Long Wares in Canals and Standing Waves in Closed Basins 197 



The closing of the Baltic basin towards the Belts is established morpho- 

 logically. The first narrowing of the cross-sections is near the Darser sill 

 (saddle depth only 1 8 m), the second one in the western part of the Fehmarn- 



Fig. 85. Co-range lines for the watermass oscillating back to its original position (see Fig. 84). 



belt near the sandbank Ojet. In both cases the cross-section is only about 

 1/30 to 1/40 of the mean cross-section of the Baltic. If we take the western 

 border line first at the Fehmarnbelt, the second time in the small Belt near 

 the line Aaro-Assens, Neumann obtains for both oscillating systems accord- 

 ing to the methods of Defant and Hidaka, the fundamental period of the 

 Baltic, as listed in Table 26. 



The agreement of the periods computed by fundamentally different methods 

 is very good. Figure 86 shows the theoretical distribution of the vertical 

 (2?7o) and of the horizontal (2£ ) water displacements of the uni-nodal oscilla- 

 tion. The position of the nodal line of this oscillation is not symmetrical, 

 but is somewhat displaced towards the north in the vicinity of the northern 

 point of Gotland. This is in excellent agreement with the observed position 

 (see Figs. 84 and 85). From the entrance in the Gulf of Finland (approxi- 

 mately at cross-section 38) the range increases very rapidly and attains at 

 the eastern end (Leningrad) values which are nearly twice as large as those 

 at the western end (Luebecker Bucht). This is also confirmed by observations. 

 It is remarkable that, for the two-nodal wave, the opposite is true. Due to 

 the large widening and deepening of the Baltic in the middle sections, the 

 greatest horizontal water displacements and, hence, also the greatest current 



