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earth; as when her crescent is brightly displayed, and the other part of her orb is faintly seen.

In consequence of her revolution round the earth, and the different positions in which she reflects the sun's light, the moon appears to experience a continual change of figure.

When the moon is in a line between the sun and the earth, her unenlightened side is turned towards us, and she is not visible; and is, then, called the new moon. When she has advanced through an eighth part of her orbit, a quarter of her enlightened hemisphere is turned towards the earth, and she then appears horned. When the moon has performed a fourth part of her course, she shows one half of her enlightened side, and is then said to be a quarter old.

When she is in her second octant, or eighth portion of her orbit, she displays a larger part of her illuminated hemisphere, and appears humped, or gibbous. When the moon has performed half of her revolution, she then exhibits the whole of her enlightened face, and is full. In her third octant, part of her dark side being turned towards the earth, she is again gibbous. Advancing farther in her decrease, one half of her enlightened side becomes apparent only. When she is in her fourth octant, only one quarter of her illuminated face is visible; and when she has completed her course, the moon again totally disappears. To the inhabitants of the moon the earth must assume the same appearances, but must be seen thirteen times larger.

It was long imagined that the moon had ne

atmosphere; but it is now certain that she has an atmosphere, extending from her body, not farther than 5742 English feet.

Upon an average, the moon rises three quarters of an hour later each day than the preceding one; but about the fifteenth of September, she is so peculiarly situated, that for several successive evenings, she rises later each evening, only by from fifteen to twenty minutes.

To the inhabitants of the regions within the arctic and antarctic circles, the full moon never rises in their summer, when, for a long time, they do not lose sight of the sun; nor sets in their winter, when, for a gloomy season, they are not visited by that glorious luminary.

When viewed through the telescope, the face of the moon appears wonderfully varied; for those dark patches and brilliant spots which are visible to the naked eye, are seen to be immensely high mountains and deep concavities, and prodigiously prominent points. Volcanoes are discernible, and some astronomers assert, that they have seen their flames faintly gleaming. Her mountain scenery (says Dr. Brewster) bears a strong resemblance to the towering sublimity and terrific ruggedness of Alpine regions. Huge masses of rock, rise at once, from the plains, and raise their peaked summits high in air; while projecting crags spring from their rugged flanks, and, threatening the valleys below, seem to bid defiance to the laws of gravitation. Around the base of these frightful eminences, are strewed numerous loose and unconnected fragments, which time seems to have detached

from the parent mass. In some parts, the perpendicular elevation of the mountains is above four miles; and some of the immense hollows are nearly four miles deep, and forty miles in diameter.

QUESTIONS.

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What is the form of the earth, and what hold in the arrangement of the planets? chief proofs of the earth's spherical figure? and at what distance from the sun, does the earth revolve around that glorious luminary? In what earth perform its revolution round the sun? What is that movement of the earth which is called the precession of the equinoxes? What are the effects of the earth's diurnal and annual motions? What is the number of square miles on the earth's surface, and how are they distributed? At what rate does the earth perform her diurnal and annual motions? What secondary planet attends the earth round the sun; at what distance, and in what time, does she revolve round the earth? What is the rate of the moon's motion? By what light does the moon shine? What appearances does the moon assume in different parts of her course? How large must the earth appear to the inhabitants of the moon, and what figures must she present? Has the moon any atmosphere; and if so, what is its extent? What appearances does the moon present through the telescope? Does the moon revolve round her own axis; and if so, in what time? What is the length of the day and night in the moon?

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THOSE risings and fallings of the water, which are observable on all sea-coasts, are called tides.

Were the waters of the ocean always at rest, they would always preserve a certain depth; but experience teaches that they are continually varying from this level, and that some of these variations are regular and periodical.

On the shores of the oceans, and in bays and harbours which communicate freely with the ocean, the waters rise above this mean height twice a-day, and as often sink below it; forming what is called a flood and an ebb, a high and a low water.

The whole interval between high and low water is called a tide; the water is said to flow and to ebb. The rising is named the flood tide, and the falling is called the ebb tide.

It is observed, likewise, that this rise and fall of the waters is variable in quantity; sometimes rising higher and sinking lower; and it is remarked, that these different heights of tide succeed each other in a regular series, diminishing from the greatest to the least, and then increasing from the least to the greatest. The greatest is called a spring tide, and the least is called a neap tide. This series is completed in about fifteen days; and two of these regular processes take place in the exact time of a lunation.

It is remarked, that high water happens at new and full moon.

The time of high water, in any place, appears to be regulated by the moon.

The interval between two succeeding high waters is variable.

The tides in similar circumstances, are greatest when the moon is at her smallest distance from

the earth; and, gradually diminishing, are smallest when she is at her greatest distance. The same holds good with respect to the sun's distance; and the highest tides are observed during the winter months of Europe.

The tides in any part of the ocean increase as the moon, by changing her declination, approaches the zenith of that place. The tides which happen while the moon is above the horizon, are greater than the tides of the same day, when the moon is below the horizon.

Such are the regular phenomena of the tides which were observed by many of the ancient philosophers, but for which they could assign no adequate cause.

The first who gave any rational explanation of these phenomena, was Kepler; who asserted that "The orb of the attracting power, which is in the moon, extends to the earth, and draws the waters under the torrid zone; acting upon places where it is vertical; insensibly on confined seas and bays, but sensibly on the ocean, whose beds are large, and the waters have the liberty of reciprocation, that is, of rising or falling."

And again," The cause of the tides of the sea appears to be the sun and moon, drawing the waters of the sea. The waters of the ocean would all go to the moon, were they not retained by the attraction of the earth." He then explained the cause of the elevation of the waters at one and at the same time, immediately under the moon, and on the opposite side; remarking, that the earth is less attracted by the moon than the nearer waters, but more strongly by the waters

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