Note N. 53 — SECTION II.

Note 53, p. 9. Inclination of an orbit. Let S, fig. 12, be the centre of the sun, P N A n the orbit of a planet moving from west to east in the 438direction N p. Let E N m e n be the shadow or projection of the orbit on the plane of the ecliptic, then N S n is the intersection of these two planes, for the orbit rises above the plane of the ecliptic towards N p, and sinks below it at N P. The angle p N m, which these two planes make with one another, is the inclination of the orbit P N p A to the plane of the ecliptic.