How do the tides run?

A. They must flow from east to west; for they must necessarily follow the moon's motion, which is from east to west.

This course of the tides, however, is sometimes interrupted by, the continents and other large tracts of land. The tide, for instance, in the Indian ocean, being stopped by the eastern coast of Africa, must necessarily flow south, towards the Cape of Good Hope; which having passed, it then runs northward, along the western coast of Africa, and that of Spain, Portugal, and France; part enters the English channel, and there meets the tide from the German ocean, running a contrary way, and is necessarily stopped, which produces a very great swell of the water the rest proceeds north, towards the pole.

As to the tides in rivers, they must always flow in a direction directly the reverse with their natural stream; for the waters of the sea being higher, they must necessarily flow into them, and make their waters flow back, or regurgitate.

CLOUDS, MISTS, AND DEW.

2. You mentioned clouds, how are they composed?

A. Clouds are nothing else but a collection of misty vapours, suspended aloft in the air, and soaring on the wings of the wind in a state so condensed, as to appear like substantial bodies. 2. Pray how high do you suppose the clouds to fly ?

A. From about a quarter of a mile to a mile, It is common for persons, by climbing very high mountains, to get above the clouds, and see them

swim beneath them, and, as it were, brushing the side of the mountains they are on.

2. Whence come the various figures and cofors of the clouds?

A. The wonderful variety in the colors of the clouds, is owing to their particular situation with regard to the sun, and the different reflections of its light; the various figures of the clouds result from their loose and voluble texture, revolving into any form according to the different force of the winds.

2. How are mists formed?

A. Mists are those collections of vapours produced by the heat, and which chiefly rise from fenny moist places, and become more visible as the light of the day decreaseth.

2. From what is the dew produced?

A. From a quantity of particles of water extremely subtle, that float about in a calm and serene air in form of vapours; these, 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.

2. What is rain?

RAIN.

A. Thick clouds condensed by the cold, which, by their own weight, fall towards the earth and are broken into small quantities, called drops of

water.

If the cloud that melts is greatly rarified, and its particles in falling, meet an air moderately warm, these drops will be so small, that they will not compose rain but mists only.

2. Are not those countries near the tropics subject to rain?

A. They are-and the rain is considered as being produced from a phenomenon called a water spout or an absorption of water, from the sea, from lakes or rivers, into the clouds, whence it is discharged in torrents of rain.

OF HAIL AND SNOW.

What is hail ?

A. Hail is formed when the parts of the cloud, beginning to fall in large drops meet in their descent a very cold air, which freezes them, and form ice, which are very near the figure and size the drops of water would have been had they fallen.

2. How is snow formed?

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

2. Why are these 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 in chrystals differently arranged, they reflect to us the light from all parts.

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 meeting of two clouds, one charged with electric matter, and the other without a sufficiency to keep up the equilibrium; they meet....and in the fierceness of their motion, burst with a tremendous noise, which is preceded by a flash of lightning or

fire.

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

Light moves almost instantaneously sound moves no more than 1142 feet in a second. That light moves much faster than sound, any one may satisfy himself, by observing a gun discharg ed at a distance, for he will see the fire long before he hears the sound.

The continuation and repetition of the sound is caused by a kind of echo formed in the clouds, to which many hard bodies on the earth may. contribute, which return those rollings or reverberations we hear after a great clap of thunder. 2. I have heard talk of thunder-bolts and their strange effects, pray what are they?

A. What is mis-called a thunder-bolt, is a solid and most rapid flame, which, with incredible swiftness, flies from the clouds to the earth, and passes through every thing opposed to its It sometimes kills men and animals, burns and overthrows large trees and buildings.

course.

V

CLASS IX....LESSON VII.

EARTHQUAKES.

What is an earthquake?

A. A sudden motion caused by the inflammation of some sulphurous and bituminous substances contained in the bowels of the earth not far from its surface.

Naturalists attribute them to both airand water, and that very truly. To comprehend this more easily, it must be remarked, that the surface of the earth is like a shell, beneath which there are an infinite number of cavities and canals, sufficient to contain a considerable quantity of air, water, &c. which, attempting to rush out vio lently, cause those extraordinary tremblings of the earth....Others, however, are of opinion, that earthquakes are not so much owing to the explosion of any sulphurous matter, or the expansion of any winds or vapours in the bowels of the earth, as to the electric matter rushing along the surface of it, and perhaps communicating with that within.

Dr. Stukely was the first who advanced this opinion, in support of which he urged many specious arguments. In the first place, he says, that in the earthquake which happened at London, on the 20th September, 1750, and which affected an extent of country 30 miles in diameter, had it arisen from a subterraneous explosion, it must have moved an inverted cone, or, which is the same thing, a solid body of earth in the shape of a sugar loaf turned upside down, whose base was 30 miles, and its axis or depth, 15 or 20 miles; an effect which, he affirms, no natural power could produce.