there is more or less of a watery vapour passing from the surface of the sea into the air. This vapour is sometimes perceptible, at other times the air may appear quite pure and transparent, and yet be loaded with moisture. This vapour then forms the clouds, which we see of such diversified shapes careering along the sky. When two of these clouds, or two currents of air of unequal temperatures, meet, the consequence is a deposition of moisture in the form of rain; or if the temperature of the atmosphere be at the freezing-point, of snow or of hail. The most plausible explanation of this circumstance appears to be the following::-A current of air, very much heated, is capable of holding suspended a very large portion of moisture,a current of cold air, a moderate portion of moisture. When two currents of hot and cold air are mixed together, then the whole is cooled down to a moderate degree; and hence all the superfluous moisture, incapable of being suspended, falls down in the form of rain. The quantity of rain which falls on particular parts of the globe is very much influenced by the currents of air, and various other causes; but it has been found by extensive experiments, that the same average quantity of rain falls

over the whole earth during the year, and that there is very little variation in the quantity, taking one year with another. This rain, after affording nourishment to the animal and vegetable world, collects through innumerable channels, and in rivers seeks again, by meandering courses, the vast ocean from whence it came. Some philosophers hold the opinion that there are internal subterranean reservoirs of water for supplying the various rivers, and instance the numerous deep springs, salt and boiling springs, and even large rivers, which run for a considerable part of their first course under ground, in support of their theory. But we think the origin and continual supply of rivers may be satisfactorily accounted for from the rains alone. And the phenomena of deep springs and subterranean rivers finds an easy solution in the known laws of hydrostatics.

On the property of water and all fluids finding their level when unobstructed by opposing obstacles depends the phenomena of intermitting springs, and a curious mode of making wells, practised at Modena and Stiria, in Italy.

The workmen dig a deep pit through several strata of soils, until they come to a hard bottom,

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composed of a chalky kind of earth. At this place they begin their mason-work, and build up a circular wall, until they finish it at the top. They now perforate the hard bed of chalk at the bottom, and immediately water flows up and fills the whole well. The springs which supply this water having their origin in a level much above the bottom of the well, whenever an outlet is effected, mount up to the level of their primitive source.

The intermitting spring, again, is caused by a natural syphon formed by a fissure in the earth, as is explained in the following cut:

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de it to be trubasoelect

above. The outlet of this cavity is at its lower part B, which takes the bent direction of the syphon BCD. Whenever the water rises to the level line AC, the spring begins to flow, and will continue to do so till the whole of the water is exhausted, because the level of the outlet D is below the level of the bottom of the reservoir. The water being exhausted, the spring ceases to flow till it again fills to the level of the line AC, and thus it goes on alternately flowing and intermitting.

It was an old opinion, too, that the waters of the ocean were gradually drawn upwards, and filtered through the various porous strata of sand and earth, till they came to the surface of the mountains, from whence they descended again in fresh currents to the sea. But this is altogether an improbable and unsupported fancy.

Rivers commence by a number of small springs or streams uniting to form one current, and this current gradually swelled by tributary waters becomes larger and broader towards its mouth. Rivers, too, run in a more direct channel at their commencement, and become more tortuous and winding as they proceed in their progress. It is an indication to the American savages that they

are approaching towards the sea, when they find the rivers altering their courses, and sweeping in many windings. As these sinuosities increase as the river approaches the sea, it frequently happens that they divide. The Danube runs into the Euxine Sea by seven mouths, the Nile and the Ganges by the same number, and the Wolga by seventy.

What a splendid feature in the scenery of the globe do rivers exhibit!-rising from small and remote sources,-gradually swelling out into mighty currents,-rolling on in perpetual and uninterrupted floods, and pouring their blue and transparent waters through ten thousand different channels, and spreading verdure, and fertility, and gladness on every side! Some rivers intersect continents, and bound the territories of empires. Some take sweeps of thousands of miles, foam over the barriers of mountains, and dive into interminable chasms; others wind beautifully along the calm valley, imparting verdure to the green sloping meadows, and cheering the eye of the shepherd piping on the hills. But the rivers of the New World surpass in magnitude even those of the Old. The river of the Amazons performs a course