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the probability that its two arms form one great river higher up its course: and Dr. Krapf has stated that at the point where it joins the Baro, in 9° N. latitude, it is 400 feet broad, with higher banks and a current greater than the Nile. There has certainly been a tradition that the Nile had its origin in a lake, or chain of lakes, at or near the Equator; but, bearing in mind Seneca's description of the sources of the great river- magnus solitudines pervagatus, et in paludes diffusus, gentibus sparsus-it may be that not one but many lakes contribute their overflow to swell the main stream of the Nile; and we are still in total ignorance with respect to one extensive and probably immense division of its basin, viz. the whole of that portion of it which lies to the west. It may be considered as established that the Victoria Nyanza supplies the Nile with a considerable portion of its water; but whether the true and primary source may not yet be found among the high regions which flank the river on both sides of its upper course is still open for geographical inquiry.

The region of the Equator is undoubtedly the source of those abundant rains which supply not only 'the Nile, but many other rivers of Africa, with their periodical floods. It is, as Captain Speke justly says, the centre of atmospheric motion, and there are only two months during the year, in which no rain, or very little, falls. There is, however, a remarkable difference in the phenomena which rivers present under the influence of the periodical rains. If a river flows in a direction parallel to the Equator, its waters spread themselves with a certain degree of equality over the whole extent of its banks, as in the Orinoco, the Senegal, and the Niger; if it flows perpendicularly to the Equator, the effect of the tropical rains is very unequal in different parts of the river's course, for the flood is carried almost entirely towards the lower region of the stream. This is exactly what happens in the inundation of the Nile. No river beyond the torrid zone is subject, like the Nile, to regular periodical swellings. The overflow, which occurs in the temperate zones, arises almost wholly from the melting of snow, and from rain which has fallen among the mountains. In rivers which flow perpendicularly to the Equator, as the swell requires time to travel, it occurs at regular but different periods in various parts of the same river. The height,' Mrs. Somerville says, 'to which the water rises in the annual floods depends upon the nature of the country, but is wonderfully constant in each individual river where the course is long, for the inequalities in the quantity of rain in a district drained by any of its affluents are imperceptible in the general flood;

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and thus the quantity of water carried down is a measure of the mean humidity of the whole country comprised in its basin from year to year. By the admirable arrangement of these periodical inundations, the fresh soil of the mountains, borne down by the water, enriches countries far remote from their source. The Mountains of the Moon and of Abyssinia have thus fertilised the banks of the Nile through a distance of 2500 miles for thousands of years.'

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*

Captain Speke states his belief that the Victoria Nyanza was once much larger than it now is. Undoubtedly a mass of water lying so near to the Equator must be exposed to enormous evaporation; and the more a body of water loses in depth, the more it evaporates, for the evaporation of water is, as is well known, in the direct ratio of its surface, and in the inverse ratio of its depth. There are, in all mountainous and marshy countries, numerous traces of small lakes, which have thus been dried up: we might therefore conclude that the same phenomena have occurred upon a much larger scale in Eastern Equatorial Africa. The Victoria Nyanza, like all lakes, is moreover subject to two agencies which must operate in the course of ages in gradually diminishing its area. The largest deposits of fresh water on the globe, the American lakes, are slowly contracting their dimensions under the joint influence of the enlargement of their barriers by erosion and the accumulation of detritus carried into them by their affluents. It has been generally supposed that no lake can have more than one outlet; but if Captain Speke's observations are correct, the Victoria Nyanza presents the peculiarity of at least three outlets at distances respectively of from thirty to forty miles from each other, thus forming, as it were, a reversed delta. It has been assumed that the perpetual wearing away of the banks of an outlet prevents the formation of others. Instances, however, have been recently adduced proving that the Victoria Nyanza is not singular in possessing two or more outlets. The Lake of St. John, in Lower Canada, discharges itself, it is said, by three outlets into the River Saguenay, first by two branches called the Grande Décharge,' and next by a chain of alternate rivers and lakes which join the main stream after a course of fifty miles. An example on a small scale has also been adduced of a Scotch loch possessing two natural outlets. There appears, therefore, to be nothing inconsistent with hydrographical experience in the fact of two or more rivers issuing from the Victoria

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* Physical Geography,' vol. ii.

† See Athenæum for July 18, Nov. 28, and Dec. 19, 1863.

Nyanza.

Nyanza. The tendency, however, of vast and shallow lakes, swollen by periodical rains, is to subside during the dry season into temporary marshes, and the surface of the Victoria Nyanza must be subject to considerable annual oscillations; it would therefore be both interesting and important to ascertain the effect of those oscillations upon the stream of the effluent which descends the Ripon Falls.

We possess, however, incontrovertible proof that the periodical rains of Upper Ethiopia have not varied for at least 5000 years. Sirius, the dog star, was worshipped by the Egyptians from its supposed influence on the rising of the Nile. According to Champollion, their calendar commenced when the heliacal rising of the star coincided with the summer solstice, the time at which the Nile began to swell at Cairo. Now, this coincidence,' Mrs. Somerville says, 'makes, with the nearest approach to accuracy, 3291 years before the Christian era; and as the rising of the river still takes place precisely at the same time, and in the same manner, it follows that the quantity of rain which falls in the basin of the Nile has not varied for 5000 years.' This basin occupies, it has been estimated, an area of at least 500,000 square miles. The cause of the retardation of the inundation is not yet accurately known, but the inundation itself can be satisfactorily explained, as has been frequently pointed out, by the annual overflow of a vast interior watery plateau, the exact configuration and limits of which yet remain to be ascertained. Many large, and doubtless innumerable smaller, streams pour their tributary floods into the Nile. Many of these streams are probably feeders of the Victoria Nyanza; but as almost the whole of that lake lies south of the Equator, it must be subjected to conditions with respect to rainfall different from those of the country to the north, from which the principal supplies of the Nile are in all probability derived.

