to the idea of a chemical solution; and this idea is no way at variance with the phenomena, that we daily observe in our laboratories. The waters of great rivers contain carbonic acid; and, were they even entirely pure, they would still be capable, in very great volumes, of dissolving some portions of oxyd, or those metallic hydrats, which are regarded as the least soluble. The mud of the Nile, which is the sediment of the matters that the river holds suspended, is destitute of manganese; but contains, according to the analysis of Mr Regnault, six parts in a hundred of oxyd of iron; and its colour, at first black, chan ges to yellowish brown by desiccation and the contact of air. The mud consequently

is not the cause of the black crusts on the rocks of Syene. Mr Berzelius had the goodness, at my request, to examine these crusts, and recognized in them, as in those of the granites of the Oroonoko and Rio Congo, the union of iron and manganese. This celebrated chemist thinks, that the rivers do not take up these oxyds from the soil over which they flow, but derive them from their subterraneous sources, and deposit them on the rocks in the manner of cementation, by the action of particular affinities, perhaps by that of the potash of the feldspar. A long residence at the cataracts of the Oroonoko, the Nile, and the Rio Congo, and an examination of the circumstances that accompany this phenomenon of coloration, could alone lead to the complete solution of the problem we have discussed. Is this phenomenon independent

of the nature of the rocks? I shall content myself with observing in general, that neither the granitic masses remote from the ancient bed of the Oroonoko, but exposed during the rainy season to the alternations of heat and moisture, nor the granitic rocks bathed by the brownish waters of the Rio Negro, assume the appearance of meteoric stones. The Indians say, that the rocks are black only where the waters are white. They ought perhaps to add, where the waters acquire great swiftness, and strike with force against the rocks of the banks.' Cementation seems to explain why the crusts augment so little in thickness."

pp. 20-24.

The next speculation relates to a fact which has long been known to those who dwell in the neighbourhood of falls of water, and which has often been accounted for on principles which our author controverts. The fact is, that the noise of a cataract is commonly prodigiously increased in intensity during the night. The principles which naturally suggest themselves as accounting for this fact are, in the first place, the increased stillness of the air during the night, when every

sound of living thing is hushed, and nature, therefore, seems to utter a louder voice, only because no discordant sound mingles with her echoes; and in the next place, it is supposed that the moisture and coolness of the air during night are still more efficient causes of this phenomenon-and this is the solution which even philosophic minds have been accustomed to give. Let us now hear Mr Humboldt on the fact; and without presuming to answer for the justness of his theory, we shall at least be forced to confess that it is ingenious and plausible.

"The inhabitants of Atures and Maypures, whatever the missionaries may have asserted in their works, are not more struck with deafness by the noise of the great cataracts, than the Catadupes of the Nile. When this noise is heard in the plain that surrounds the mission, at the distance of more than a league, you seem to be near a coast skirted by reefs and breakers. The noise is three times as loud by night as by day, and gives an inexpressible charm to these solitary scenes.

What can be the cause of this increased intensity of sound in a desert, where nothing seems to interrupt the silence of nature? The velocity of the propagation of sound, far from augmenting, decreases with the lowering of the temperature. The intensity diminishes in air agitated by a wind, which is contrary to the direction of the sound; it diminishes also by dilatation of the air, and is weaker in the higher than in the lower regions of the atmosphere, where the number of particles of air in motion is greater in the same radius. The intensity is the same in dry air, and in air mingled with vapours; but it is feebler in carbonic acid gas, than in mixtures of azote and oxygen. From these facts, which are all we know with any certainty, it is difficult to explain a phenomenon observed near every cascade in Europe, and which, long before our arrival in the village of Atures, had struck the missionary and the Indians. The nocturnal temperature of the atmosphere is 3o less than the temperature of the day; at the same time the apparent humidity augments at night, and the mist that covers the cataracts becomes thicker. We have just seen, that the hygroscopic state of the air has no influence on the propagation of the sound, and that the cooling of the air

diminishes its swiftness.

