Sorata and Illimani. Further to the south, from Valdivia and Chiloë (40° to 429 south latitude), through the Archipelago de los Chonos to Terra del Fuego, we find repeated that singular configuration of fiords (a blending of narrow and deeply indented bays), which, in the Northern Hemisphere, characterises the western shores of Norway and Scotland." (Vol. i, pp. 293-7.)

From the external configuration of continents, considered in reference. to their horizontal expansions, Humboldt proceeds to notice their internal articulation, or the vertical elevation of their soils. "Whatever," he observes, produces a polymorphic diversity of forms on the surface of our planetary habitation-such as mountains, lakes, grassy savannas, or even deserts encircled by a band of forests-impresses some peculiar character on the social condition of the inhabitants." Then a blending of low discontinuous mountain chains and valleys gives rise to various forms of climate, and to an augmented number of vegetable growths; and thus, in a secondary degree, "gives rise to wants that stimulate the activity of the inhabitants."

The analogies and contrasts between the aqueous and aerial envelopes of the solid surface of our planet are then noticed. While the contrasts are chiefly found in the great difference in their conditions of aggregation and elasticity, there are well- marked analogies in the mobility of their particles and in their currents. The rapid decrease of the temperature of the lower strata of the ocean is noticed as a wise arrangement of nature to enable fishes to go down to get a little cool water, in much the same way as in hot weather we seek an elevated region for its coolness. This view has been recently opposed with much vigour by Dr. Williams, of Swansea, who maintains that the extreme pressure must render these cool strata of water altogether unfit for animal existence. There are many points connected with the ocean, more or less fully noticed in these pages, to which we would direct the attention of our readers; but our limited space warns us that we cannot do more than enumerate a few of the most important. Foremost among them we must place the position of the zones of the hottest water, and of that having the greatest saline contents. The waters of the highest temperature appear to form two nearly parallel lines, north and south of the geographical equator. Lenz ascertained that in the Pacific the maxima of density occurred in 22° north, and 17° south latitude, while the minimum was situated a few degrees to the south of the equator. The tides are then considered in a very brief and, we think, unsatisfactory manner; and it is singular that neither in Cotta's Letters, nor in the Translator's notes, is there any reference to the researches of Airy or Whewell. Oceanic currents come in for their due share of attention. Amongst their causes, he observes, we must reckon the period at which tides occur, in their progress round the earth; the duration and intensity of prevailing winds; the modifications of density and specific gravity which the particles of water undergo, in consequence of differences in the temperature, and in the relative quantity of saline contents at different latitudes and depths; and, lastly, the horary variations of the atmospheric pressure, to which we shall presently more specially advert. These currents present the remarkable spectacle of crossing the ocean in various directions, like rivers of uniform breadth, the adjacent strata of water remaining undisturbed, and forming, as it were, the banks of these moving streams. The difference between the moving waters and those at rest is most obvious

where long lines of sea-weed are carried onward by the current, and thus enable us to estimate its velocity.

The general movement of the sea from east to west (the so-called equatorial or rotation current) is supposed to be the result of the joint action of the tidal motion and the trade winds. The velocity of this current, as ascertained by the experiments of Humboldt, and the more recent ones of Daussy, is about ten miles in the twenty-four hours. Christopher Columbus one of the best observers who ever existed, when, during his third voy, age, he was entering the tropics, in the meridian of Teneriffe, wrote in his journal as follows: "I regard it as proved that the waters of the sea move from east to west as do the heavens, that is to say, like the apparent motion of the sun, moon, and stars." He adds, shortly afterwards, that "the movement is strongest in the Caribbean sea," a statement fully borne out by Rennell, who terms this region "not a current, but a sea in motion." The great use of these oceanic rivers is to convey warm water into higher, and cold water into lower latitudes. The great Atlantic gulf stream and its branches are too well known to require any description; our readers may, however, be less familiar with its counterpart, the cold Peruvian stream in the South Pacific, the effect of whose low temperature on the climate of the coast of Chili and Peru was observed by our author in 1802. At certain seasons of the year, the temperature of this cold oceanic current is, within the tropics, only 60°, while the undisturbed adjacent water exhibits a temperature varying from 81° to 84°.

The depth to which these currents of hot and cold water extend has not been ascertained with any degree of precision, but there are reasons for believing that it is very considerable. In connexion with the subject of the temperature of the ocean, we may notice the singular fact first discovered by Franklin, that sand-banks and shoals may be recognised by the coldness of the water over them. Sir Humphrey Davy ascribed this phenomenon to the descent of the particles of water that had been cooled by nocturnal radiation, and which remain nearer to the surface, owing to the hinderance placed in the way of their subsidence; while, according to Humboldt, the depression of temperature depends on the fact that, by the propagation of the motion of the sea, deep waters rise to the margin of the banks, and mix with the upper strata.

Mists are often found over these shoals, owing to the condensation of the vapour of the atmosphere by the cooled waters. These mists often define with sharpness and clearness the form of the shoals below them, appearing as the aerial reflection of the bottom of the sea.

