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THE CONSTELLATIONS.

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rays which enter the eye cannot have been less than six years and four months and a half coming from that star to the observer. Hence it follows that when we see an object at the calculated distance, at which one of these very remote nebulæ may still be perceived, the rays of light which convey its image to the eye, must have been more than nineteen hundred and ten thousand, that is, almost two millions of years on their way; and that, consequently, so many years ago, this object must already have had an existence in the sidereal heavens, in order to send out those rays by which we now perceive it.

But when we have reached the utmost distance to which the power of our instruments can penetrate, who will say, that we are approaching any limits of the creation? who will say, that if the disembodied spirit should travel forward through eternity, numberless systems would not be continually spreading before it? All that part of the universe which we are able to discern, is peopled by inhabitants, who have the common want of heat and light; who will say, that there are not other parts of the material universe inhabited by beings of different natures, to whom these wants are unknown? It is only some portion, we know not how small, of the material universe which is obvious to our senses; who will attempt to define the limits of the invisible world? who will attempt to set bounds to the works of infinite power and infinite goodness?

QUESTIONS.-1. What are fixed stars?-why so called? 2. How does it appear that they do not borrow their light? 3. What is said of the magnitude of the stars? 4. Number? 5. Describe the milkyway (or galaxy.) 6. What calculations did Dr. Herschel make? [NOTE. Many stars, single to the naked eye, appear double, triple, and even quadruple, through a telescope. Dr. Herschel found that in more than fifty double stars, a change of situation really takes place : it is concluded, therefore, that they describe orbits round a centre of gravity.]

LESSON 55.

The Constellations.

THE first people who paid much attention to the fixed stars were the shepherds in the beautiful plains of Egypt

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THE CONSTELLATIONS.

and Babylon. Endowed with a lively fancy, they divided the stars into different companies or constellations, each of which they supposed to represent the image of some animal, or other terrestrial object. Of these ancient constellations there were fifty, to which the moderns have added about thirty others. Twelve of these constellations are in the zodiac, bearing the same names with the signs of the zodiac or ecliptic. But these constellations and signs do not coincide, for the equinoctial points are not stationary, but move backward, and the sign Aries always begins at one of them, and all the other signs each succeed Aries in order; it follows therefore that all the signs of the ecliptic or zodiac move backward with the equinoxes. The distance which they move annually is about fifty seconds of a degree; so that with respect to the fixed stars the equinoctial points fall backwards thirty degrees, in about two thousand two hundred years, whence the stars will appear to have gone forward thirty degrees, with respect to the signs of the ecliptic, which are always reckoned from the equinoctial points. This shows the importance of distinguishing between the signs of the zodiac and the constellations of the zodiac; for stars, which are in one sign at one time, will be in the succeeding one at another. Thus, the stars which were formerly in Aries, are now in Taurus, and so on. When these

names were given to the signs and constellations, it is supposed that each sign coincided with the constellation of the same name; but on account of this moving of the equinoctial points, or, as it is termed, the precession of the equinoxes, there is now about one sign or thirty degrees difference. The period will be completed in about twenty-six thousand years.

Among the northern constellations, none are more remarkable than that which is nearest to the north pole, and termed the little bear. The last star of its tail is but two degrees from the pole; hence it is called the polar star. It is easily distinguished from the neighbouring stars, because it scarcely appears to change its position, and is always in the same part of the heavens. By its fixed situation it becomes a guide to travellers, and particularly to mariners who are sailing on the open seas. Before the discovery of the compass sailors had no surer guide than the polar star; and even now, when the sky is serene, they repose in many cases

HYMN TO THE NORTH STAR.

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with greater certainty upon the direction of this star, than upon the magnetic needle.

Hymn to the North Star.

THE sad and solemn night
Has yet her multitude of cheerful fires;
The glorious host of light

Walk the dark hemisphere till she retires :
All through her silent watches gliding slow,
Her constellations come, and round the heavens, and go.

Day, too, hath many a star

To grace his gorgeous reign, as bright as they:
Through the blue fields afar,

Unseen, they follow in his flaming way.
Many a bright lingerer, as the eve grows dim,
Tells what a radiant troop arose and set with him.

And thou dost see them rise,

Star of the Pole! and thou dost see them set.

