500 



Tides of the Oceans 



Figures 205 and 206 show that the agreement between theory and observations 

 for amplitude and for the phase is very good. The Atlantic Ocean, therefore, 

 behaves, at least on its centre axis, like a narrow canal. 



100 



50 







-50 



-100 



-150 



100 



50 



i 



-50 



-100 



Azores Bermuda Is Cap Verde Is Fernando Noronfto Ascension St Helena Tnniqod Tnston do Cunno 



8 



12 16 20 24 28 32 36 40 44 48 



Cross- sections 

 Fig. 205. Distribution of the amplitude forhe t 1 h and 4 h waves along the centre axis 

 of the Atlantic Ocean. +, tide observations on Atlantic Islands corresponding to Table 85. 



The phases of the tidal currents also fit well into this theory (Fig. 207); 

 however, the velocities of these currents are in reality greater than given 

 by the theory. This contradiction, however, is explained, if one considers 

 that the rotation of the earth is not taken into account in the theory. Accord- 



Azores Bermuda Is. Cop Verde Is. Fernando Noronho Ascension Si HetenoTrinidod Tnslon da Cunho 



120 



n 80 



40 











8 



hr 4 





 8 



8 



12 



16 20 24 28 32 36 40 44 48 

 Cross-sections 

 Fig. 206. Theoretically computed semi-diurnal tide along the centre axis of the Atlantic. 

 + , observed values on islands; , co-tidal lines according to Sterneck. 



ing to Sverdrup, the rotation of the earth increases the velocity of the tidal 

 currents, above those in a long narrow canal by a factor j 1/1— s 2 , in which 



2cosin0 

 In 



(see equation XL 2). If we multiply by this factor, we have an entirely satis- 

 factory explanation for the observed slow increase of the velocity of the semi- 

 diurnal tidal current to the north. According to this theory, the semi-diurnal 



