OF ASPECT.. ROTATION^ AND LIBRATION. 151

July 11th.* Similarly any other case can be dealtwith.

Before passing from this part of our subject, wemay here conveniently consider the phenomena of theharvest moon and of the hunter’s moon.

If the moon moved in the equator, she would riselater night after night by a nearly constant interval;or, in other words, the actual number of hours be-tween successive risings (or settings) would be con-stant. But as she moves on a path considerablyinclined to the equator, this does not happen with herany more than it does with the sun; moreover, as shemoves much more rapidly along the equator than thesun does, the difference is much more perceptible. Ifwe consider two extreme cases, we shall see thereason of this. Let H H', fig. 52, Plate XII., be aportion of the eastern horizon, E the true east point,E Q the equator; and let us suppose that when themoon rises on a certain night she is on the equator atE. She is then carried by the diurnal motion alongE Q to her culmination in the south, and so to hersetting place in the west. Now if her orbital motionwere on the equator, she would be on the next nightat the same hour at a point such as m on the equator(Em being an arc of about 12°12'),and would be carried

* In a work now out of print, called the “ Constellation Seasons,”I introduced a map showing the sun’s diurnal course at differentdates, in such sort that his elevation and bearing at any time couldbo at once ascertained. Such a map serves many useful purposesbesides those for which it is primarily intended.