"It may be thought, that, even in places not inhabited by man, the hum of insects, the song of birds, the rustling of leaves agitated by the feeblest winds, occasion during the day a confused noise, which we perceive the less because it is uniform, and constantly strikes the ear. Now this

noise, however slightly perceptible it may be, may diminish the intensity of a louder noise; and this diminution may cease, if during the calm of the night the song of birds, the hum of insects, and the action of the wind upon the leaves, be interrupted. But this reasoning, even admitting its justness, can scarcely be applied to the forests of the Oroonoko, where the air is constantly filled by an innumerable quantity of moschettoes, where the hum of insects is much louder by night than by day, and where the breeze, if ever it be felt, blows only after sunset.

"I rather think, that the presence of the sun acts upon the propagation and intensity of the sound by the obstacles, which they find in the currents of air of different density, and the partial undulations of the atmosphere caused by the unequal heating of different parts of the soil. In calm air, whether it be dry, or mingled with vesicular vapours equally distributed, the sonorous undulation is propagated without difficulty. But when the air is crossed in every direction by small currents of hotter air,

the sonorous undulation is divided into two

undulations, where the density of the medium changes abruptly; partial echoes are formed, that weaken the sound, because one of the streams comes back upon itself; and those divisions of undulations take place, of which Mr Poisson has recently developed the theory with great sagacity. It is not therefore the movement of the particles of air from below to ahove in the ascending current, or the small oblique currents, that we consider as opposing by a shock the propagation of the sonorous undulations. A shock, given to the surface of a liquid, will form circles around the centre of percussion, even when the liquid is agi. tated. Several kinds of undulations may cross each other in water, as in air, without being disturbed in their propagation; little movements may ride over each other, and the real cause of the less intensity of sound during the day appears to be the interrup. tion of homogeneity in the elastic medium. During the day, there is a sudden interruption of density, wherever small streamlets of air of a high temperature rise over parts of the soil unequally heated. The sonorous undulations are divided, as the rays of light are refracted, and form the mirage (looming) wherever strata of air of unequal density are contiguous. The propagation of sound is altered, when a stratum of hydrogen gas is made to rise in a tube closed at one end above a stratum of atmospheric air; and Mr Biot has well explained by the interposition of bubbles of carbonic acid gas, why a glass filled with Champagne wine is little sonorous so long as the gas is evolved, and continues to pass through the strata of the liquid.

"În announcing these ideas, I might

almost rest on the authority of an ancient philosopher, whom the moderns continue to treat with disdain, though the most distinguished zoologists have long rendered ample justice to the sagacity of his observations. Why,' says Aristotle in his curious book of Problems, why is sound better heard during the night? Because there is more calmness on account of the absence of caloric, (of the hottest.) This absence renders every thing calmer, for the sun is the principle of all movement.", Aristotle had no doubt a vague presentiment of the cause of the phenomenon ; but he attributes to the motion of the atmosphere, and the shock of the particles of air, what seems to be rather owing to abrupt changes of density in the contiguous strata of air.” pp. 67–72.

The scenery of the Oroonoko seems, from the descriptions of our traveller, to be often in the highest degree impressive and sublime, and its cataracts have a character of majesty and of continuous grandeur which is not presented by similar rivers in any other quarter of the globe. The following description of the cataract of Maypures, and also of the general character of tropical scenery, is exceedingly striking.

"To take in at one view the grand character of these stupendous scenes, the spectator must be stationed on the little mountain of Manimi, a granitic ridge, that rises from the Savannah, north of the church of the mission, and is itself only a continuation of the steps, of which the raudalito of Manimi is composed. We often visited this mountain, for we were never weary of the view of this astonishing spectacle, concealed in one of the most remote corners of the earth. Arrived at the summit of the rock, the eye suddenly takes in a sheet of foam, extending a whole mile. Enormous masses of stone, black as iron, issue from its bosom. Some are paps grouped in pairs, like basaltic hills; others resemble towers, strong castles, and ruined buildings. Their gloomy tint contrasts with the silvery splendour of the foam. Every rock, every islet is covered with vigorous trees, collected in clusters. At the foot of those paps, as far as the eye can reach, a thick vapour is suspended over the river, and through this whitish fog the tops of the lofty palm-trees shoot up. What name shall we give to these majestic plants? I suppose them to be the vadgiaï, a new species of the genus oreodoxa, the trunk of which is more than eighty feet high. The leafy plume of this palm-tree had a brilliant lustre, and rises almost straight toward the sky. At every hour of the day

the sheet of foam displays different aspects. Sometimes the hilly islands and the palmtrees project their broad shadows, some times the rays of the setting sun are refracted in the humid cloud, that shrouds the cataract. Coloured ares are formed, and vanish and appear again alternately; light sport of the air, their images wave above the plain.