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Alone in thy cold skies,

Thou keep'st thy old unmoving station yet,

Nor join'st the dances of that glittering train,
Nor dip'st thy virgin orb in the blue western main.

There, at morn's rosy birth,

Thou lookest meekly through the kindling air,
And eve, that round the earth

Chases the day, beholds thee watching there;
There noontide finds thee, and the hour that calls
The shapes of polar flame to scale heaven's azure walls.

On thy unaltering blaze

The half-wrecked mariner, his compass lost,

Fixes his steady gaze,

And steers, undoubting, to the friendly coast;

And they who stray in perilous wastes, by night,
Are glad when thou dost shine to guide their footsteps

right.

And, therefore, bards of old,

Sages, and hermits of the solemn wood

Did in thy beams behold

A beauteous type of that unchanging good,

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FORMS AND DIVISIONS OF TIME.

That bright eternal beacon, by whose ray

The voyager of time should shape his heedful way.
BRYANT.

QUESTIONS.-1. What is said of the first division of the stars into constellations? 2. Why do not the constellations and signs of the zodiac coincide? 3. What is the present difference between them? 4. At what rate does the change take place? 5. Describe tne situation of the polar star.

LESSON 56.

Forms and Divisions of Time.

As the form of the year is various among different nations, so is its beginning. The Jews, like most other nations of the East, had a civil year, which commenced with the new moon in September; and an ecclesiastical year, which commenced from the new moon in March. The Persians begin their year in the month answering to our June; the Chinese, and most of the inhabitants of India, begin it with the first moon in March; and the Greeks with the new moon that follows the longest day. In England and America, the civil or legal year formerly commenced on the twenty-fifth of March, and the historical year on the first of January. But since the alteration of the style, which took place in 1752, the civil year in both countries has likewise begun on the first of January.

The principal division of the year is into parts called months, which are either astronomical or civil. An astronomical or natural month is that which is measured exactly by the motion of the Earth or Moon, and is accordingly either lunar or solar. A lunar month is the time the moon takes to revolve round the earth, which she performs in twenty-seven days, seven hours, and forty-three minutes. A solar month is that space of time in which the earth runs through one of the signs of the zodiac; as the earth constantly travels through the twelve signs in three hundred and sixty-five days five hours and forty-nine minutes, each solar month is found by dividing this number by twelve, to contain thirty days, ten hours, and twenty-nine minutes.

EQUATION OF TIME.

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Civil months are those which are framed to serve the uses of life, and approach nearly to the quantity of astronomical months either lunar or solar; being made, with the exception of February, to consist of thirty and thirty-one days. To the days of a week, the Pagans gave the names of the sun, moon, and planets; and for the first two days and last day of our weeks, those names are still retained.

A natural or solar day is the time which the sun takes in passing from the meridian of any place till it comes round to the same meridian again; or it is the time from noon to noon. A sidereal day is the time in which the earth revolves once about its axis. The rotation of the earth is the most equable and uniform motion in nature, and is completed in twenty-three hours, fifty-six minutes, and four seconds, for any meridian on the earth will revolve from a fixed star, to that star again in this time. Sidereal days, therefore, are all of the same length; but solar or natural days are not. The mean length of a solar day is twenty-four hours, but it is sometimes a little more, and sometimes less. The reason of the difference between the solar and sidereal day is, that as the earth advances almost a degree eastward in its orbit, in the same time that it turns eastward round its axis, it must make more than a complete rotation before it can come into the same position with the sun that it had the day before; in the same way, as when both the hands of a watch or clock set off together, as at twelve o'clock, for instance, the minute hand must travel more than a whole circle before it will overtake the hour hand, that is, before they will be in the same relative position again. It is on this account that the sidereal days are found to be, on an average, shorter than the solar ones by three minutes and fifty-six seconds.

As a clock is intended to measure exactly twenty-four hours, it is evident that, when a solar day consists of more than twenty-four hours, it will not be noon by the sun till it is past noon by the clock; in which case the sun is said to be slow of the clock. But when a solar day consists of less than twenty-four hours, it will be noon by the sun before it is noon by the clock; and the sun is then said to be fast of the clock. Time measured by a clock is called equal or mean time, and that measured by the apparent motion of the sun in the heavens, or by a sun-dial, is called apparent time. The adjustment of the difference of time, as shown by a

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