Division of time.-The year. autumnal and vernal equinoxes. These intervals are at present nearly as follows: From the Spring equinox to the summer solstice 92 21 45 93 13 35 186 11 20 178 18 29 7 16 51 The Julian year, so named by Julius Cæsar, who established it, consists of 365 days, 6 hours; but the 6 hours were not reckoned till the expiration of every fourth year, when, amounting just to one day, they were added to the end of February, and the year in which they were thus reckoned was called bissextile or leap year. The Julian year exceeding the true solar year more than 11 minutes, the excess amounts to a whole day in 131 years; in consequence of which, the vernal equinox, which in the first Julian year fell on the 25th of March, had in the year of our Lord 325, at the time of the council of Nice, gone back to the 21st, and in 1582 to the 11th of March. To correct this growing error, the calendar was again amended, under the auspices of Pope Gregory XIII, by taking 10 entire days out of it. Accordingly, in the year 1582, the day following the 4th of October, instead of being called the 5th was called the 15th; by means of which the real equinox was restored to the 21st of March. Provisions were at the same time made, to prevent the recurrence of so important an error again. The intercalary or bissextile day, which had been regularly added to February every fourth year, was ordered to be suppressed at the end of every century not divisible by 4. The last year of the 17th, 18th, and 19th centuries are not leap-years, because 4 will not divide these numbers without a remainder; but the last year of the 20th century, or year 2000, will be a leap-year. This pope's correction of the calen der is so near the truth, that it will not err a day in 3000 years; it is called the Gregorian or the New Style, and obtains in almost all Christian nations. It was not used in England before 1752, when it was adopted pursuant to act of parliament, and the third of September was reckoned the fourteenth, the error of the Julian calendar having at that time increased to 11 days. The lunar year is the space of 12 lunar months, and is either astronomical or civil. Division of time.-The year-Cycles and infiction. The lunar astronomical year consists of twelve lunar synodical months; and is, therefore, 354 days, 8 hours, 48, 38', being 10 days, 21 hours, 11 shorter than the solar year. The lunar cral year is either common or embolimic. The common lunar year consists of 12 lunar civil months, and contains 354 days. The embolimic lunar year, consists of 13 lunar civil months, and contains 384 days. The ancient Roman year, as first settled by the Romans, contained only 10 months, and in all 304 days. The Egyptian year, called also the year of Nabonassar, contains only 365 days, divided into twelve months of 30 days each, with five intercalary days added at the end. Thus the Egyptian year loses a whole day of the Julian year every four years, and after the space of 1460 years, it begins with the Julian year, which length of time is called the Lothic period. The ancient Greek year consisted of 12 months, which at first were divided into 30 days each; but afterwards each month contained 29 and 30 days alternately; and this year was computed from the first appearance of the new moon, with the addition of an embolimic month of 30 days, every 34, 5th, 8th, 11th, 14th, 16th and 19th year, in order to keep the new and full moons to the same seasons of the year. Not only the length of the year, but the time of its commencement, has been differently reckoned among different nations. The Chaldeans and Egyptians commenced their year at the autumnal equinox. The Jews reckoned their civil year from the same period, but began their ecclesiastical year in the spring. Some of the Grecian states commenced their year at the vernal equinox, others at the autumnal equinox, and some at the summer solstice. The Roman year at one time began in March, but afterwards was made to commence in January. The new year's day of the church of Rome is fixed on the Sunday nearest the full moon of the vernal equinox. In England, the year began in March, till 1752, when the style was altered, and the year was at the same time settled to commence on the 1st of January. The part of the year between the 1st of January and the 25th of March, was expressed thus: 1735-6, or 1734, forms of writing which have now become obscure. Of the Lunar and Solar Cycles and Indiction. A cycle is a perpetual circulation of a certain fixed and determinate space of time. The cycle of the sun consists of 28 years; at the end of which time, the days of the months return again to the same days of the week, and the sun is in the same sign and degree Division of time.-Cycles.-Epochs and eras. of the ecliptic, which he was in at its commencement; at least, this is the case within a degree for 100 years. The leap-years, also, at the expiration of the solar cycle, begin the same course over again with respect to the days of the week on which the days of the months fall. The cycle of the moon, the year of which is called the golden number, is a period of 19 years, at the end of which time, the sun and moon return to the same situation in the heavens, or very nearly so: the conjunctions, oppositions, &c. of these two luminaries being within about an hour and a half of being the same as they were on the same days of the months at the commencement of the period. The cycle of indiction, or Roman indiction, has no reference to any natural period. It consisted of 15 years, and was in use only among the Romans, for some civil purposes which cannot now be completely ascertained. The year of our Saviour's birth, according to the usual computation, was the ninth year of the solar cycle; the first year of the lunar cycle; and the 312th year after his birth was the first year of the Roman indiction. With this data, the