Tides of the Oceans 503 



of an ocean from the boundary conditions of the problem. Properly speak- 

 ing, it is not a theory of the tides of the ocean because this would also have 

 to include the proof as to why each tide wave occurs with its phase and 

 amplitude in the given form. 



Hansen (1949) has used his method, given in Chap. XI, p. 368 to compute 

 the semi-diurnal tides of the Atlantic Ocean. By means of this method iso- 

 lines of water level are obtained for the North Atlantic. It is shown that 

 there is a fairly good agreement in magnitude between the observations on 

 North Atlantic islands and the corresponding values derived theoretically 

 from coastal observations. Figure 201a contains these theoretical tides of 

 the Atlantic, giving isolines of high-water difference referred to the upper 

 transit of the moon through the Greenwich meridian as well as co-tidal lines 

 of the semi-diurnal tide M.,. 



