I have recorded with care and attention the information which I have collected regarding the Indus and its tributaries; yet the magnitude of that river must be decided by a comparison with the other great rivers of the world. An European, in the East, may appropriately narrow his field, and confine such a comparison to its great twin river, the Ganges, which, with the Indus, folds, as it were, in the embrace our mighty empire of British India. At this time, too, in a publication which has appeared at Calcutta, by Mr. G. A. Prinsep, regarding the introduction of steam navigation into India, we have late and valuable matter, both of an interesting and scientific nature, regarding the peculiarities of the Ganges; which, with the previous papers of Rennell and Colebrooke, afford very precise information regarding that river. I have ventured, therefore, however incompetent, to lay down the observations that have occurred to me regarding the Indus, that the requisite comparison might be instituted.

The Ganges and Indus, rising in the same mountains, traverse, with an unequal length of course, the same latitudes: both rivers, though nearly excluded from the tropics, are yet subject to be annually flooded at a stated and the same period. The quantity of water, therefore, which these rivers respectively discharge, will determine their relative size; and we shall afterwards consider the slope or fall by which they descend to the ocean. Sicriguli, on the Ganges, and Tatta, on the Indus, seem to be the preferable sites for drawing a comparison, since both places are situated at a point before the rivers have subdivided to form a delta, and after they have each received the whole of their tributary streams. The Indus certainly throws off two branches above Tatta, the Fulailee and Pinyaree; but they are only considerable rivers in the rainy season.

It appears, then, from Mr. G. A. Prinsep’s essay, that in the month of April the Ganges discharges, at Sicriguli, about 21,500 cubic feet of water in a second. The average breadth of the river at that place is given at 5000 feet, which is also the velocity in a second of time; while its average depth does not exceed three feet. That in this result we form a pretty correct estimate of the magnitude of the Ganges, is further proved by the state of the river at Benares in the same month (April), where, though contracted to a breadth of 1400 feet, the depth exceeds thirty-four feet, and the discharge amounts to 20,000 cubic feet per second, which differs in but a trifling degree from that at Sicriguli.

In the middle of April, I found the Indus at Tatta to have a breadth of 670 yards, and to be running with a velocity of two miles and a half an hour. It happens that the banks are steep on both sides of the river in this part of its course; so that the soundings, which amount to fifteen feet, are regular from shore to shore, if we except a few yards on either side, where the water is still. This data would give a discharge of 110,500 cubic feet per second; but by Buat’s equations for the diminished velocity of the stream near the bed, compared with that of the surface, it would be decreased to 93,465 cubic feet. Some further deduction should be made for the diminished depth towards the shores; and 80,000 cubic feet per second may be taken as a fair rate of discharge of the Indus in the month of April.[17] It is a source of regret to me that I am unable to extend my observations to the river during the rainy season; but I had not an opportunity of seeing it at that period, and do not desire to place opinion in opposition to fact. I may mention, however, that at Sehwun, where the Indus is 500 yards wide, and thirty-six feet deep, and sweeping with great velocity the base of a rocky buttress that juts in upon the stream, there is a mark on the precipice which indicates a rise of twelve feet during the inundation. This gives a depth of eight fathoms to this part of the Indus in the rainy season. If I could add the increase of width on as sound data as I have given the perpendicular rise or depth of water, we should be able to determine the ratio between its discharge at the opposite seasons; but I have only the vague testimony of the natives to guide me, and dismiss the subject.

From what has been above stated, it will be seen that the Indus, in discharging the enormous volume, of 80,000 cubic feet of water in a second, exceeds by four times the size of the Ganges in the dry season, and nearly equals the great American river, the Mississippi. The much greater length of course in the Indus and its tributaries, among towering and snowy mountains near its source, that must always contribute vast quantities of water, might have prepared us for the result; and it is not extraordinary, when we reflect on the wide area embraced by some of these minor rivers, and the lofty and elevated position from which they take their rise: the Sutledge, in particular, flows from the sacred Lake of Mansurour, in Tibet, 17,000 feet above the sea. The Indus traverses, too, a comparatively barren and deserted country, thinly peopled and poorly cultivated; while the Ganges expends its waters in irrigation, and blesses the inhabitants of its banks with rich and exuberant crops. The Indus, even in the season of inundation, is confined to its bed by steeper and more consistent banks than the other river; and, as I have stated, seldom exceeds half a mile in width: the Ganges, on the other hand, is described as an inland sea in some parts of its course; so that, at times, the one bank is scarcely visible from the other,—a circumstance which must greatly increase the evaporation. The arid and sandy nature of the countries that border the Indus soon swallow up the overflowing waters, and make the river more speedily retire to its bed. Moreover, the Ganges and its subsidiary rivers derive their supply from the southern face of the great Himalaya; while the Indus receives the torrents of either side of that massy chain, and is further swollen by the showers of Cabool and the rains and snow of Chinese Tartary. Its waters are augmented long before the rainy season has arrived; and, when we look at the distant source of the river, to what cause can we attribute this early inundation but to melting snow and ice?