"Such is the character of the landscape discovered from the top of the mountain of Manimi, which no traveller has yet described. I do not hesitate to repeat, that neither time, nor the view of the Cordille

ras, nor any abode in the temperate vallies of Mexico, have effaced from my mind the powerful impression of the aspect of the cataracts. When I read a description of those places in India, that are embellished by running waters and a vigorous vegetation, my imagination retraces a sea of foam and palm-trees, the tops of which rise above a stratum of vapour. The majestic scenes of nature, like the sublime works of poetry and the arts, leave remembrances that are incessantly awakening, and through the whole of life mingle with all our feelings of what is grand and beautiful.

The calm of the atmosphere, and the tumultuous movement of the waters, produce a contrast peculiar to this zone. Here no breath of wind ever agitates the foliage, no cloud veils the splendour of the azure vault of Heaven; a great mass of light is diffused in the air, or the earth strewn with plants with glossy leaves, and on the bed of the river, which extends far as the eye can reach. This appearance surprises the traveller born in the north of Europe. The idea of wild scenery, of a torrent rushing from rock to rock, is linked in his imagination with that of a climate, where the noise of the tempest is mingled with the sound of the cataracts; and where, in a gloomy and misty day, sweeping clouds seem to descend into the valley, and rest upon the tops of the pines. The landscape of the tropics in the low regions of the continents has a peculiar physiognomy, something of greatness and repose, which it preserves even where one of the elements is struggling with invincible obstacles. Near the equator, hurricanes and tempests belong to islands only, to deserts destitute of plants, and to those spots, where parts of the atmosphere repose upon surfaces, from which the radiation of heat is very different." pp. 137-140.

We have of late been much pleased with the sober cast which many speculations have assumed, that but a few years ago were remarkable only for extravagance. It was then, and had been for ages, a favourite theory to account for the very various appearances of vegetation and of animal

VOL. IX.

forms in different hemispheres and in remote countries, by referring all of them to varieties of climate and of soil; although these varieties are often so great as to be very inadequately ac counted for upon this principle. Those who love what is sound in philosophy, will therefore be pleased with the following most just observations.

"Every hemisphere produces plants of a different species; and it is not by the diversity of climates that we can attempt to explain why equinoctial Africa has no laurineæ, and the New World no heaths; why the calceolaria are found only in the southern hemisphere; why the birds of the continent of India glow with colours less splendid than the birds of the hot parts of America; finally, why the tiger is peculiar to Asia, and the ornithorhincus to New Holland. In the vegetable as well as in the animal kingdom, the causes of the distriber of mysteries, which natural philosophy bution of the species are among the num

cannot reach. This science is not occu

pied in the investigation of the origin of they are distributed on the globe. It exbeings, but of the laws according to which amines the things that are, the co-existlatitude, at different heights, and at difference of vegetable and animal forms in each ent degrees of temperature; it studies the relations under which particular organizations are more vigorously developed, multiplied, or modified; but it approaches possible, since they touch the origin, the not problems, the solution of which is imadd, that the attempts which have been first existence of a germe of life. We may made, to explain the distribution of various species on the globe by the sole influence of climate, date at a period when physical geography was still in its infancy; when, recurring incessantly to pretended contrasts between the two worlds, it was

imagined, that the whole of Africa and of America resembled the deserts of Egypt and the marshes of Cayenne. At present, when men judge of the state of things not positive knowledge, it is ascertained, that from one type arbitrarily chosen, but frora

the two continents in their immense extent contain countries that are altogether analogous. There are regions of America as barren and burning as the interior of Africa. The islands that produce the their dryness; and it is not on account of spices of India are scarcely remarkable for

the humidity of the climate, as it has been affirmed in recent works, that the New

