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:—

JOHN CHILDS AND SON, PRINTERS.