year of any subsequent cycle or indiction may be found. Of Epochs and Eras. Any remarkable event or period from which time is reckoned, is called an epoch; the years computed from an epoch, or from such event or period, are called an era, whatever be their number. The earliest and most memorable epoch connected with mundane affairs, is that of the creation of the world; but the era referring to it is only continued to the birth of Christ. According to Archbishop Usher, whose chronology is adopted in the current translation of the Bible, it began in the year 4004 before Christ. Playfair places it in 4007. The next epoch was the Deluge, and like the former it was used by the Jews. The epoch adopted by all Christians is that of the birth of Christ; the common estimation of which, making the present year of the Christian era 1813, is supposed to be 4 years too late. The reason of this uncertainty is, that the Christian era was not used till the sixth century after the birth of Christ, when it was too late to fix it with indisputable accuracy. as all the nations who use it, begin at the same time, and the year 1813, for example, is with all of them the year 1813, the error introduces no confusion. But Division of time.-Olympiads.—Julian period.-Abstract of astronomy. The mode of reckoning by olympiads, or periods of four years, was used by the Greeks. The first olympiad began 775 years before the birth of Christ. The Romans reckoned from the building of Rome; the date of that event is, however, not well ascertained, from the want of authentic records in those early times; but the computation adopted by the Romans themselves, places it in the year 753 before Christ. The Hegira, or Mahometan era, takes date from the flight of Mahomet to Medina, 622 years after the commencement of the Christian era. To obtain common standard in the comparison of dates and eras, Joseph Scaliger, adopted a very ingenious method: By multiplying into each other, the cycle of the sun, which is 28 years; the cycle of the moon, which is 19 years; and cycle of indiction, which is 15 years, he obtained the number 7980, which is called a Julian period. This period is supposed to commence 706 years antecedently to the creation, and till the expiration of it, or till the world is 7274 years old, the first years of each of these cycles will not come together.The year of the Julian period corresponding with any given year before or since the commencement of the Christian era may easily be found. If the year required be since the Christian era, add to it 4713, the number of years elapsed before the Christian era, and the sum will be the year required. If the year required precede the Christian era, subtract the year before Christ from 4713, and the difference will be the answer. ABSTRACT OF ASTRONOMY. 1. The solar system, comprises the sun and all the bodies that revolve round him, viz. the comets, the planets with their respective satellites, and the asteroids. 2. The number of the comets is unknown; that of the plancts, so far as yet discovered, is seven, the satellites eighteen ; and the asteroids four. 3. The figure of the earth is not that of a perfect globe, but an oblate spheroid, flattened a little at the poles, by its revolution on its axis. 4. The planets Jupiter and Saturn are also observed to be flattened at the poles like the earth, but in a greater degree, evidently because their diurnal revolution is swifter. Abstract of astronomy. 5. The orbits of all the planets, asteroids and comets, are ellipses, having the sun in one of their foci; but the orbits of the two former classes of bodies are very nearly circles, while the orbits of the comets are all very eccentric. 6. The orbits of the satellites are also ellipses, in one of the foci of which is situated the primary planet round which they move. 7. The periods, distances, and magnitudes of the planets, have all been determined with very considerable exactness; the same circumstances respecting the asteroids, are also evidently determinable, though the results yet laid down, have not, from the recent date of their discovery, been so amply confirmed, as to be fully relied on; but the comets recede to such immense distances, and there is so much uncertainty in identifying them, that their elements are hypothetical. 8. The planets, comets and asteroids, are preserved in their orbits, by the joint effects of the power of attraction, which acts in a right line from them to the sun, and a projectile or centrifugal force, which would carry them off in a tangent to the curve of revolution. 9. The powers which preserve the satellites in their orbits, are the same as those that act upon the planets and comets, but the centripetal force is exercised by the primary. 10. The body of the sun is supposed to be opake, and to be surrounded with a double set of clouds, the upper stratum of which, forms the luminous globe we behold. 11. The planets revolve round an imaginary line or axis within themselves, and the time in which they perform this rotation, constitutes their day and night. 12. The time in which a planet revolves round the sun, forms its year. 13. The diversity of seasons is occasioned by the inclination of the axis of a planet to the plane of its orbit. 14. The annual and diurnal revolutions of the planets are all performed from west to east. 15. The satellites also revolve from west to east, with the exception of the satellites of the Herschel, which appear to move in a contrary direction. 16. The fixed stars are distinguished from the bodies of the solar system, by the twinkling light they afford, by their having no parallax, and by their having, even through the best telescopes, no sensible magnitude. 17. The naked eye cannot behold above five hundred stars in the whole hemisphere; but the number discovered with the assistance of a telescope exceeds all calculation. 27 VOL. I. 4 L |