main too long inundated, were they not guarded by dikes or dams, from fo copious an inundation as would otherwife happen from the great elevation of the furface of the river above them. Thefe dikes are kept up at an enormous expence; and yet do not always fucceed, for want of tenacity in the foil of which they are compofed.

During the fwoln ftate of the river, the tide totally lofes its effect of counteracting the ftream; and in a great measure that of ebbing and flowing, except very near the fea. It is not uncommon for a ftrong wind, that blows up the river for any continuance, to fwell the waters two feet above the ordinary level at that feafon : and fuch accidents have occafioned the lofs of whole crops of rice. A very tragical event happened at Luckipour in 1763, by a strong gale of wind confpiring with a high fpring tide, at a feafon when the periodical flood was within a foot and a half of its higheft pitch. It is faid that the waters rofe fix feet above the ordinary level. Certain it is, that the inhabitants of a confiderable diftrict, with their houfes and cattle, were totally fwept away; and, to aggravate their diftrefs, it happened in a part of the country which fcarce produces a fingle tree for a drowning man to escape to.

Embarkations of every kind traverfe the inundation: thofe bound upwards, availing themfelves of a direct course and still water, at a feafon when every itream rushes like a torrent. The wind too, which at this feafon blows regularly from the foutheaft, favours their progrefs; info

.

Ft. In. Ft. In,

60 2 4

96

In May it rofe
June
July
Inthe 1ft half of Aug. 4 o

12 6

32 0

Thefe obfervations were made in a feafon, when the waters rofe rather higher than ufual; fo that we may take 31 feet for the medium of the increase.

The inundation is nearly at a fland for fome days preceding the middle of Auguft, when it begins to run off; for although great quantities of rain fall in the flat countries, during Auguft and September, yet, by a partial ceffation of the rains in the mountains, there happens a deficiency in the fupplies neceffary to keep up the inundation. The quantity of the daily decrease of the river is nearly in the following proportion: during the latter half of Auguft, and all September, from three to four inches; from September to the

end

end of November, it gradually leffens from three inches, to an inch and a half; and from November to the latter end of April, it is only half an inch per day at a medium. These proportions muft be understood to relate to fuch parts of the river as are removed from the influence of the tides; of which more will be faid by and by. The decrease of the inundation does not always keep pace with that of the river, by reafon of the height of the banks; but after the beginning of October, when the rain has nearly ceafed, the remainder of the inundation goes off quickly by evaporation, leaving the lands highly manured, and in a state fit to receive the feed, after the fimple operation of plowing.

There is a circumftance attending the increase of the Ganges, and which, I believe, is little known or attended to; because few people have made experiments on the heights to which the periodi cal flood rifes in different places. The circumstance I allude to, is, the difference of the quantity of the increafe (as expreffed in the foregoing table) in places more or less remote from the fea. It is a fact, confirmed by repeated experiments, that from about the place where the tide commences, to the fea, the height of the periodical increase diminishes gradually, until it totally disappears at the point of confluence. Indeed, this is perfectly conformable to the known laws of fluids: the ocean preferves the fame level at all feafons (under fimilar circumftances of tide), and neceffarily influences the level of all the waters that communicate with it, unless precipitated in the VOL. XXIV.

form of a cataract. Could we fup pofe, for a moment, that the increafed column of water, of 31 feet perpendicular, was continued all the way to the fea, by fome preternatural agency whenever that agency was removed, the head of the column would diffuse itself over the ocean, and the remaining parts would follow, from as far back as the influence of the ocean extended; forming a flope, whofe perpendicular height would be, 31 feet. This is the precife ftate in which we find it. At the point of junction with the fea, the height is the fame in both seasons at equal times of the tide. At Luckipour there is a difference of about fix feet between the heights in the different feafons; at Dacca, and places adjacent, 14; and near Cuftee, 31 feet. Here then is a regular flope; for the distances between the places bear a proportion to the refpective heights. This flope must add to the rapidity of the ftream; for, fuppofing the defcent to have been originally four inches per mile, this will increase it to about five and a half. Cuftee is about 240 miles from the fea, by the courfe of the river; and the surface of the river there, during the dry feafon, is about 80 feet above the level of the fea at high water. Thus far does the ocean manifeft its dominion in both seasons in the one by the ebbing and flowing of its tides; and in the other by depreffing the periodical flood, till · the furface of it coincides as near ly with its own, as the descent of the channel of the river will admit.

Similarcircumftances take place in the Jellinghy, Hoogly, and

E

Burram

I am aware of an objection that may be made to the above folu-, tion; which is, that the lownefs of the banks in places near the fea, is the true reafon why the floods do not attain fo confiderable a height, as in places farther re moved from it, and where the banks are high; for that the river, wanting a bank to confine it, diffufes itself over the furface of the country. In answer to this, I fhall obferve, that it is proved by experiment, that at any given time, the quantity of the increafe in different places, bears a juft proportion to the fum total of the increase in each place refpectively: or, in other words, that when the river has rifen three feet at Dacca, where the whole rifing is about 14 feet; it will have rifen upwards of fix feet and a half at Cuftee, where it rifes 31 feet in all.

The quantity of water difcharged by the Ganges, in one fecond of time, during the dry feafon, is 80,oco cubic feet; but in the place where the experiment was made, the river, when full, has thrice the volume of water in it; and its motion is also accelerated in the proportion of 5 to 3: fo that the quantity difcharged in a fecond at that feafon is 405,000 cubic feet. If we take the medi

um the whole year through, it will be nearly 180,000 cubic feet in a fecond.

