HARMONIC ANALYSIS. 369 



We thus obtain a practically complete expression which can be used for 

 the systematic prediction of the tides at the port in question. 



f One point of special interest in the Harmonic Analysis is the deter- 

 mination of the long-period tides. It has been already stated that owing to 

 the influence of dissipative forces these must tend to approximate more or less 

 closely to their equilibrium values. Unfortunately, the only long-period tide, 

 whose coefficient can be inferred with any certainty from the observations, 

 is the lunar fortnightly, and it is at least doubtful whether the dissipative 

 forces are sufficient to produce in this case any great effect in the direction 

 indicated. Hence the observed fact that the fortnightly tide has less than 

 its equilibrium value does not entitle us to make any inference as to elastic 

 yielding of the solid body of the earth to the tidal distorting forces exerted by 

 the moon*. 



* Prof. G. H. Darwin, I.e. ante p. 350. 



