Tides of the Oceans 479 



of the behaviour of the tides on the open oceans. Therefore, the maps will 

 always remain quite subjective and will give at their best the probable system 

 of oscillation of the partial tide under consideration. 



Still more difficult than the presentation of the distribution of the phase 

 is the cartographical presentation of the distribution of the amplitudes. It is 

 very difficult to bridge the vast expanses of the oceans by interpolation be- 

 tween the amplitudes given along the coasts, due to the disturbing influence 

 of the varying slope of the continental shelf. 



Dietrich restricted himself to give a distribution of the amplitude along 

 the coasts in the form of a diagram, or to enter its value for a large number 

 of coastal localities. It is true that, in this way, no picture of the distribution 

 of the amplitudes over the entire ocean is given but in using the map of the 

 phase one can roughly visualize the principal features of the distribution of 

 the tidal ranges; this is perhaps preferable to lines, which simulate only an 

 accuracy not existing in reality. 



3. The Charts of the Tides in the Various Oceans 



Charts I and II are, according to Dietrich (1944), the presentation of the 

 co-tidal lines of the semi-diurnal and diurnal tides of the ocean. The M 2 tide has 

 been chosen as representation for the semi-diurnal tide and the tide K x for the diur- 

 nal tide. Another kind of representation of the amplitudes of the semi-diurnal 

 and diurnal tides along the coast of all oceans has been chosen here. It is presen- 

 ted in the charts III and IV. The average tidal range of the ocean surface is 

 indicated by straight lines in these diagrams for the west and east coast of each 

 ocean (ordinates) and with the latitude along the coast as abscissa. Chart III 

 contains the range of the semi-diurnal tide 2(M 2 + So) and chart IV that of the 

 diurnal tide 2(A' 1 + 1 ). An immediate and excellent impression of the distribu- 

 tion of the tidal amplitude along the ocean coast is obtained in this way. This 

 allows a much better insight into the distribution of the amplitudes than any 

 plot of the amplitude values at corresponding coastal places on an ocean chart. 

 The distribution of the characteristic number F = (K x + 0^1(1^0 + S 2 ) along 

 individual coasts has been indicated in the diagram III by different forms 

 of the vertical lines (full, dashed, dashed-dotted or dotted, see text to chart III). 



The principal features of the tides in the total ocean are well explained by 

 these four charts I-IV can be found in the previously mentioned paper of 

 Dietrich. Moreover the co-tidal lines of the two next important tides S 2 and O x 

 have in general the same aspects -as the co-tidal lines of the M 2 and AT 2 tides. 

 This is evidenced by the fact that for vast areas the differences in phase be- 

 tween S 2 —M 2 and K x —O x remain constant. Large discrepancies in this dif- 

 ference in phases for the diurnal tides K 1 —0 1 occur only occasionally (for 

 instance on the European and South African coasts); however, this happens 

 generally when the amplitude is very small and therefore it can probably be 

 attributed to uncertainty in the constants. 



