in the time of Julius Cæsar, on the 25th of March, was at the time of the Council of Nice, held in the year 325, fixed on the 21st of March, and in 1582 it was found to happen on the 11th. This constant anticipation of the equinox became an object of serious complaint in the 15th century; and in 1474, Pope Sextus IV, being convinced of the necessity of a reformation, sent for Regiomontanus, a celebrated mathematician, and presented him with the archbishopric of Ratisbon, in order to engage him in the undertaking. But a premature death preventing him from the accomplishment of the design, the project was suspended for a whole century. It was now that Pope Gregory XIII had the honour of executing what several preceding Pontiffs and Councils had attempted before in vain. He invited to Rome a considerable number of mathematicians and astronomers, employed ten years in the examination of their several formule; and, finally, gave the preference to the plan proposed by Aloisius and Antonius Lilius, two brothers of Verona. He transmitted copies of this plan in 1577 to all the Catholic states and the learned academies at that time existing. A council of the most learned prelates was convened by the Pope, and, the subject being finally settled, a brief was published in the month of March, A.D. 1582, by which the use of the old calendar was entirely abrogated in all countries over which his Holiness had any sway, and the new one substituted in its stead, called, from his name, the Gregorian Calendar.

The principle adopted was, that the ten days which had been gained by the old account should be taken from the month of October, of the year then current, and the equinox brought back to the 21st of March, as it had been settled by the Council of Nice; and to prevent the future recurrence of a similar variation, it was ordained, that, instead of making every hundredth year a bissextile, as was the case before, every four hundredth year only should be considered as bissextile,

and the rest as common years. The length of the solar year, and the time of the vernal equinox, were, by these means, very accurately settled for as a day was gained, by the former mode of reckoning, in every interval of 130 years, this was nearly equivalent to the gain of three days in every 400 years; and consequently, by making the years 1700, 1800, 1900, to be common years, instead of leap years, the error arising from the odd time would be properly corrected; so that the new mode of reckoning cannot vary a single day from true time in less than 5000 years.

When the Pope had thus reformed the calendar, he ordered all the ecclesiastics under his jurisdiction to conform to this new mode of reckoning, and exhorted Christian princes every where to adopt it in their dominions. Hence it was instantly introduced into almost all Catholic countries. The Catholic states of Germany adopted it, but those that were of the reformed faith rejected it. Hence arose a difference of 10 days between the methods of reckoning afterwards used in Catholic and Protestant countries, In In the year 1700, the reformation of the calendar was introduced into the Protestant states of Germany, and also into Denmark. In Sweden it did not obtain till March 1753. In this country, an act of parliament was passed to cancel eleven days out of the month of September, because, as 170 years had elapsed since the Gregorian alteration had taken place, the old style had consequently gained more than a day upon the course of the Sun than it had at the former period. The old style, then, in Great Britain, and all its dependencies, ceased on the second of September 1752, and the next day, instead of being the third, was called the 14th. By the same act, the beginning of the year was changed from the 25th of March to the 1st of January.

A considerable difficulty still remained, which was. to make the lunar year agree with the solar one, and in settling the true time for the observance of Easter,

and the other moveable feasts. It had been ordered by the Council of Nice, that Easter should be celebrated upon the first Sunday after the first full Moon following the vernal equinox. And in order to the due observance of this rule, it became necessary to know when the full Moons would happen in the course of every year. Now the revolutions of the Sun and Moon are not very obviously commensurate, the solar year containing 12 lunations, and about 11 days; but it had been discovered by Meto, 2000 years ago, that 19 solar years contain exactly 235 lunations; and this determination is so very accurate, that it makes the lunar month only half a minute too long. Hence it happens, that, in every period of 19 years, the Moon's age is the same on the same day of the year. The number of the year in the Metonic circle is called the Golden number, the calendar of Meto having been ordered, at the celebration of the Olympic games, to be engraved in letters of gold on a pillar of marble. At present, if we add 1 to the number of the year, and divide by 19, the remainder will 1814 +1

be the Golden number: thus, for 1814,

1815

19

19 95 and 10 over as a remainder, which remainder 10 is the Golden number.

If we subtract 1 from the Golden number, then multiply by 11 and divide by 30, the remainder will be the epact, which is the Moon's age on the 1st of

January; thus, for 1814, we have 9 (10-1) ×

11

30

99 3 and 9 over, which nine as a remainder is the

30

epact. The application of these numbers will be shown in another part of the volume.

The time of the Sun's rising and setting in London, at intervals during the month of April, is as follows:

Friday
11th
Monday
Thursday 21st

1st, Sun rises 34 m. past 5. Sun sets 26 m. after 6

Equation of Time. [See the month of January.] The following table will show what is to be added to and what is to be subtracted from the apparent time, as shown on the dial, to obtain equal or true time for every fifth day during the month of April.

m. S.

For

Friday - April 1st, to the time on the dial add 4 5

Wednesday

6th

Friday

Thursday-

21st from

Tuesday

26th

The Moon will be full at 29 m. past 8 in the afternoon of the 4th: it enters its last quarter on the 12th, at 23 m. past 9: the change or new Moon is at 55 m. past 7 on the 20th; and it enters its first quarter at 6 m. past midnight on the 26th.

The time of the Moon's rising for the first five days after she is full, is as follows:

Venus will be stationary on the 3d, Mercury on the 15th, and Jupiter on the 27th. The Sun enters the sign Taurus 11 m. past 6 in the evening of the 20th. On the 26th of this month, the Moon will eclipse the star. The immersion will occur at 25 m. past 12 at night, and the emersion at 18 m. after the next morning, the star passing under the Moon's centre. On the 1st, there will be an obscuration of the star A 8 by the planet Mars, the star being 18' north of the centre of the planet; and on the 8th, the same planet will pass over 2 x 8, 29' south.

The greatest elongation of Mercury will be on the 30th, and the inferior conjunction at four o'clock in the afternoon of the 2d. At six in the morning of the 20th, the planet Saturn will be in its quadrature, that is, three signs distant from the Sun.

The eclipses of Jupiter's first satellite, that are visible in these parts, will for April be as follow:3 m. past 10 in the evening.

7th day

14th

22d

23d

30th

These times apply to their emersions.

VIEW OF THE SOLAR SYSTEM.

Venus, the most beautiful star in the heavens, known by the names of the morning and evening star, like Mercury, described in the observations of the last month, keeps near the Sun, though she recedes from him almost double the distance of that planet. She is, however, never seen in the eastern quarter of the heavens when the Sun is in the western, but always seems to attend him in the evening, or, by preceding him, to give notice of his approach in the morning.

This planet offers the same phenomena as Mercury, with this difference, that its phases are much more sensible, its oscillations more extensive, and their period more considerable: her greatest distance from the Sun varies from 45° to nearly 48°, and the mean duration of a complete oscillation is 584 days. The retrograde motion of this planet commences or finishes, when the planet, approaching the Sun in the evening, or receding from it in the morning, is about 27° or 28° distant from it.

Venus, like Mercury, has been sometimes seen, though the phenomenon is extremely rare, moving across the Sun's disk in the form of a round black spot, with an apparent diameter of 59". A few mornings after this has been witnessed, Venus is seen in the morning west of the Sun, if examined with a telescope of very moderate powers, in the form of a

M