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In our present calendars, the days of the week are dis-

tinguished by the first seven letters of the alphabet, A,
B, C, D, E, F, G. The letter A is always put for the
first day of the year; B for the second; C for the third;
and so on in succession to the seventh. Should the 1st
of January fall on a Sunday, the dominical or Sunday
letter for that year will be A, the Monday letter B, and
so of the rest throughout the year. If the year contained
364 days, making an exact number of weeks, it is ob-
vious that A would for ever have been the dominical
letter. The year however, containing one day more, it
follows that the dominical letter of the succeeding year
will be G. For as there are 365 days in the year,
Sunday being the first day of the year, it will also be the
last, and the first Sunday in the following year will fall
on the Seventh day, which will be marked G. Thus the
Sunday letters go back from A to G, from G to F; from
F to E, and so on. If
every year were to consist of 365
days, the process would be regular, and a cycle of seven
years would suffice to restore the same letters to the
same days as before; but the intercalation of a day
every fourth year occasions a variety. The bissextile or
leap year, containing 366 days, will throw the Sunday
letter back two letters, so that in the year 1815 the Sun-

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USITIO

day letter will be A, but in 1816, that being leap year, it will be G till the end of February, and then will be F to the end of the year. Hence twenty-eight years must elapse before a complete revolution can take place in the dominical letter, and a table constructed to shew the dominical letters for any given years of one of these cycles, will answer for the corresponding years in every successive cycle.

These observations I have introduced as preliminary to finding Easter Sunday, which is not only one of the most considerable festivals in the Christian Calendar, but is that which regulates and determines the time of all other moveable feasts. The rule for the celebration of Easter, as fixed by the Council of Nice, is, that it be held on the Sunday which falls next after the first full moon after the vernal equinox. The reason of this decree was that christians might avoid celebrating their Easter at the same time that the Jews celebrate their passover, which was always held the very day of the full moon.

The only difficulty therefore is to find the day when the pascal full moon falls. The rules for finding this, and also the dominical letter * we might readily insert, but as they require some calculation, most of our readers

* To find the dominical letter for any year.-Rute: Divide the hundred of the given year by 4, and subtract twice the remainder from 6; then the sum of this last remainder, the odd years and their fourth, divided by 7 will leave a remainder, which being deducted from 7, shews the index of the dominical letter. Thus for the year 1814.

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Two then is the index of the dominical letter, and as 1 is the index of A, 2 must be the index of B, which is the dominical letter for the year 1814.

will probably prefer a table that renders the finding of Easter Sunday very easy, from the present period to the year 1900.

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We have already shewn that the epact is found by means of the golden number; thus, for the year 1814

The golden number is (18144 95 and 10 over

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over) 10 ) 9

30

Now to find Easter with these data and the foregoing table, we have the epact 9, which corresponds with the 4th of April, whose weekly letter is C, but the Sunday letter of 1814 is B, therefore the first Sunday B after the 4th of April C, will be on the 10th of April, which is Easter Sunday.

Having obtained Easter Day, the other feasts are easily obtained.

The rising and setting of the sun for certain days in the month of May will be as follows:

Sunday 1st Sun rises 37 m. past 4, Sun sets 23 m. past 7.

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The sun enters the sign Gemini at 36 m. past 6 in the afternoon of the 21st: Saturn is stationary on the 11th. Mars eclipses the star marked 132 y passing nearly over the centre: and again on the 27th it eclipses 54' north of the centre.

Equation of Time. [See January.] The following table will shew what is to be subtracted from the apparent time as marked on the dial to obtain equal or true time for each fifth day during the month of May:

Sunday May 1st, from the time on the dial subtract 3

M. S.

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2

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The Moon is at full at 29m. past 10 in the morning of the 4th, it enters its last quarter 41m. past 2 in the afternoon the change or new Moon is at 23m. past 4 on the 19th, and it enters its first quarter at 31m. past 7 in the morning of the 26th. The time of the Moon's rising for the first four days after it is full is as follows:

May 5th, 36m. past 3 in the afternoon.

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Venus will be at her greatest elongation on the 21st day of the month. Jupiter will be in the quadrature at past 11 at night on the 22d, and the Georgian planet will be in opposition to the Sun, that is at the distance of 6 signs, or the two bodies will be in opposite parts of the heavens at 6 in the morning of the 22nd day of the month.

There will be only two eclipses of Jupiter's first satellite visible at Greenwich this month, viz. on the

7th day at 10m. past 12 at night,

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MR. Henry Andrews of Royston, so many years the editor of Moore's, Partridge's, and other almanacks, in advising as to the compilation of a system of prognostic astronomy, so as to be of real and practical utility, recommends the celebrated Lilly, and Henry Coley, as the best guides the English language affords. Without at all derogating from the characters of these two great men, you have in the Mentor Stellarum I observe, hitherto attended the precepts of Ptolomy only, whose rules have been the longest established, enter more deeply into the fundamental parts of science, and appear with respect to generals, for it is only of generals he treats, more consistent to reason, which is the only standard of perfection, than those of any other writer who flourished either before or since his time.

Respecting particulars, Ptolomy says little or nothing in his quadripartite. Content with handing down to us how the heavenly orbs operate on the ambient, whether separately or conjoined, it remained for men like Lilly, whose experience in predictive astronomy in all its adjuncts was more painful and protracted than that of almost any other man, to elucidate general judgments both on the radical horoscope, and on the probable effects of directions, revolutions, transits, profections, &c. But acute as he and his disciple Coley undoubtedly were, and luminous as their opinions have ever been acknowledged, they abound with errors, which appear to have their origin more in the opinions of the age in which they lived than in their own 'understandings; otherwise it is impossible to suppose that Coley, one of the first mathematicians of his day, should have deliberately sat

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