yy s. Nakamiira and K. Honda: 



The reason why it was not observed at Katada and Seta, the two 

 other stations on that part of the lake, must be sought for in the 

 fact that tlie observations at tliese places were of too short duration. 

 The next long period is 72. G minutes, which was observed a few 

 times at Ötsu, Katada and Seta but was not distinct. This might 

 induce us to conclude that this motion is also a characteristic of the 

 southern basin. Our experiments with a model of the lake, 

 however, showed that it is a longitudinal seiche extending over 

 the whole lake. A model of the lake was made in cement on a 

 scale of 90000 : 1 for length and of 1085 : 1 for depth. The gravest 

 longitudinal vibration had a period of ti = 1.58 sec, which on 

 reduction gave a period of 71.9 minutes for the actual lake. The 

 photographic picture of this mode of vibration is reproduced in 

 Plate VII, Fig 1., which shows that it has two nodes, one across 

 the north basin from a point near Katsuno to a point lying between 

 Hikone and Chomeiji, and the other in the south basin so that 

 water meets and recedes from both sides at a place a little north 

 of the narrow neck, or near our station at AVani. On closing up 

 this narrow neck, and setting the water in oscillation, we found 

 that the uninodal motion of the north basin had a nearly equal 

 period, but the south basin could not be set into vibration. Hence 

 it is proper to say that the motion of the seventy-minute period is 

 the uninodal seiche of the north basin, rather than to say that it 

 is a binodal motion of the lake. The forced vibration in the south 

 basin excited by it has however owing to its small depth a greater 

 amplitude than in the north basin, and this is the reason why this 

 particular niotion Avas observed only in the southern stations of 

 Otsu, Katada, and Seta. Again from the bathymétrie data fur- 

 nished by Maeda's map we find that the total volume of the lake 

 is 2.762x10'" c. cm., which divided by the total surface area 



