194 Long Waves in Canals and Standing Waves in Closed Basins 



period of the fundamental oscillation. If the Haff is completely enclosed, 

 we find 9 7 h. The influence of the opening on the side consists in a decrease 

 of the period by about 1 -7 h. 



In the case of the Kurisches Haff, conditions are more complicated. Me- 

 rian's formula, assuming this Haff to be closed near Memel, gives for the 

 period of the fundamental oscillation 7-6 h, Defant's method according to 

 Lettau only 7 h, which decrease is understandable, because the narrowing 

 of the lake at one end causes it. The observed period, however, is 9-2 h. The 

 opening of the Haff near Memel cannot be the cause of this considerable 

 increase. Only the exact records of oscillatory conditions of the Kurisches 

 Haff can eliminate this disagreement. 

 (d) Standing Oscillations in Adjacent Seas 



Because of the large horizontal dimensions of the basins, the period of 

 these free oscillations will be very great, sometimes one day and more. The 

 superposition of smaller partial oscillations and forced oscillations (e.g. tides) 

 will often cover up the free oscillations. These are the main reasons why the 

 free oscillations of the adjacent seas have thus far been so little investigated, 

 even though such work is indispensable for clearing up all oscillatory pheno- 

 mena in these seas, including the tides. 



Neumann (1941, p. 180) investigated the Baltic seiches-like oscillations 

 which have already been described for some sections in the Baltic. The variations 

 of its sea level designated by Meissner (1922, p. 121) as "seiches of the Baltic" 

 cannot be the free oscillations of the entire Baltic, on account of the shortness 

 of their periods, but they are merely oscillations of smaller sections of bays 

 and shores. The free oscillations of the Baltic became very important from 

 a practical point of view when they were associated with the sometimes 

 disastrous floods in the inner Gulf of Finland (Leningrad). Stenij (1936) 

 has shown that the free oscillations of the water-masses of the Baltic are one 

 of the causal factors for these floods. It was attempted by Dubnow (1936) 

 to consider the oscillations of the Baltic by means of a basin model, 

 but there is no good agreement between the results of his experiments and the 

 actual observations. Neumann was the first to investigate the free oscillations 

 by analysing accurately the tide gauge observations distributed over the entire 

 coast, in order to study simultaneously oscillatory processes. The existence of 

 free oscillations all over the Baltic was in this way satisfactorily proven. 

 A statistical examination of the variations of the sea surface in Ystad (southern 

 point of Sweden) and Koivisto (at the head of the Gulf of Finland) for the 

 years 1935 and 1936 gave the most frequent period, which was for both loca- 

 lities 26-75-28-25 h, on the average 27-5 h, which is the uni-nodal seiche in 

 the system Baltic-Gulf of Finland .* 



* A shorter period between 25 and 26 h in Koivisto, which is lacking in Ystad, might be the 

 oscillation of the Gulf of Finland itself. 



