16 OSCILLATIONS OF THE LUNAR TIDES. 



converge towards the equator at each of the solstices. 

 As far as the oscillations of the solar tides are con- 

 cerned, the ebbing and flowing of the annual tide 

 would each year be similar, as regards both the 

 amount of its rise and fall, and the periods of the 

 year at which its alternate ebbing and flowing in 

 each hemisphere occurs. 



176. Let us, however, now consider the oscillations 

 in latitude of the lunar tides. 



When the moon is on the equator, then the culmin- 

 ating points of the lunar tides are also at the equator ; 

 but as the moon diverges from the equator, the lunar 

 and counter-lunar tides diverge equally in opposite 

 directions, in the same manner as do the analogous 

 solar tides. And, as similar positions of the moon in 

 its orbit round the earth do not recur in each succeed- 

 ing year at similar periods of the year, the influence 

 of this oscillation of the lunar tides, in increasing or 

 lessening the height, as well as in retarding or acce- 

 lerating the ebbing or flowing of the annual tide, will 

 vary from year to year. 



177. And since the plane in which the moon 

 moves in its orbit round the earth is inclined to the 

 ecliptic, and the points at which it crosses the ecliptic 

 are constantly changing : therefore the extremes of 

 the moon's declination from the equator must vary 

 in each lunation in accordance with the change in 

 the position of the points at which it crosses the 

 ecliptic. And as these points, or nodes, regress on 