The slope on which the Indus descends to the ocean would appear to be gentle, like that of most great rivers. The average rate of its current does not exceed two miles and a half an hour; while the whole of the Punjab rivers, which we navigated on the voyage at Lahore, were found to be one full mile in excess of the Indus. We readily account for this increased velocity by their proximity to the mountains; and it will serve as a guide in estimating the fall of the river. The city of Lahore stands at a distance of about 1000 British miles from the sea, by the course of the river; and I am indebted to Dr. J. G. Gerard, for a series of barometrical observations, made some years ago at Umritsir, a city about thirty miles eastward of Lahore.

I am informed that the height of the instrument registered in Calcutta may be twenty-five feet above the level of the sea; and as the city of Umritsir is about the same level as Lahore (since both stand on the plains of the Punjab), it must have an elevation of about 900 feet from the sea.

Having now stated the sum of our knowledge regarding this subject, it remains to be considered in what, and how great a proportion, the slope is to be distributed among the rivers from Lahore downwards. By a comparison with the Ganges in Rennell’s work, and the late treatise to which I have alluded, and assisted by the same scientific gentleman, to whom I have before expressed my obligations, we cannot give a greater fall downwards from Mittun, where the Indus receives the Punjab rivers, than six, or perhaps five, inches per mile: nor can we allow more than one fourth of 900 feet as the height of that place above the level of the sea; for the river has not increased here in velocity of current, though we have neared the mountains. Mittun is half way to Lahore, about 500 miles from the sea, and nearly 220 feet above it. The remaining 680 feet we may fairly apportion to the Punjab rivers, from their greater rapidity of course; which would give them a fall of twelve inches per mile.

In these facts, we have additional proof of the greater bulk of the Indus, as compared with the Ganges; when at the lowest, it retains a velocity of two and a half miles, with a medial depth of fifteen feet, and though running on as great, if not a greater slope than that river, never empties itself in an equal degree, though much more straight in its course. The Indus has none of those ledges, which have been lately discovered as a peculiarity of the Ganges, and which are described in Mr. Prinsep’s work as “making the bed of that river consist of a series of pools, separated by shallows or sand-bars, at the crossing of every reach.” Were the Indus as scantily supplied with water as the Ganges, we should, doubtless, find a similar state of things; and, though the bed of the one river would appear to far exceed in magnitude that of the other, we find the Ganges partaking much of the nature of a hill-torrent, overflowing at one season, insignificant at another; while the Indus rolls on throughout the year, in one majestic body, to the Ocean.

Before bringing these remarks on the Indus to a close, I wish to add a few words regarding the effect of the tide on the two rivers. In the Ganges it runs considerably above Calcutta, while no impression of it is perceptible in the Indus twenty-five miles below Tatta, or about seventy-five miles from the sea. We are either to attribute this occurrence to the greater column of water resisting the approach of the sea, “whose vanquished tide, recoiling from the shock, yields to the liquid weight;” or to the descent of the delta of the one river being greater than that of the other. The tide in the Indus certainly runs off with incredible velocity, which increases as we near the sea. It would appear that the greatest mean rise of tide in the Ganges is twelve feet: I found that of the Indus to be only nine feet at full moon; but I had, of course, no opportunity of determining the mean rise of the tide as in the Ganges. The tides of Western India are known to exceed those in the Bay of Bengal, as the construction of docks in Bombay testifies; and I should be disposed to consider the rise at the mouths of the Indus and Ganges to be much the same. Both rivers, from the direction they fall into the ocean, must be alike subject to an extraordinary rise of tide from gales and winds; and, with respect to the whole coast of Sinde, the south-west monsoon blows so violently, even in March, as to break the water at a depth of three or four fathoms from the land, and long before its depressed shore is visible to the navigator.