The Sun and Moon, by attracting this redundancy of matter, bring the Equator sooner under them in every return towards it than if there was no such accumulation. Therefore, if the Sun sets out, as from any Star, or other fixed point in the Heavens, the moment he is departing from the Equinoctial or either Tropic, he will come to the same again before he compleats his annual course, so as to arrive at the same fixed Star or Point from whence he set out.

When the Sun arrives at the same [[56]]Equinoctial or Solstitial Point, he finishes what we call the Tropical Year, which, by long observation, is found to contain 365 days 5 hours 48 minutes 57 seconds: and when he arrives at the same fixed Star again, as seen from the Earth, he compleats the Sidereal Year; which is found to contain 365 days 6 hours 9 minutes 141⁄2 seconds. The Sidereal Year is therefore 20 minutes 171⁄2 seconds longer than the Solar or Tropical year, and 9 minutes 141⁄2 seconds longer than the Julian or Civil year, which we state at 365 days 6 hours: so that the Civil year is almost a mean betwixt the Sidereal and Tropical.

[PLATE VI].

247. As the Sun describes the whole Ecliptic, or 360 degrees, in a Tropical year, he moves 59ʹ 8ʺ of a degree every day; and consequently 50ʺ of a degree in 20 minutes 171⁄2 seconds of time: therefore, he will arrive at the same Equinox or Solstice when he is 50ʺ of a degree short of the same Star or fixed point in the Heavens from which he set out in the year before. So that, with respect to the fixed Stars, the Sun and Equinoctial points fall back (as it were) 30 degrees in 2160 years; which will make the Stars appear to have gone 30 deg. forward, with respect to the Signs of the Ecliptic in that time: for the same Signs always keep in the same points of the Ecliptic, without regard to the constellations.

A Table shewing the Precession of the Equinoctial Points in the Heavens, both in Motion and Time; and the Anticipation of the Equinoxes on Earth.
Julian years.Precession of the Equinoctial Points in the Heavens. Anticipation of the Equinoxes on the Earth.
Motion.Time.
S.°ʹʺDaysH.M.S.D.H.M.S.
1000500020171⁄200113
20014000403500226
300230010521⁄200339
400320012110004412
5004100141271⁄2005515
600500214501618
700550022221⁄2011721
800640024220012824
900730032371⁄2013927
1000820032255015030
2000164006455003410
3000250010845053130
40003320013314007220
500041400165435091230
6000500020173001130
7000582002340250125330
800164013320014440
90011501626150163430
100012320194910018250
2000246402193820112500
3000410045273027150
400053320515164031400
5000656407155032050
60008200810550414300
700094320920441058550
800011640116332063200
90001229012162230621450
100001353201421140716100
200002746402842320158200
3000111400426350230300
4000125332056846403016400
500029264070105820388500
6000223200841310046100
7000371320981521405317100
8000321640112173320619200
9000450012619450691300
1000041853201402156407617400
2000097464028119532015311200
259201200036560019821360

Fig. IV.

To explain this by a Figure, let the Sun be in conjunction with a fixed Star at S, suppose in the 30th degree of ♉, on the 20th day of May 1756. Then, making 2160 revolutions through the Ecliptic VWX, at the end of so many Sidereal years, he will be found again at S: but at the end of so many Julian years, he will be found at M, short of S: and at the end of so many Tropical years, he will be found short of M, in the 30th deg. of Taurus at T, which has receded back from S to T in that time, by the Precession of the Equinoctial points ♈ Aries and ♎ Libra. The Arc ST will be equal to the amount of the Precession of the Equinox in 2160 years, at the rate of 50ʺ of a degree, or 20 min. 171⁄2 sec. of time, annually: this, in so many years, makes 30 days, 101⁄2 hours; which is the difference between 2160 Sidereal and Tropical years: And the Arc MT will be equal to the space moved through by the Sun in 2160 times 11 min. 3 sec. or 16 days, 13 hours 48 minutes, which is the difference between 2160 Julian and Tropical years.

248. From the shifting of the Equinoctial points, and with them all the Signs of the Ecliptic, it follows that those Stars which in the infancy of astronomy were in Aries are now got into Taurus; those of Taurus into Gemini, &c. Hence likewise it is, that the Stars which rose or set at any particular season of the year, in the time of Hesiod, Eudoxus, Virgil, Pliny, &c. by no means answer at this time to their descriptions. The preceding table shews the quantity of this shifting both in the heavens and on the earth, for any number of years to 25,920; which compleats the grand celestial period: within which any number and its quantity is easily found; as in the following example, for 5763 years; which at the Autumnal Equinox, A. D. 1756, is thought to be the age of the world. So that with regard to the fixed Stars, the Equinoctial points in the heavens, have receded 2s 20° 2ʹ 30ʺ since the creation; which is as much as the Sun moves in 81d 5h 0m 52s. And since that time, or in 5763 years, the Equinoxes with us have fallen back 44d 5h 21m 9s; hence, reckoning from the time of the Julian Equinox, A. D. 1756, viz. Sept. 12th, it appears that the Autumnal Equinox at the creation was on the 26th of October.

Julian years.Precession of the Equinoctial Points in the Heavens. Anticipation of the Equinoxes on the Earth.
Motion.Time.
S.°ʹʺD.H.M.S.D.H.M.S.
500029264070105820388500
700094320920441058550
6000500020173001130
3002300105200339
5763220230815052445219

The anticipation of the Equinoxes and Seasons.
[PLATE VI].