at the surface, and it would soon die if kept immersed ; if it be removed, and the water poured from the height of two or three feet, from one vessel to another, for a few minutes, upon then immersing the fish it will not show such signs of distress as at first.

The water, on the one hand, contained no air for exciting the action of the respiratory organs of the fish, it therefore gasped to obtain a supply from the external atmosphere; but, on the other hand, by pouring the water for a time from one vessel to another, it became aërated, and fitted to yield a supply to the fish when introduced.

Fishes breathe in consequence of their respiratory organs being fitted to withdraw oxygen, not from the water itself, but from the air, that it is capable of dissolving and of holding in solution under ordinary circumstances.

The chemist applies these facts to the explanation of a natural phenomenon ;-let us suppose that the unaërated, unproductive water of the lake overflows its bounds, and under the influence of gravitation dashes as a cataract over the mountain side; each moment that it increases in velocity, it passes into denser and denser regions of the atmosphere, and in the hurry and turbulence of its fall, dissolves air, foams with bubbles, and then flows onwards and throughout the vallies and plains, as a stream or river, sufficiently aërated for supporting the respiration of aquatic beings, and accordingly we now find them in abundance.

The description of this beautiful phenomenon may be aided by reference to the engraving, in which the horizontal shading being strong below, faint in the centre, and faintest at the top, may denote as at page 122, that the atmosphere is heavy upon the level surface of the earth, light at some height above, and lightest at the elevation of the mountain summit.

Upon this, the unaërated water of the lake is supposed to be; and as it overflows and falls through the successive strata of the atmosphere, as indicated by the successive increase of the shading, it gains more and more air, until upon its arrival in the heaviest air, as indicated by the strongest shading, at the base of the mountain it becomes turbulent with foam.

The grandeur of a mountain torrent, cataract, or waterfall, is chiefly referrible to the tremendous velocity of its fall in the denser regions of the air, and the powerful shock with which the water and air incorporate, producing an enormous foam,

As such water traverses the surface of the earth in its return to the parent ocean, it widens its course and thus exposing a larger surface to the atmosphere, becomes more powerfully aërated, and likewise by the rippling, the agitation, into which it is thrown by breezes and winds.

If we fill a vessel with water, thus naturally and wonderfully aërated, and place a fish in it, and then secure the mouth of the vessel with an air-tight cover, the creature will die when its respiration has consumed the certain amount of oxygen that the air contained ; it will die though immersed in water that contains oxygen as an element, but this is combined with hydrogen, be it remembered, and the respiratory organs of the fish have not the power of separating it from such chemical combination, as they have from its mechanical mixture with nitrogen, which constitutes the chief volume of atmospheric air.

Fishes demand a constant supply of fresh aërated water, the same as animals demand a constant supply of fresh hydrated air, for both classes of beings are soon destroyed by the mephitic products of their own respiration.

The lavish abundance of air and water presented throughout Nature, would alone probably ensure the

fulfilment of these demands for oxygen, and ages might elapse before either of these extraordinary media would become vitiated, or unfitted for the maintenance of life; but the Creator has made the same beneficent provision for purifying water from the results of the respiration of aquatic beings, as He has made for purifying air from those of man and the higher order of animals.

Everything is miraculously balanced and adjusted throughout the Creation, and displays the power and goodness of God; and above all branches of science, that of chemistry is particularly favoured in being permitted to become the medium of interpreting so many wonders.

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During the bright weather of Summer and Autumn most plants that grow in ponds, pools, and streams, and particularly those slender green filaments known to the botanist as conferva rivularis," are covered with myriads of small air globules; this is a common "observation ;"-the chemist devises means of collecting thousands of these globules in a glass, and finds that such aëriform volume will cause a lighted taper to burn with far greater brilliancy than it burns in the surrounding atmosphere: this is a simple "experiment;" he next reasons upon this, and guided by" analogy" tries if all plants of a similar character, when exposed to light, will present the same phenomenon; he finds them to do so, and thus establishes a "scientific truth."

These three essential requisites enabled us to recog

nize the plants of the earth, combining their agencies for purifying the atmosphere from the mephitic results of combustion, and the respiration of man, and the higher order of animals; they will now enable us to recognize the plants of the water, combining their agencies for purifying it from the mephitic results of the respiration of fishes, and other aquatic beings.

When under the direct influence of solar light, the slender green filaments of "conferve" have the power of decomposing the carbonic acid, produced by the respiration of fishes, and of eliciting oxygen nearly pure; thus globules of this element, ascending and collecting in the glass, will support the flame of a taper with greater brilliancy than the surrounding atmosphere containing nitrogen.

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Two or three handfuls of "conferva rivularis" collected carefully without injuring their fragile structure, may be introduced into a large globular glass " carafe," or water-flagon," having a long and narrow neck— the narrower the better; then fill the carafe with water from the pool, pond, or stream, in which the plant grew, place one hand over the mouth of the "carafe" to close it firmly, and with the other holding the globular part, invert it; pass the first hand beneath the surface of three or four pints of water contained in a shallow pan or glass, then withdraw it from the neck of the carafe;" no water will escape from this, because the weight of such water is inferior to that of the surrounding atmosphere; thus the "carafe" will