ALMANAC READERS.

The following data may be found useful in studying an Almanac.

The columns for SUNRISE AND SUNSET are nearly the same year after year for any given place; for by the alteration of styles and the day allowed at Leap Year the civil and astronomical year are almost exactly the same; but the difference in latitude of different places makes a London almanac useless for sunrise and sunset, say at Edinburgh. The sun rises at each place to a greater height in June than in December, but he is always at a less height in Edinburgh than in London both in winter and summer, Edinburgh being farther than London from the equator, where the sun is more immediately overhead.

The RISING AND SETTING OF THE MOON vary greatly day by day. The moon is constantly moving eastward, and she is not moving in the same path with the sun; the latitude and longitude of the observer's position, the place of the moon in her orbit, the rapidity of her motion, and other particulars, are to be taken into account in computing her rising and setting.

The Golden Number is a term arising from the discovery that the sun performs his annual course 19 times to the moon's 235. The golden number is the number which any given year holds in the Lunar Cycle. After the lapse of 19 years the new moons occur on the same days of the same months as before. This discovery being esteemed by the Romans to be highly important, they set up the rule for ascertaining the number of the year in the Lunar Cycle in a tablet with letters of gold, hence the term Golden Number. To find the year of the Lunar Cycle add one to the present year, then divide by 19 and the remainder will show the year of the Cycle.

The Epact is the number of days which must be added to a lunar year to complete a solar year. Twelve lunar months being nearly 11 days less than the solar year, the new moons in one year falling 11 days earlier than in the year preceding it, it becomes necessary on the fourth year, when the difference would amount to 33 days, to take off 30 days as an intercalary month, during which the moon has made a revolution, and the three remaining would be the epact or 'addition,' which thus continues to vary until the 19 years have expired, and the new moons recur as before.

The Solar Cycle is complete in 28 years, after which the days of the month return to the same days of the week as before.

The Dominical or Sunday Letter, as one of the first seven letters of the alphabet, used to denote the days of the week, one of which must of course fall on the Sunday throughout the year. Owing to Leap Year their order every fourth year is disturbed, so that the Solar Cycle must pass round before the letters can fall to the same days of the week.

The Number of Direction. The Council of Nice having decided, A.D. 325, that Easter Day is always the first Sunday after the full moon which happens upon or next after the 21st of March, it follows that Easter Day cannot take place earlier than the 22nd of March, or later than the 25th of April. The number of Direction is that day of the 35, on which Easter Sunday falls.

Roman Indiction was a period of fifteen years, appointed by the Emperor Constantine, A.D. 312, for the payment of certain taxes. It was observed by the Greek and Roman Churches.

The Julian Period consists of 7980 years, produced by the multiplication into each other of the Solar and Lunar Cycles and the Roman Indiction, 28×19×15=7980. This period is reckoned from 709 before the Creation of the World, when the three Cycles are supposed to have commenced together; the lapse of the entire period will be A.D. 3267.

Equation of Time is the difference between the time as indicated by a sun-dial, and that by a good clock. It is necessary because the sun, the chief agent in measuring time, does not upon all days of the year appear to move equally fast, inasmuch as an hour by a sun-dial, correctly indicating the sun's motion, is sometimes longer, sometimes shorter, than an hour by the clock, the hours of which are supposed to be perfectly equal, although the sun's are not. The Equation of Time shows how many minutes are to be added to, or subtracted from, sun-dial time in order to show clock time. The same table of equation will serve all over the world. [See following pages for Equation Table.]

True or Solar Time is that marked by the sun, and it is taken at the moment when he has attained his greatest height above the horizon,—such a moment being of course dependent upon the latitude of the place of observation. The solar time by which our nautical standard is fixed, is that of the meridian of Greenwich.

Sidereal Time is that measured by the fixed stars, which are at such an immense distance from the earth that the diurnal motion of the earth brings these stars to the meridian at sufficiently regular intervals. It is necessary, however, to remember when making observations for sidereal time that these must be made from fixed or twinkling stars, not from planets.

Of the various Eras from which time has been dated, the following are the chief:—

A.M. Anno Mundi. The Year of the World, dating from the Creation, according to Jewish Calendar 5635

The Deluge, Era of, variously reckoned 2348 to 3155 B.C. The first Olympiad 776 B.C. A.U.C. or Anno Urbis Conditæ, the year of the building of Rome 753 B.C. The Hegira, or Flight of Mahomet from Mecca to Medina 622 A.D. The Birth of Christ in the year of the World 4004 The Jewish year 5635 commenced Sept. 12, 1874 A.D.

A TABLE OF THE EQUATION OF TIME,

For regulating Clocks and Watches for 1875.

DayJanuaryFebruaryMarchAprilMayJune

13m.fa.45s.13m.fa.50s.13m.fa.50s.4m.fa. 1s.3m. sl. 0s.2m. sl.30s.

34 4114 412 113 253 142 12

55 3614 1611 452 493 261 51

76 29 14 2411 162 143 351 30

97 2014 2910 471 413 431 7

118 914 3010 161 83 480 44

138 5514 299 430 363 510 19

159 3914 249 90 53 510 fa. 6

1710 2014 168 350 sl. 243 500 31

1910 5814 67 590 523 460 57

2111 3313 537 231 183 401 23

2312 513 376 461 423 321 48

2512 3413 196 92 53 222 14

2713 012 585 322 253 102 39

2913 22 - - - 4 552 442 553 4

3113 41 - - - 4 19 - - - 2 39 - - -

EQUATION OF TIME, 1875—

continued

.

DayJulyAugustSeptemberOctoberNovemberDecember

13m.fa.28s.6m.fa. 5s.0m.sl. 3s.10m.sl.16s.16m.sl.18s.10m. sl.52s.

33 515 570 4110 5416 1910 5

54 135 471 2011 3016 179 17

74 33 5 342 012 516 128 26

94 525 192 4112 3816 47 33

115 95 23 2213 1015 526 38

135 244 424 413 4015 375 42

155 384 204 4714 815 184 45

175 493 555 2914 3314 563 47

195 593 296 1214 5614 312 47

216 63 16 5415 1714 21 48

236 112 317 3615 3413 300 48

256 131 598 1715 4912 550 fa. 12

276 141 268 5816 112 171 12

296 120 529 3716 1011 362 11

316 80 16- - -16 16- - -3 10

Note.—Fa. means clock to be fast, that is, your Clock, to be right, must be so much faster than the Sun-Dial—Sl. that your Clock must be so much slower than the Sun-Dial. To set a Clock or Watch on any Day by means of this Table:—Take out the number of Minutes and Seconds which stand against that day, and make your Clock or Watch so much faster or slower (according as the table is marked fa. or sl.) than the time on a good Sun-Dial. Thus, on January 1st, the Clock must be set 3m. 45s. faster or before the Dial; on the 1st of October, it must be set 10m. 16s. slower. Correct the Watch when the Dial marks just an hour, as 9, 10, 11, 1, 2, 3, or 4 o'clock. Noon is not best, nor near Sunrise or Sunset.

JOHN CHILDS AND SON, PRINTERS.