196 Long Waves in Canals and Standing Waves in Closed Basins 



exceeds 1 m; towards the entrance of the Gulf of Finland the amplitudes 

 decrease rapidly, and at Landsort and Libau the oscillations have nearly 

 vanished. The south-west part of the Baltic, on the contrary, oscillates in 

 the opposite phase and the amplitudes increase up to Gjedser. From here 

 on, the amplitudes in the south-western part of the Baltic no longer increase; 

 they rather decrease. In the Belts, in Korsoer and Frederica, it is impossible 

 to find a correlation with the oscillatory process of the Baltic except at two 

 extremes. Here as in Copenhagen, the regular tidal oscillations are prepon- 

 derant. Figures 84 and 85 give, for the first oscillation of this case, the two 



Fig. 84. Co-range lines of the oscillation of 11-12 December, 1932 in the Baltic. The dotted 

 lines indicate the amount in cm of depression, the full drawn lines the amount of elevation 



for the first half period. 



extreme positions of the water surface in the entire- area of the Baltic. We 

 can see how well the amplitudes fall along the line of the oscillation, and 

 there is no doubt that we have here the uni-nodal free oscillation of the system 

 Baltic — Gulf of Finland. The observed period is 27-3 h. 



The two-nodal wave appears quite often; however, it has always a smaller 

 amplitude and, in the few cases in which it occurs without the fundamental 

 oscillation, it does not persist after one or two oscillations. It is less persistent 

 than the uni-nodal seiche; the Baltic seems to be less suited for its development. 



There are also free oscillations in the system Baltic — Gulf of Bothnia with 

 a period of about 40 h ; however, in this case the oscillating basin is divided 

 into two unsymmetrical sections by the nodal line, and this is why the oscilla- 

 tions of this basin seldom occur. 



