Part 14

+------------------------------------------------------------------+ | _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_. | +--------+--------------------------------------++-----------------+ | | Precession of the Equinoctial || Anticipation of | | | Points in the Heavens. || the Equinoxes | | Julian +----------------+---------------------++ on the Earth. | | years. | Motion. | Time. || | | +----------------+---------------------++-----------------+ | | S. ° ʹ ʺ | Days H. M. S. || D. H. M. S. | +--------+----------------+--------------------++------------------+ | 1 | 0 0 0 50 | 0 0 20 17-1/2 || 0 0 11 3 | | 2 | 0 0 1 40 | 0 0 40 35 || 0 0 22 6 | | 3 | 0 0 2 30 | 0 1 0 52-1/2 || 0 0 33 9 | | 4 | 0 0 3 20 | 0 1 21 10 || 0 0 44 12 | | 5 | 0 0 4 10 | 0 1 41 27-1/2 || 0 0 55 15 | +--------+----------------+---------------------++-----------------+ | 6 | 0 0 5 0 | 0 2 1 45 || 0 1 6 18 | | 7 | 0 0 5 50 | 0 2 22 2-1/2 || 0 1 17 21 | | 8 | 0 0 6 40 | 0 2 42 20 || 0 1 28 24 | | 9 | 0 0 7 30 | 0 3 2 37-1/2 || 0 1 39 27 | | 10 | 0 0 8 20 | 0 3 22 55 || 0 1 50 30 | +--------+----------------+---------------------++-----------------+ | 20 | 0 0 16 40 | 0 6 45 50 || 0 3 41 0 | | 30 | 0 0 25 0 | 0 10 8 45 || 0 5 31 30 | | 40 | 0 0 33 20 | 0 13 31 40 || 0 7 22 0 | | 50 | 0 0 41 40 | 0 16 54 35 || 0 9 12 30 | | 60 | 0 0 50 0 | 0 20 17 30 || 0 11 3 0 | +--------+----------------+---------------------++-----------------+ | 70 | 0 0 58 20 | 0 23 40 25 || 0 12 53 30 | | 80 | 0 1 6 40 | 1 3 3 20 || 0 14 44 0 | | 90 | 0 1 15 0 | 1 6 26 15 || 0 16 34 30 | | 100 | 0 1 23 20 | 1 9 49 10 || 0 18 25 0 | | 200 | 0 2 46 40 | 2 19 38 20 || 1 12 50 0 | +--------+----------------+---------------------++-----------------+ | 300 | 0 4 10 0 | 4 5 27 30 || 2 7 15 0 | | 400 | 0 5 33 20 | 5 15 16 40 || 3 1 40 0 | | 500 | 0 6 56 40 | 7 1 5 50 || 3 20 5 0 | | 600 | 0 8 20 0 | 8 10 55 0 || 4 14 30 0 | | 700 | 0 9 43 20 | 9 20 44 10 || 5 8 55 0 | +--------+----------------+---------------------++-----------------+ | 800 | 0 11 6 40 | 11 6 33 20 || 6 3 20 0 | | 900 | 0 12 29 0 | 12 16 22 30 || 6 21 45 0 | | 1000 | 0 13 53 20 | 14 2 11 40 || 7 16 10 0 | | 2000 | 0 27 46 40 | 28 4 23 20 || 15 8 20 0 | | 3000 | 1 11 40 0 | 42 6 35 0 || 23 0 30 0 | +--------+----------------+---------------------++-----------------+ | 4000 | 1 25 33 20 | 56 8 46 40 || 30 16 40 0 | | 5000 | 2 9 26 40 | 70 10 58 20 || 38 8 50 0 | | 6000 | 2 23 20 0 | 84 13 10 0 || 46 1 0 0 | | 7000 | 3 7 13 20 | 98 15 21 40 || 53 17 10 0 | | 8000 | 3 21 6 40 | 112 17 33 20 || 61 9 20 0 | +--------+----------------+---------------------++-----------------+ | 9000 | 4 5 0 0 | 126 19 45 0 || 69 1 30 0 | | 10000 | 4 18 53 20 | 140 21 56 40 || 76 17 40 0 | | 20000 | 9 7 46 40 | 281 19 53 20 || 153 11 20 0 | | 25920 | 12 0 0 0 | 365 6 0 0 || 198 21 36 0 | +--------+----------------+---------------------++-----------------+

[Sidenote: 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. 17-1/2 sec. of time, annually: this, in so many years, makes 30 days, 10-1/2 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 2^s 20° 2ʹ 30ʺ since the creation; which is as much as the Sun moves in 81^d 5^h 0^m 52^s. And since that time, or in 5763 years, the Equinoxes with us have fallen back 44^d 5^h 21^m 9^s; 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_.

+---------+----------------------------------++----------------+ | | Precession of the Equinoctial || Anticipation | | | Points in the Heavens. || of the | | Julian +-----------------+----------------+| Equinoxes on | | years. | Motion. | Time. || the Earth. | | +-----------------+----------------++----------------+ | | S. ° ʹ ʺ | D. H. M. S. || D. H. M. S. | +---------+-----------------+----------------++----------------+ | 5000 | 2 9 26 40 | 70 10 58 20 || 38 8 50 0 | | 700 | 0 9 43 20 | 9 20 44 10 || 5 8 55 0 | | 60 | 0 0 50 0 | 0 20 17 30 || 0 11 3 0 | | 3 | 0 0 2 30 | 0 1 0 52 || 0 0 33 9 | +---------+-----------------+----------------++----------------+ | 5763 | 2 20 2 30 | 81 5 0 52 || 44 5 21 9 | +---------+-----------------+----------------++----------------+

[Sidenote: The anticipation of the Equinoxes and Seasons.

