So, when the Earth is at _E_ and _G_, the Moon is about her Nodes at New and Full; and in her greatest _North_ and _South Declination_, (or Latitude as it is generally called) from the Ecliptic at her Quarters: but when the Earth is at _F_ or _H_, the Moon is in her greatest _North_ and _South Declination_ from the Ecliptic at New and Full, and in the _Nodes_ about her Quarters. [Sidenote: The Moon’s ascending and descending Node. Her North and South Latitude.] 318. The point _X_ where the Moon’s Orbit crosses the Ecliptic is called _the Ascending Node_, because the Moon ascends from it above the Ecliptic: and the opposite point of intersection _V_ is called _the Descending Node_, because the Moon descends from it below the Ecliptic. When the Moon is at _Y_ in the highest point of her Orbit, she is in her greatest _North Latitude_; and when she is at _W_ in the lowest point of her Orbit, she is in her greatest _South Latitude_. [Sidenote: The Nodes have a retrograde motion. Fig. I. Which brings on the Eclipses sooner every year than they would be if the Nodes had not such a motion.] 319. If the line of the Nodes, like the Earth’s Axis, was carried parallel to itself round the Sun, there would be just half a year between the conjunctions of the Sun and Nodes. But the Nodes shift backward, or contrary to the Earth’s annual motion, 19-1/3 degrees every year; and therefore the same Node comes round to the Sun 19 days sooner every year than on the year before. Consequently, from the time that the ascending Node _X_ (when the Earth is at _E_) passes by the Sun as seen from the Earth, it is only 173 days (not half a year) till the descending Node _V_ passes by him. Therefore, in whatever time of the year we have Eclipses of the Luminaries about either Node, we may be sure that in 173 days afterward we shall have Eclipses about the other Node. And when at any time of the year the line of the Nodes is in the situation _VGX_, at the same time next year it will be in the situation _rGs_; the ascending Node having gone backward, that is, contrary to the order of Signs from _X_ to _s_, and the descending Node from _V_ to _r_; each 19-1/3 degrees. At this rate the Nodes shift through all the Signs and degrees of the Ecliptic in 18 years and 225 days; in which time there would always be a regular period of Eclipses, if any compleat number of Lunations were finished without a fraction. But this never happens, for if the Sun and Moon should start from a conjunction with either of the Nodes in any point of the Ecliptic, whilst the same Node is going round to that point again the Earth performs 18 annual revolutions about the Sun and 222 Degrees (or 7 Signs 12 Degrees) over; and the Moon 230 Lunations or Courses from Change to Change and 85 Degrees (or 2 Signs 25 Degrees) over; so that the Sun will be 138 Degrees from the same Node when it comes round, and the Moon 85 Degrees from the Sun.