OF ASPECT, ROTATION, AND LIBKATION. 159

the moon travels were invariable, she would cross theecliptic at the two fixed points which would be hernodes. During any single revolution of the moonthis is not far from the actual case; so that we maysay without gross error that in a sidereal month themoon is twice on the ecliptic, and twice at her greatestdistance north and south of the ecliptic, that is, about5° 8' (on the average) north and south of that circle.Viewing the matter in this way for the moment, letus inquire in what way the moon’s range north andsouth of the equator, and her motions generally, asseen from the earth, are affected, according as hernodes lie in different parts of the ecliptic.

Let SENW (fig. 58, Plate XIII.) represent theplane of the horizon, N being the north point, andlet SPN be the visible celestial sphere. LetE M W JE' be the celestial equator, the arrow on thiscircle showing the direction of the diurnal motion,and let WeEe' be the ecliptic, the arrow showingthe direction of the sun’s annual motion. The studentwill understand of course that the ecliptic is onlyplaced, for convenience of drawing, in such a positionas to cross the equator on the horizon at E and W.Twice in each day it occupies that position, as it is

for want of any better word. Accordingly I retain the use of theword, and would suggest, as the best remedy against its defects,that writers should carefully avoid the use of the word to indicateplace, adopting instead the word situation. I give, then, thisdefinition :—Planes are said to have the same position when linesnormal to them have the same direction.