PLATE VI.]

249. The anticipation of the Equinoxes, and consequently of the seasons, is by no means owing to the Precession of the Equinoctial and Solsticial points in the Heavens, (which can only affect the apparent motions, places and declinations of the fixed Stars) but to the difference between the Civil and Solar year, which is 11 minutes 3 seconds; the Civil year containing 365 days 6 hours, and the Solar year 365 days 5 hours 48 minutes 57 seconds. The following table shews the length, and consequently the difference of any number of Sidereal, Civil, and Solar years from 1 to 10,000.

[Sidenote: The reason for altering the Style.]

250. The above 11 minutes 3 seconds, by which the Civil or Julian year exceeds the Solar, amounts to 11 days in 1433 years: and so much our seasons have fallen back with respect to the days of the months, since the time of the _Nicene_ Council in _A.D._ 325, and therefore in order to bring back all the Fasts and Festivals to the days then settled, it was requisite to suppress 11 nominal days. And that the same seasons might be kept to the same times of the year for the future, to leave out the Bissextile day in _February_ at the end of every century of years not divisible by 4; reckoning them only common years, as the 17th, 18th and 19th centuries, _viz._ the years 1700, 1800, 1900, _&c._ because a day intercalated every fourth year was too much, and retaining the Bissextile-day at the end of those Centuries of years which are divisible by 4, as the 16th, 20th and 24th Centuries; _viz._ the years 1600, 2000, 2400, _&c._ Otherwise, in length of time the seasons would have been quite reversed with regard to the months of the years; though it would have required near 23,783 years to have brought about such a total change. If the Earth had made exactly 365-1/4 diurnal rotations on its axis, whilst it revolved from any Equinoctial or Solstitial point to the same again, the Civil and Solar years would always have kept pace together; and the style would never have needed any alteration.

[Sidenote: The Precession of the Equinoctial Points.]

251. Having already mentioned the cause of the Precession of the Equinoctial points in the heavens, § 246, which occasions a flow deviation of the earth’s axis from its parallelism, and thereby a change of the declination of the Stars from the Equator, together with a slow apparent motion of the Stars forward with respect to the Signs of the Ecliptic; we shall now describe the Phenomena by a Diagram.

[Sidenote: Fig. V.]

Let _NZSVL_ be the Earth, _SONA_ its Axis produced to the starry Heavens, and terminating in _A_, the present north Pole of the Heavens, which is vertical to _N_ the north Pole of the Earth. Let _EOQ_ be the Equator, _T_♋_Z_ the Tropic of Cancer, and _VT_♑ the Tropic of Capricorn: _VOZ_ the Ecliptic, and _BO_ its Axis, both which are immoveable among the Stars. But, as [57]the Equinoctial points recede in the Ecliptic, the Earth’s Axis _SON_ is in motion upon the Earth’s center _O_, in such a manner as to describe the double Cone _NOn_ and _SOs_, round the Axis of the Ecliptic _BO_, in the time that the Equinoctial points move quite round the Ecliptic, which is 25,920 years; and in that length of time, the north Pole of the Earth’s Axis produced, describes the Circle _ABCDA_ in the starry Heavens, round the Pole of the Ecliptic, which keeps immoveable in the center of that Circle. The Earth’s Axis being 23-1/2 degrees inclined to the Axis of the Ecliptic, the Circle _ABCDA_, described by the north Pole of the Earth’s Axis produced to _A_, is 47 degrees in diameter, or double the inclination of the Earth’s Axis. In consequence of this, the point _A_, which at present is the North Pole of the Heavens, and near to a Star of the second magnitude in the tail of the constellation called _the Little Bear_, must be deserted by the Earth’s Axis; which moving backwards a degree every 72 years, will be directed towards the Star or Point _B_ in 6480 years hence: and in double of that time, or 12,960 years, it will be directed towards the Star or Point _C_; which will then be the North Pole of the Heavens, although it is at present 8-1/2 degrees south of the Zenith of _London L_. The present position of the Equator _EOQ_ will then be changed into _eOq_, the Tropic of Cancer _T_♋_Z_ into _Vt_♋, and the Tropic of Capricorn _VT_♑ into _t_♑_Z_; as is evident by the Figure. And the Sun, in the same part of the Heavens where he is now over the earthly Tropic of Capricorn, and makes the shortest days and longest nights in the Northern Hemisphere, will then be over the earthly Tropic of Cancer, and make the days longest, and nights shortest. So that it will require 12,960 years yet more, or 25,920 from the present time, to bring the North Pole _N_ quite round, so as to be directed toward that point of the Heavens which is vertical to it at present. And then, and not till then, the same Stars which at present describe the Equator, Tropics, polar Circles, and Poles, by the Earth’s diurnal motion, will describe them over again.

_A_ TABLE _shewing the Time contained in any number of Sidereal, Julian, and Solar Years, from 1 to 10000_.