Continent is deprived of those fine species of laurinee and myristica, which are found united in one little corner of the earth in the Archipelago of India. For some years past the real cinnamon has been cultivated

green. Several lakes of Savoy and of Peru have a brown colour approaching black. Most of these phenomena of coloration are observed in waters that are believed to be the purest, and it is rather from reasonings founded on analogy, than from any direct analysis, that we may throw some light on so uncertain a matter. In the vast system of rivers which we have traversed, (and this fact appears to me striking,) the black waters are principally restricted to the equatorial band. They begin to be found about five degrees of north latitude; and abound thence to beyond the equator as far as about two degrees of south latitude. The mouth of the Rio Negro is indeed in the latitude of 3° 9'; but in this interval the black and white waters are so singularly mingled in the forests and the savannahs, that we know not to what cause the coloration of the waters must be attributed. The waters of the Cassiquiare, which fall into the Rio Negro, are as white as those of the Oroonoko, from which it issues. Of two tributary streams of the Cassiquiare very near each other, the Siapa and the Pacimony, one is white, the other black.

"When the Indians are interrogated respecting the causes of these strange colorations, they answer, as questions in natural philosophy or physiology are sometimes answered in Europe, by repeating the fact in other terms. If you address yourself to the missionaries, they reply, as if they had the most convincing proofs of their assertion, the waters are coloured by washing the roots of the sarsaparilla." The smilaceæ, no doubt, abound on the banks of the Rio Negro, the Pacimony, and the Cababury; their roots, macerated in the water, yield an extractive matter, that is brown, bitter, and mucilaginous; but how many tufts of smilax have we seen in places, where the waters were entirely white! In the marshy forest which we traversed, to convey our canoe from the Rio Tuamini to the Canno Pimichin and the Rio Negro, why, in the same soil, did we ford alternately rivulets of black and white water? Why was no river ever found white near its springs, and black in the lower part of its course? I know not whether the Rio Negro preserve its yellow ish brown colour as far as its mouth, notwithstanding the great quantity of white water it receives from the Cassiquiare and the Rio Blanco. Mr. de la Condamine, not having seen this river north of the equator, could not judge of the difference of colour.

"Although, on account of the abundance of the rivers, vegetation is more vigorous close to the equator than eight or ten degrees north or south, it cannot be affirmed, that the rivers with black waters rise principally in the most shady and thickest forests. On the contrary, a great number of the aguas negras come from the

ceæ.

open savannahs, that extend from the Meta beyond the Guaviare toward the Caqueta. In a voyage which I made with "Mr de Montufar from the port of Guayaquil to Bodegas de Babaojo, at the period of the great inundations; I was struck by the analogy of colour displayed by the vast savannahs of the Invernadero del Garzal and of Lagartero, and the aspect of the Rio Negro and the Atabapo. These savannahs, partly inundated during three months, are composed of paspalum, eriochloa, and several species of cyperaWe sailed on waters that were from four to five feet deep; their temperature was by day from 33° to 34° of the centigrade thermometer; they exhaled a strong smell of sulphuretted hydrogen, to which, no doubt, some rotten plant of arum and heliconia, that swam on the surface of the pools, contributed. The waters of Lagartero were of a golden yellow by transmitted, and coffee brown by reflected light. They are, no doubt, coloured by a carburet of hydrogen. An analogous phenomenon is observed in the dunghill waters prepared by our gardeners, and in the waters that issue from bogs. May we not also admit, that it is a mixture of carbon and hydrogen, an extractive vegetable matter, that colours the black rivers, the Atabapo, the Zama, the Mataveni, and the Guainia? The frequency of the equatorial rivers contributes, no doubt, to this coloration, by filtrations through a thick wad of grasses. I suggest these ideas only in the form of a doubt. The colouring principle seems to be in very little abundance; for I observed, that the waters of the Guainia or Rio Ne. gro, when subjected to ebullition, do not become brown like other fluids charged with carburets of hydrogen."

pp. 185-191.

The following relation is of a very different kind from any we have yet quoted, and gives an affecting picture both of the miseries of savage life, and of the power of those natural instincts which bind the heart of woman to the children which she has born. Speaking of his passage up one of the rivers, our traveller thus proceeds.

"Before we reached its confluence, a granitic hummock, that rises on the western bank, near the mouth of the Guasacavi, fixed our attention; it is called the Rock of the Guahiba Woman, or the Rock of the Mother, Piedra de la Madre. We inquired the cause of so singular a denomination. Father Zea could not satisfy our curiosity; but some weeks after, another missionary, one of the predecessors of this ecclesiastic, whom we found settled at San Fernando as president of the missions, related to us an event, which I recorded in