of integral sums of six specified frequencies. The six, 

 determined by Doodson, are shown in Table 1. 



Table 1. 



f~ = 1 day (period of Earth's rotation relative to Sun) 



_ 1 



f , ' = 1 month (period of Koon' s orbital motion) 

 f~1 = 1 year (period of Sun's orbital motion) 

 f~1 ^ 8085 years (period of lunar perigee) 



G 



f"'' ■v 18.61 years (period of regression of lunar nodes) 

 e 



f"'' ^ 20,900 years (period of solar perigee) 



fk - S, f^ + S^ f^ - - - S^ ff, S=0, ± 1, t 2, - - - 



Fortunately for the purposes of the tidal spacecraft 

 experimental computations, the five constituents already 

 described (Mg, N^, Sj, Kn and 0-, ) ordinarily include more 

 than 95^ of the total energy in a tidal prediction and there- 

 fore the experiment could meaningfully be constrained to 

 solving for the harmonic constants of these five. 



The spectrum of sea level should be mentioned briefly. 

 Figure 5 (presented in a lecture by Walter Munk) is a log- 

 log presentation of the complete spectrum. The high energy 

 in the very low frequencies is primarily due to thermal 

 causes for periods greater than a month and to barometric 

 variations for periods between a day and a month. The tidal 



26-11 



