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under the actual circumstances the line of nodes iscarried round in the manner represented in fig. 45,Plate XI. As the earth moves from e v where theline of nodes n 7 e, n\ is directed towards the sun,the nodes regrede, slowly at first, and with alterna-tions of advance, but more rapidly, and with shorterperiods of advance, until the earth is in positionnot quite one-fourth of a revolution from e v At thistime the line of nodes is square to the line from thesun. As the earth passes on to e 5 the line of nodes stillregredes on the whole, but with longer and longeralternations of advance, until when the earth is at e sthe line of nodes has the position n 5 e 5 n\, or is againdirected towards the sun. The regression recom-mences, and is continued with increasing effect to theposition e 7 , and thence with diminishing effect to theposition e 3 * The actual nature of the nodal regres-sion, as the earth passes through the nine stages,e„ e i> e s> &- c -, is indicated in the figure 45a, exceptthat no account is here taken of the intermittence ofthe regression. Instead of a complete year beingoccupied by the moon’s return in this way to a posi-tion where the rising node is again in conjunctionwith the sun as at first only 346'60 7 days are so occu-
* The inclination decreases as the earth moves from 6i to«»thence increases as the earth moves to e 6t decreases as the earthmoves to e,, and finally increases as the earth moves to
It is to be particularly noticed that e, is not a fixed point on theearth’s orbit, as the vernal equinox or the like. It is simply thepoint where, at the particular time illustrated, the nodal linen#is directed towards the sun.