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serene air in form of vapors, which being condensed by the coldness of the night, lose by degrees their agitation, and many uniting together fall in the evening in small invisible particles like an extremely fine and delicate rain, which continues but a short time, and is seen in drops of water like pearls upon leaves and herbs.

LESSON IV.

SNOW.

2. How is snow formed?

A. Snow is produced thus: In winter the regions of the air are intensely cold, and the clouds finding this great cold on every side, quickly pass from that state of condensation that might reduce them to rain, into that which is able to reduce them to ice; so that in winter, as soon as the clouds begin to change into fine drops of water, each of these small particles freeze, and, touching each other, form flakes of snow.

2. Why are those flakes so light, and the snow so white?

A. The small intervals that the flakes leave between them, like so many pores, filled with a subtile air, are the cause of their lightness.

The snow is white, because the small particles of ice that compose those flakes being hard,solid, transparent, and differently arranged, they reflect to us the light from all parts.

OF HAIL.

Hail is formed when the parts of the cloud beginning to fall, meet in their descent a very

cold

cold air, which freezes them, and these small bits of ice are very near the figure and size the drops I of water would have been, had they fallen.

THUNDER AND LIGHTNING.

2. What is thunder?

A. A noise heard in the air, most frequently in the summer. Thunder is the most wonderful of all meteors.

2. What is the cause of this meteor?

A. Thunder is caused by the nitrous or sulphurous particles of the clouds, taking fire through the fierceness of their motion, occasioned by strong winds, and bursting with a tremendous noise, which is preceded by a flash of fire or lightning.

The reason we do not hear the dreadful noise of the thunder so soon as we see the lightning, is, because sound is longer arriving to our ears, than light to our sight.

The continuation and repetition of the sound is caused by a kind of echo formed in the clouds, to which many hard bodies upon the earth may contribute, which return those rollings we hear after a great clap of thunder.

21 have heard talk of thunderbolts and their strange effects; pray what are they?

A. What is called a thunderbolt is nothing but a solid and most rapid flame, which, with incredible swiftness, flies from the clouds to the earth, and through every thing standing in its way, being interrupted by nothing. It sometinies kills men and animals, burns and overthrows large trees and buildings, and sets fire to every thing in its way.

OF

Of the Iris, or Rainbow, and Halos. Q. What is the Iris, or rainbow?

A. A beautiful arch in the heavens, ornamented with various colors, that is only seen when the spectator turns his back to the sun, and when it rains on the opposite side. Its colors are, beginning from the under part, violet, indigo, blue, green, yellow, orange, red.

Q. What was the opinion of the ancients concerning this meteor?

A. Its beautiful colors struck antiquity with amazement. To the philosophers Pliny and Plutarch, it appeared as an object which we might admire, but could never explain. The priests always preferred the wood on which the rainbow had appeared to rest for their sacrifices, vainly supposing that this wood had a perfume peculiarly agreeable to their deities.

Q. Please to explain a little how the rainbow is produced, and how it acquires its beautiful and wonderful form?

A. Some philosophers of the obscure ages began to form more just conceptions concerning this meteor; but as they were ignorant of the true causes of colors, they left the task unfinished for Newton to complete. It is made,

according to his theory, by the rays of the sun being refracted by the drops of falling rain or anist, and thence reflected to the spectator's eye.

Q. You have said nothing of the rainbows that sometimes appear by night in the moonshine; what think you of them?

A. The lunar rainbow is formed exactly in the same manner, by the bright beams of the moon striking upon the bosom of a shower. Q. How

Q. How do you account for that lucid ring we see diffused round the moon called an halo?

A. As this always appears in a rimy or frosty season, we may suppose it occasioned by the refraction of light in the frozen particles of the air.

THE AURORA BOREALIS.

What is the cause of the Aurora Borealis, or that shining light that is often seen by night in the heavens, and which the vulgar call northern lights or streamers?

A. They may be the result of certain nitrous and sulphurous vapors thinly spread through the atmosphere above the clouds,where they ferment, and taking fire, the explosion of one portion kindles the next, and the flafhes succeed one another, till the vapor is set on fire, the streams whereof seem to converge towards the zenith of the spectator, or that point of the heavens which is immediately over his head.

EARTHQUAKES.

Q. What is an earthquake?

A. A sudden motion caused by the inflammation of some sulphurous and bitumenous exhalations contained in the caverns of the earth, not far from its surface. In the southern countries

earthquakes are very frequent.

Naturalists attribute them both to air and water, and that very truly. To comprehend this more easily, it must be remarked that the surface of the earth is, as it were a shell, beneath which there is an infinite number of cavities and canals, sufficient to contain a considerable quantity of air, water, &c. which, attempting to rush

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out violently, causes those extraordinary tremblings of the earth.

Q. Are there not many subterraneous places in the earth, from which issue torrents of smoke and of flames, rivers of melted metals, and clouds of ashes and stones ?

A. Yes, they are called volcanoes; the most famous are those of mount Etna in Sicily, Vesuvi

us,

in Naples, and Hekla in Iceland. The bowels of these burning mountains,contain sulphur, bitumen, and other inflammable matter, the effects of which are more dreadful than those of thunder or of gunpowder, and they have in all ages astonished mankind, and desolated the earth.

LESSON V.

OF TIDES.

PRAY what is meant by the tides, or alternate flux and reflux of the fea?

A. As rivers flow and swell, so also does the sea; like them it has its currents, that agitate its waters, and preserve them from putrefaction. This great motion of the ocean is called its tides. The waters of the ocean have been observed regularly from all antiquity to swell twice in about four and twenty hours, and as often to subside again.

In its influx the sea generally rises for six hours, when it remains, as it were suspended, and in equilibrio, for about twelve minutes; at that time it is called high water.

In its reflux the sea falls for six hours, when it remains, as it were, in a like manner suspend

ed,

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