greater whereas if neap and apogean tides coincide, there 

 are particularly small ranges at these times. 



In his opening remarks, Dr. Stewart mentioned unusually- 

 large tides occurring at the time of this meeting. Not only 

 are M^, Sp and N2 in phase, but another constituent Kp is 

 also. Kp modulates the S^ constituent in a six month period, 

 being in phase with Sp at the time of the equinoxes. 



Thus far, the moon has been constrained to the plane 

 of the earth's equator whereas it actually has extreme de- 

 clinations, both north and south, of as much as 2S^ . Figure 

 2 shows the tidal configuration of the earth with the moon 

 at extreme north declination. As the earth rotates, a point 

 experiences two high tides of different heights (high water 

 inequality). This can be considered as a diurnal tide 

 superimposed on the semidiurnal tide. To simulate a diurnal 

 tide that is large at extreme declination and small (or zero) 

 when the moon is on the equator, two diurnal constituents, 

 K-| , and 0-, , are introduced. These two have circular orbits 

 of about 23.93 and 2$. 82 hours respectively, so that they 

 are in phase at extreme declination and opposed a week later 

 when the moon is on the equator. Furthermore, the sum of 

 their hourly speeds (in degrees per hour) exactly equals 

 the Mp speed so that the phase relationship of the principal 

 semidaily and daily tide remains fixed although the amplitude 

 relationship varies over a 14-day period. 



26-6 



