Principal Features of Tidal Phenomena 



249 



is sufficient to determine the principal components, especially if these ob- 

 servations can be tied in to those made at main stations with an extensive 

 record of observations. Figure 105 gives for two successive months (March 

 and April) the tides for Immingham (North Sea, east coast of England) in 



Fig. 105. Tide curves for Immingham (east coast of England) for March and April 1936 

 (Horn). The O of the left-hand scale corresponds to the chart datum. The phases of the moon 

 are below the time scale. N and S indicate the time of the greatest northern and southern 

 declination; Q the time when the moon crosses the equator; A and P, the time of the Apogee 



and Perigee. 



the form of tidal curves (see Horn, 1943, p. 411). The zero of the height 

 scale at the left side corresponds to the chart datum. The inequalities in time 

 are too small on this horizontal scale to be noticeable. But the variation 

 in height between spring and neap tides is quite clear. The phases of the 

 moon and its other positions are indicated below the time; the difference 

 of the tidal curves from one-half month to the next one shows the influence 

 of the inequalities. The small diurnal inequality is characteristic of the tides 

 at the North Sea. 



The essence of tidal phenomena was in part already known to the an- 

 cient Greeks and Romans, before the first attempt at a mechanical expla- 

 nation was successful. In the Mediterranean the tides are not so well 

 developed. However, from the literature on other sea regions it is apparent 

 that the ancient scientists had a certain good knowledge of the tides and 

 were also capable of applying it. The first to write on this subject was Herodo- 

 tus, who mentioned the tides in the Gulf of Suez. Strabo reports on the 

 views held by Posidonius (deceased in B.C. 51) and Aristotle on the tides near 

 Cadiz and by Seleucus on those in the Red Sea. The spring tides and their 



