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THE PLANETARY SYSTEM.

125

LESSON 57.

The Planetary System.

FAIR star of eve, thy lucid ray

Directs my thoughts to realms on high;
Great is the theme, though weak the lay,
For my heart whispers 'God is nigh.'
The Sun, vicegerent of his power,
Shall rend the veil of parting night,
Salute the spheres, at early hour,
And pour a flood of life and light.
Seven circling planets I behold,
Their different orbits all describe;
Copernicus these wonders told,
And bade the laws of truth revive.

Mercury and Venus first appear,
Nearest the dazzling source of day ;
Three months compose his hasty year,
In seven she treads the heav'nly way.
Next, Earth completes her yearly course;
The Moon as satellite attends;
Attraction is the hidden force,
On which creation's laws depend.

Then Mars is seen of fiery hue;
Jupiter's orb we next descry;
His atmospheric belts we view,
And four bright moons attract the eye.

Mars soon his revolution makes,

In twice twelve months the sun surrounds;
Jupiter, greater limit takes,

And twelve long years declare his bounds.

With ring of light, see Saturn slow,
Pursue his path in endless space;
By seven pale moons his course we know,
And thirty years that round shal trace.

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THE PLANETARY SYSTEM

The Georgium Sidus next appears,
By his amazing distance known ;
The lapse of more than eighty years,
In his account makes one alone.

Six moons are his, by Herschel shown,
Herschel of modern times the boast;
Discovery here is all his own,
Another planetary host!

And lo! by astronomic scan,

Three stranger planets track the skies,
Part of that high majestic plan,

Whence those successive worlds arise.

Next Mars, Piazzi's orb is seen,

Four years six months complete his round;
Science shall renovated beam,

And gild Palermo's favoured ground.

Daughters of telescopic ray,

Pallas and Juno, smaller spheres,

Are seen near Jove's imperial way,

Tracing the heavens in destined years.

Comets and fixed stars I see,

With native lustre ever shine;

How great! how good! how dreadful! He,
In whom life, light, and truth combine.

Oh! may

I better know his will,

And more implicitly obey;

Be God my friend, my father still,
From finite-to eternal day.

MANGNALL.

NOTE. The foregoing rhymes were made, probably, before Vesta was discovered, and some of the facts, relating to the other new planets, not so well ascertained as at present. Ceres is sometimes called Piazzi, after the discoverer.

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CHEMISTRY is an instructive, interesting, and valuable science. Within the last sixty years its empire has been wonderfully extended. There is scarcely an art of human life which it is not fitted to subserve; scarcely a department of human inquiry or labour, either for health, pleasure, ornament, or profit, which it may not be made in its present improved state, eminently to promote. To the husbandman this science furnishes principles and agents of inestimable value.

It teaches him the food of plants, the choice and use of manures, and the best means of promoting the vigour, growth, productiveness, and preservation of the various vegetable tribes. To the manufacturer chemistry has lately become equally fruitful of instruction and assistance. In the arts of brewing, tanning, dyeing, and bleaching, its doctrines are important guides. In making soap, glass, pottery, and all metallic wares, its principles are daily applied, and are capable of a still more useful application, as they become better understood. Indeed, every mechanic art, in the different processes of which heat, moisture, solution, mixture, or fermentation is necessary, must ever keep pace in improvement with this branch of philosophy. To the physician this science is of still greater value, and is daily growing in importance. He learns from it to compound his medicines, to disarm poisons of their force, to adjust remedies to diseases, and to adopt general means of preserving health. To the student of natural history chemistry furnishes instruction at every step of his course. To the public economist it presents a treasure of useful information. By means of this science alone can he expect to attack with success the destroying pestilence, and to guard against other evils to which the state of the elements gives rise. And to the successful prosecution of numberless plans of the philanthropist, some acquaintance with the subject in question seems indispensably necessary. Finally, to the domestic economist this science abounds with pleasing and wholesome lessons. It enables him to make a proper choice of meats and drinks; it directs him to those measures with respect to food, clothing, and

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GENERAL PRINCIPLES

respiration, which have the best tendency to promote health, enjoyment, and cheapness of living; and it sets him on his guard against many unseen evils, to which those who are ig norant of its laws are continually exposed. In a word, from a speculative science, chemistry, since the middle of the eighteenth century, has become eminently and extensively a practical one. From an obscure, humble, and uninteresting place among the objects of study, it has risen to a high and dignified station; and instead of merely gratifying curiosity, or furnishing amusement, it promises a degree of utility, of which no one can calculate the consequences or see the end.

QUESTIONS.-1. What does chemistry do for the husbandman ? 2. For the manufacturer? 3. For the mechanic arts? 4. For the physician? 5. For the student of natural history? 6. For the public economist ? 7. For the philanthropist? 8. For the domestic eco

nomist?

LESSON 59.

General Principles of Chemistry.

THE object of chemistry is to ascertain the ingredients of which bodies are composed,-to examine the compounda formed by those ingredients,-and to investigate the nature of the power which produces these combinations. The science therefore naturally divides itself into three parts: a description of the component parts of bodies, or of elementary or simple substances as they are called,-a description of the compound bodies formed by the union of simple substances, and an account of the nature of the power which produces these combinations. This power is known in chemistry by the name of affinity, or chemical attraction.

By simple substances is not meant what the ancient phi losophers called elements of bodies, as fire, air, earth, and water, nor particles of matter incapable of farther diminu tion or division. They signify merely bodies that have never been decomposed, or formed by art. The simple substances of which a body is composed are called the constituent parts of that body; and, in decomposing it, we separate its con

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stituent parts. If, on the contrary, we divide a body by cutting it to pieces, or even by grinding it to the finest powder, each of these small particles will consist of a portion of the several constituent parts of the whole body: these are called the integrant parts. Compound bodies are formed by the combination of two or more simple substances with each other.

Attraction is that unknown force which causes bodies to approach each other. Its most obvious instances are, the gravitation of bodies to the earth; that of the planets towards each other, and the attractions of electricity and magnetism. But that attraction, which comes under the more immediate cognizance of chemists, subsists between the particles of bodies; and when it operates between particles of the same species, it is called the attraction of cohesion, or the attraction of aggregation; but when between the particles of different substances, it is called the attraction of composition, chemical attraction, or chemical affinity. The attraction of cohesion, then, is the power which unites the integrant particles of a body: the attraction of composition that which combines the constituent particles. When particles are united by the attraction of cohesion, the result of such a union is a body of the same kind as the particles of which it is formed; but the attraction of composition, by combining particles of a dissimilar nature, produces compound bodies quite different from any of their constituents. If, for instance, you pour upon a piece of copper, placed in a glass vessel, some of the liquid called nitric acid (aqua fortis) for which it has a strong attraction, every particle of the copper will combine with a particle of acid, and together they will form a new body, totally different from either the copper or the nitric acid. If you wish to decompose the compound which you have thus formed, present to it a piece of iron, for which the acid has a stronger affinity than for copper; and the acid will quit the copper to combine with the iron, and the copper will be what the chemists call precipitated, that is to say, it will be thrown down in its separate state, and reappear in its simple form. In order to produce this effect, dip the blade of a knife into the fluid, and when you take it out you will observe that, instead of being wetted with a bluish liquid like that contained in the glass, it will be covered with a thin coat of copper.

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