, Fig 2. 

 Careful examination of the change of level in the model showed us 

 that this motion is not so simple as its period might lead us to 

 suppose. The motion is in fact rather transversal in the north 

 part of the north basin, but it has another small node running 

 across its south Jpart, and still another within the south basin. 



