Page:Encyclopædia Britannica, first edition - Volume I, A-B.pdf/556

 ASTRONOMY. Frorp the Ihifting of the equinp&ial points, and with as in the following example, for 5763 years; which, at them all the figns of the ecliptic, it follows, that thofe the autumnal equinox, A. D. 1756, is thought to be the liars which, in the Infancy of aflronomy, were in Aries, age of the world. So that with regard to the fixed are now got into Taurus ; thofe of Taurus into Gemini, ftars, the equino&ial points in the heavens have receded 6 c. Hence likewife it is, that the flats which rofe or 2s 200 2 2,0" fince the creation; which is as much as let at any particular feafon of the year, in the times of the fun moves in 8id 5h om 52s. And fince that time, Heftod, Eudoxius, Virgil, Pliny, 6c. by no means an- or in 5763 years, the equinoxes with us have fallen back fwer at this time to their defcriptions. The preceding 44d 5h 2im 9s; hence, reckoning from the time of the table fhews the quantity of this fhifting both in the hea- Julian equinox,D. 1756, viz. Sept, nth, it apvens and on the earth, for any nnmber, of years to pears, that the autumnal equinox at the creation was on 25,920, which compleats the grand celeftial period; the 25th of Odlober. within which any number and its quantity is eafily found. Preceffion of the Equinoftial Points in Anticipation of the Heavens. the Equinoxes on the Earth. Julian years. D. H. M. S. D. H. M. S. 9 26 40 70 10 58 20 38 8 50 o 9 20 44 to 5 8 55 o o9 4350 20o o 20 rl7 30 o 11 3 o 60 O 2 30 O I o 52 o o 33 9 3 20 2 30 81 5 o 52 44 $ 21 9 5763 already mentioned the caufe of the precelllon The anticipation of the equinoxes, and confequently of Having the equinodlial points in the heavens, which occafions ' of the feafons, is by no means owing to the preceffion of a How deviation of the earth’s axis from its parallelifm, the equinodfiaband folftitial points in the heavens, (which and thereby a change of the declination of the liars from can only affeft the apparent motions, places, and declinations of the fixed liars), but to the difference between the equator, together with a flow apparent motion of forward with refpedl to the figns of the eclipthe civil and folar year, which is 11 minutes 3 feconds; ticthe; liars lhall now defcribe the phenomena by a diagram. the civil year containing 365 1 days 6 hours, and the fo- In wePlate XLIII. fig. 2. let NZSFL be the earth, lar year 365 days 5 hours qS minutes 57 feconds. A its axis produced to the Harry heavens, and terThe above 11 minutes 3 feconds, by which the civil SON in A, the prefent north pole of the heavens, or Julian year exceeds the folar, amounts to 11 days in minating 1433 years; and fo much our feafons have fallen back which is vertical to AThe north pole of the earth. Let the equator, T'o^Z-the tropic of Cancer, and with refpedt to the days of the months, fince the time EOj^be the tropic of Capricorn; VOZ the ecliptic, and of the Nicene Council in A. D. 325, and therefore in VTrs order to bring back all the falls and fellivals to the days its axis, both which are immoveable among the liars. then fettled, it was requifite to fupprefs 11 nominal days. But as the equinoftial points recede in the ecliptic, the And that the fame feafons might be kept to the fame earth’s axis SONs in motion- upon the earth’s centre 0, times of the year for the future, to leave out the bilfex- in fuch a manner as to defcribe the double cone and and SOs, round the axis of the ecliptic BO, in the time tile day in February at the end of every century of years that the equinoftial points move quite round the ecliptic, not divifible by 4 ; reckoning them only common years, as the 17th, 18th, and 19th centuries, viz. the years which is 25,920 years; and in that length of time, the 1700, 1800, 1900, 6c. becaufe a day intercalated e- north pole of the earth’s axis produced, defcribes the circle ABCDA in the Harry heavens, round the pole of very fourth year was too much, and retaining the bilfex- the ecliptic, which keeps immoveable in the centre of tile-day at the end of thofe centuries of years which are divifible by 4, as the 16th, 20th, and 24th centuries, that circle. The earth’s axis being 23-r degrees inclined to the axis of the ecliptic, the circle ADCDA, defcriviz. the years 1600, 2000, 2400, 6c. Otherwife, in bed by the north pole of the earth’s ajtis produced to A, length of time, the feafons would be quite reverfed with regard to the months of the year; though it would have is 47 degrees in diameter, or double the inclination of required near 23,783 years to have brought about fuch the earth’s axis. In confequence of this, the point A, which at prefent is the north pole' of the heavens, and a total change. If the earth had made exa&ly 365^ near to a Har of the fecond magnitude in the tail of the diurnal rotations on its axis, whillt it revolved from any equino&ial or folilitial point to the fame again, the civil conflellation called the Little Bear, mull be deferted by and folar years would always have kept pace together, the earth’s axis, which moving backwards a degree every B in and the llyle would never have needed any alteration. 72 years, will be direfted towards the liar or point 6480