We cannot refrain from transferring to our pages the following exquisitely beautiful passage on the universal diffusion of life throughout the waters of our globe.

"Although the surface of the ocean is less rich in living forms than that of continents, it is not improbable that, on a further investigation of its depths, its interior may be found to possess a greater richness of organic life than any other portion of our planet. Charles Darwin, in the agreeable narrative of his extensive voyages, justly remarks that our forests do not conceal so many animals as the low woody regions of the ocean, where the sea-weed rooted to the bottom of the shoals, and the several branches of fuci loosened by the force of the waves and currents, and swimming free, unfold their delicate foilage upborne by air-cells. The application of the microscope increases, in the most striking manner, our impression of the rich luxuriance of animal life in the ocean, and reveals to the astonished senses a

consciousness of the universality of life. In the oceanic depths, far exceeding the height of our loftiest mountain chains, every stratum of water is animated with polygastric sea worms, cyclid.æ, and orphrydinæ. The waters swarm with countless hosts of small luminiferous, animalcules, mammaria (of the order of acalephæ), crustacea, peridinea, and circling nereides, which, when attracted to the surface by peculiar meteorlogical conditions, convert every wave into a foaming band of flashing light.

"The abundance of these marine animalcules, and the animal matter yielded by their rapid decomposition, are so vast, that the sea water itself becomes a nutrient fluid to many of the larger animals. However much this richness in animated forms, and this multitude of the most various and highly-developed microscopic organisms, may agreeably excite the fancy, the imagination is even more seriously, and I might say more solemnly, moved by the impression of boundlessness and immeasurability, which are presented to the mind by every sea voyage. All who possess an ordinary degree of mental activity, and delight to create to themselves an inner world of thought, must be penetrated with the sublime image of the infinite, when gazing around them on the vast and boundless sea, when involuntarily the glance is attracted to the distant horizon, where air and water blend together, and the stars continually rise and set before the eyes of the mariner. This contemplation of the eternal play of the elements is clouded, like every human joy, by a touch of sadness and of longing." (Vol. i, pp. 314-5.)

But we leave the aqueous for the aerial ocean-the atmosphere surrounding our planet. The full consideration of this subject constitutes the science of meteorology--a science of which our author has been one of the most successful cultivators.

The first point noticed is the chemical constitution of the atmosphere. Its chief constituents are oxygen, nitrogen, carbonic acid, and aqueous vapour. While various circumstances modify the proportions of the two latter, the two former seem invariably to exist in the same ratio to each other. The constancy of this ratio was first ascertained by our author and his friend Gay-Lussac in the year 1804. In twenty-nine experiments made on twenty-nine different days, during the months of November and December, in dry as well as in moist or wet weather, and during different winds, the air of Paris above the surface of the river yielded a per centage of oxygen varying from 212 to 20 9. This difference is so small, as fairly to rank as an error in the experiments. Since the constant composition of 21 of oxygen to 79 of nitrogen was then assigned to the atmosphere by these experimentalists, the accuracy of their results has been confirmed by most of the observers who have followed them.* As the subject is one of the highest interest, we shall notice it somewhat fully. Thirty years after the publication of the researches of Humboldt and Gay-Lussac, De Saussure made numerous experiments (in an entirely different manner) with air collected over the Lake of Geneva, and at Chambeisy. During various winds and different states of weather, the minimum of oxygen was 20-98, and the maximum 2115, the mean being 2105. Similar results have been yielded by air obtained by Gay-Lussac in a balloon. excursion, from a height of 21,430 feet, and by Humboldt, from the Antisana, a mountain 16,640 feet in height. Moreover, there is strong evidence to show that impure air, after the removal and subtraction of its impurities and foreign ingredients, contains oxygen and nitrogen in the same constant ratio. Thus Configliachi examined the air collected over

The numbers 20-8 of oxygen and 792 of nitrogen are given by Boussingault, and may be fairly regarded as representing as accurately as possible the true ratio of the two gases.

rice fields, Seguin, Gay-Lussac, and Humboldt, that from a crowded Parisian theatre, Edmund Davy that from the wards of a hospital, and De Saussure that of bedroom in the morning; and none of these specimens of air showed any variation in the amount of oxygen and nitrogen, the foreign ingredients being previously removed.

On the other hand, there are some trustworthy chemists who maintain that the proportions of oxygen and nitrogen are liable to change within certain limits. Thus Levy found in the air of Guadaloupe, that the dif ference between the maximum and minimum of oxygen in seven experiments amounted to 0:46. Before referring to his explanation of the occasional augmentation of the oxygen, we may mention that M. Doyère has recently attempted to prove that there is a constant alteration in the composition of the atmosphere; or, in other words, that while volumes of air taken from the same flask present identical results, the air taken simultaneously at different places yields results which are too discordant to be regarded as depending on mere errors of manipulation. He has found the oxygen to vary from 20.5 to 215 in 100 parts of air. His assertion has led to a series of experiments instituted during the past year by MM. Regnault and Reiset, who have failed in detecting such marked differences. They analysed air taken from Paris, from its environs, from the south of France, from the sea side, and from Switzerland; and all their results lay between 20-85 and 21.