The rains commence at Kazé, 5° S. lat., about the 15th of November, and end on the 15th of May, during which period they fall almost continuously. About 21° farther north, at the southern end of the Victoria Nyanza, the rainy season commences somewhat later. At Karagué, upon the western shore of the lake, the rainy season lasts from October to June, when the dry season sets in. The altitude of the Nyanza, and the argillaceous colour and the sweetness of its waters, suggest the inference, Captain Burton says, that it may be one of the feeders of the Nile; and it may be right to quote his reasons for thinking that it is not the chief source of the annual inundation, and therefore not of the Nile itself. 'About the summer solstice,' he says, 'when the rains cease in the regions south of and upon the Equator, the

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White Nile begins to flood. From March to the autumnal equinox (September) it continues to overflow its banks till it attains its greatest magnitude, and from that time it shrinks through the winter solstice (December) till March. The Nile is therefore full during the dry season, and low during the rainy season south of, and immediately upon, the Equator. The inundation is synchronous with the great falls of the Northern Equatorial Regions, which extend from July to September, and is dependent solely on tropical rains. It is therefore probable that the true sources of the "Holy River" will be found to be a network of runnels and rivulets of scanty dimensions, filled by monsoon torrents, and perhaps a little swollen by melted snow on the northern parting line of the Eastern Lunar Mountains.'* 'In the map appended to M. Brun Rollet's volume,' Captain Burton adds, the large water to the west of the Padongo tribe, which clearly represents the Nyanza, is made to drain northwards into the Filtri Lake, and eventually to swell the main stream of the White River. The detail supplied by the Egyptian Expedition, which about twenty years ago ascended the White River to 3° 22' N. lat. and 31° 30' E. long., and gave the general bearing of the river from that point to its source as south-east, with a distance of one month's journey or from 300 to 350 miles, would place the actual sources 2° s. lat. and 35° E. long. or in 2° eastward of the southern creek of the Nyanza Lake. This position would occupy the northern slope of the Lunar Mountains, the upper watershed of the high region whose culminating apices are Kilimandjaro, Kenia, and Daemgo Engai, the first supposed to be at least 21,000 feet above the level of the sea, and consequently 3000 or 4000 feet above the line of perpetual congelation, and would admirably explain the two most ancient theories concerning the source of the White River; namely, that it rises in a snowy region, but its inundation is the result of tropical rains.'

We have little or no exact information as to the amount and duration of the rainfall in the region of the Victoria Nyanza, but Captain Speke incidentally supplies a fact which may be thought to strongly corroborate the hypothesis of his former companion, in reference to the flooding of the Nile. The great rush-drains or rivers which Captain Speke crossed on his route to Mtesa's palace were, he was told by the natives, at certain seasons so flooded that they could not be forded, but, from some unaccountable cause, they were always lowest when most rain fell in Uganda;-a conclusive proof, we think, that the Victoria

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*Lake Regions of Central Africa,' vol. ii. p. 218.

Nyanza

Nyanza must receive its chief supply of water from the regions far to the south of the Equator, and is consequently fullest at a time when very little rain falls in the regions to the north from which the Nile necessarily derives the largest portion of its flood.

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The periodical rise of the Nile is certainly not, in any considerable degree, owing to the melting of the snow on those mountains which have now been ascertained to exist at no great distance from the Equator in Eastern Intertropical Africa ; for the power of the sun is there so nearly equable throughout the year that it must operate in supplying the streams which descend from those mountains with nearly the same amount of water at all seasons. There has been a constant tradition that the mountains in the vicinity of the head waters of the Nile are covered with perpetual snow. Ptolemy repeatedly alludes to the fact. Philostratus says that 'he does not mean to gainsay the snows of the Ethiopians on the hills of the Catadupi.' Bruce often heard of the snowy regions in the vicinity of the Equator. The missionaries Rebmann and Krapf were the first Europeans who saw these stupendous mountains, and their existence has since been indisputably established by the partial ascent of the great Kilimandjaro by the Baron von Decken. The pertinacity with which the fact of mountains in Eastern Equatorial Africa being crowned with perpetual snow has been denied is unaccountable. Unless it is now intended to impugn the veracity, or to question the powers of scientific observation, of a Hanoverian nobleman and officer of high attainments, the question must be considered as settled, for there cannot remain a scintilla of doubt in any unprejudiced mind on this most interesting subject. Why there should have been any is not easy to understand, for the limit of perpetual snow is not a mere function of geographical latitude nor of mean annual temperature. In the Andes of Quito, directly under the Equator, the limit is 15,790 feet above the sea. On the southern declivities of the Himalaya the snow limit is found at an elevation of 12,180 feet, and on the northern declivity at 15,000 feet. Neither the tropics, nor even the Equator itself, is the situation, as was long believed and taught, where the snow limit attains its highest elevation. The phenomenon,' says Humboldt, 'is an extremely complicated one, and depends generally on various relations of temperature, moisture, and mountain configuration. While the snow line in South America reaches a height under the Equator which equals that of the summit of Mont Blanc, and

* See Rawlinson's ' Herodotus,' vol. ii. p. 27.

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