Levy attempted to refer the cccasional excess of oxygen noticed in his experiments, to its evolution from certain microscopic organisms, and Morren has, to a certain extent, confirmed his views; for he found that air collected on the immediate surface of large ponds of sea-water covering much sea-weed, contained 23 per cent. of its volume of oxygen; and that the minute monads known as the Enchelis momadina virescens sulesphænea of Bory de St. Vincent, mixed with the Enchelis pulvisculus viridis of Müller, and Monas bicolor of Ehrenberg, disengage, when exposed to the sun's rays, very large quantities of this gas. He calculated that from a bulk of water of 8000 cubic feet, containing an abundance of the green matter which was shown by the microscope to consist of the above monads, no less than 128 cubic feet of oxygen were given off in a single day. A similar observation has been made by Wöhler. In the saline springs of Kur-Hesse, a green mucilaginous matter is formed during the summer, from which innumerable air-bubbles are evolved. These bubbles contain 51 per cent. of oxygen and 46 of nitrogen. This green matter consists almost entirely of species of Navicula and Gallionella mixed with fibres of Conferve. This inquiry has been yet further carried on by Morren and Levy in subsequent memoirs; and there can, we think, be no doubt regarding the general correctness of their views. The oxygen thus evolved must, however, so rapidly mix with the surrounding air, as to cause all sensible difference in its ratio almost instantaneously to disappear.

But besides these chief constituents of the atmosphere, it contains "from two to five ten-thousandth parts of carbonic acid gas, a still smaller quantity of carburetted hydrogen gas, and, according to the important experiments of Saussure and Liebig, traces of ammoniacal vapours from which plants derive their nitrogenous contents."

The carbonate of ammonia which has been detected by some observers in the atmosphere, is not dependent on the direct union of the carbonic

acid and the ammoniacal vapour, but seems to be the result of a more complex chemical action. Nitrate of ammonia is occasionally produced under the influence of atmospheric electricity, and, reacting on the carbonate of lime, thus gives rise to carbonate of ammonia.

With regard to the carburetted hydrogen, we are doubtful how far our author is justified in regarding it as a constituent of the atmosphere. That hydrogen and carbon in some form or other, besides that of water and carbonic acid, do exist in the atmosphere, is proved by the experiments of Boussingault, Verver, and others; but nothing has been ascertained, or can be ascertained by those experiments, regarding the state in which they occur. Although the humidity of the atmosphere is noticed as a separate subject in a future page, some reference should have been made to the direct chemical experiments of Ververs and others, in his summary of the ordinary atmospheric constituents. But besides these substances

"There are others accidentally mixed with them, especially near the ground, which sometimes in the form of miasmatic and gaseous contagia, exercise a noxious influence on animal organization. Their chemical nature has not yet been ascertained by direct analysis; but from the consideration of the processes of decay which are perpetually going on in the animal and vegetable substances with which the surface of our planet is covered, and judging from analogies deduced from the domain of pathology, we are led to infer the existence of such noxious local admixtures. Ammoniacal and other nitrogenous vapours, sulphuretted hydrogen gas, and compounds analogous to the polybasic ternary and quarternary combinations of the vegetable kingdom, may produce miasmata, which under various forms may generate ague and typhus fever (not by any means exclusively on wet marshy ground, or on coasts covered by putrescent mollusca and low bushes of Rhizophora mangle and avicennia). Fogs, which have a peculiar smell at some seasons of the year, remind us of these accidental admixtures in the lower strata of the atmosphere. Winds and currents of air caused by the heating of the ground, even carry up to a considerable elevation solid substances reduced to a fine powder. The dust which darkens the air for an extended area and falls on the Cape Verd Islands, to which Darwin has drawn attention, contains, according to Ehrenberg's discovery, a host of siliceous shelled infusoria." (Vol. i, pp. 318-9)

We must, however, proceed to the consideration of other points connected with the atmosphere, and next in order we shall take the variations of atmospheric pressure. It is to the patient and laborious investigations of Humboldt, that we are indebted for our knowledge of the fact of the horary oscillations of the barometer. These oscillations (which, like all diurnally periodic meteorological phenomena, are most simple, and can therefore be best noticed under the equator,) in the tropics present two maxima, viz. at 9 or 9 a. m, and 10 or 102 p. m., and two minima at 4 or 4 p. m. and 4 a. m. (occurring therefore in almost the hottest and coldest hours.) The regularity of these oscillations is so great under the equator, that the hour may be ascertained from the height of the mercurial column, without an error, on an average, of more than fifteen minutes; and this ebb and flow of the ærial ocean is unaffected by storms, hurricanes, rain, and earthquakes. The total amount of a diurnal oscillation amounts to rather more than one tenth of an inch at the equator, and gradually diminishes as the latitude increases. Although we have used the expression" ebb and flow," there is no actual analogy between the causes giving rise to these oscillations and to the oceanic tides; for the phenomena now under consideration is a compound one, resulting from