THE Burrampooter, which has its fource from the oppofite fide of the fame mountains that give rife to the Ganges, first takes it courfe eastward (or directly oppofite to that of the Ganges) through the country of Thibet, where it is named Sanpoo or Zanciu, which bears the fame interpreta tion as the Gonga of Hindooftan : namely, the River. The course of it through Thibet, as given by Father Du Halde, and formed into a map by M. D'Anville, though fufficiently exact for the purposes of general geography, is not particular enough to afcertain the precife length of its courfe. After winding with a rapid cur rent through Thibet, it washes the border of the territory of Laffa (in which is the refidence of the grand Lama), and then deviating from an eaft to a fouth-east course, it approaches within 220 miles of Yunan, the westernmost province of China. Here it appears, as it undetermined whether to attempt a paffage to the fea by the Gulf of Siam, or by that of Bengal ; but feemingly determining on the latter, it turns fuddenly to the weft through Affam, and enters Bengal on the north-eaft. I have not been able to learn the exact place where it changes its name; but as the people of Affam call it Burrampoot, it would appear, that it takes this name on its entering Affam. After its entry in to Bengal, it makes a circuit round the western point of the Garrow Mountains; and then,

altering

altering its courfe to fouth, it meets the Ganges about 40 miles from the fea."

Father Du Halde expreffes his doubts concerning the courfe that the Sanpoo takes after leaving Thibet, and only fuppofes generally that it falls into the gulf of Bengal. M. D'Anville, his geographer, with great reafon fuppofed the Sanpoo and Ava River to be the fame: and in this he was justified by the information which his inaterials afforded him: for the Burrampooter was reprefented to him, as one of the inferior streams that contributed its waters to the Ganges, and not as its equal or fuperior; and this was fufficient to direct his researches, after the mouth of the Sanpoo River, to fome other quarter. The Ava River, as well from its bulk, as the bent of its courfe for fome hundred miles above its mouth, appeared to him to be a continuation of the river in queftion and it was accordingly defcribed as fuch in his maps, the authority of which was justly esteemed as decifive; and, till the year 1765, the Burrampooter, as a capital river, was unknown in Europe..

On tracing this river in 1765, I was no less surprised, at finding it rather larger than the Ganges, than at its courfe previous to its entering Bengal. This I found to be from the east; although all the former accounts reprefented it as from the north: and this unexpected discovery foon led to enquiries, which furnished me with an account of its general courfe to within a hundred miles of the place where Du Halde left the Sanpoo. I could no longer doubt,

that the Burrampooter and Sanpoo were one and the fame river: and to this was added the pofitive affurances of the Affamers, "That their river came from the Northweft, through the Bootan mountains." And to place it beyond a doubt, that the Sanpoo River is not the fame with the river of Ava, but that this laft is the great Nou Kian of Yunan; I have in my poffeffion a manufcript draught of the Ava River, to within 150 miles of the place where Ďu Halde leaves the Nou Kian, in its courfe towards Ava; together with very authentic information that this river (named Irabattey by the people of Ava) is navigable from the city of Ava into the province of Yunan in China.

The Burrampooter, during a courfe of 400 miles through Bengal, bears fo intimate a refemblance to the Ganges, except in one particular, that one defcription may ferve for both. The exception I mean, is, that during the last 60 miles before its junction with the Ganges, it forms a ftream which is regularly from four to five miles wide, and but for its freshness might pass for an arm of the fea. Common defcription fails in an attempt to convey an adequate idea of the grandeur of this mgnificent object; for,

I have already endeavoured to account for the fingular breadth of the Megna, by fuppofing that the Ganges once joined it where the Iffamutty now does; and that their joint waters fcooped out its prefent bed. The prefent junc tion of these two mighty rivers below Luckipour, produces a body of running fresh water, hardly to be equalled in the old hemifphere, and, perhaps, not exceeded in the new It now forms a gulf interfperfed with islands, fome of which rival, in fize and fertility, our Jile of Wight. The water at ordinary times is hardly brackish at the extremities of these islands; and, in the rainy feafon, the fea for at least the furface of it) is perfectly fresh to the distance of many leagues out.

The Bore (which is known to be a fudden and abrupt influx of the tide into a river or narrow ftrait) prevails in the principal branches of the Ganges, and in the Megna; but the Hoogly River, and the paffages between the iflands and fands fituated in the gulf, formed by the confluence of the Ganges and Megna, are more fubject to it than the other rivers. This may be owing partly, to their having greater embouchures, in proportion to their channels, than the others have, by which means a larger proportion of tide is forced through a paffage comparatively smaller; and partly, to there being no capital openings near them, to draw of any confiderable portion of the accumulating tide. In the Hoogly or Calcutta River, the Bore commences at Hoogly point (the place where the river firft contracts itself), and is perceptible above Hoogly

Town; and fo quick is its motion, that it hardly employs four hours in travelling from one to the other, although the distance it near 70 miles. At Calcutta, it sometimes occafions an inftantaneous rife of five feet and both here, and in every other part of its track, the boats, on its approach, immediately quit the hore, and make for fafety to the middle of the river.

In the channels, between the islands in the mouth of the Megna, &c. the height of the Bore is faid to exceed twelve feet; and is fo terrific in its appearance, and dangerous in its confequences, that no boat will venture to pass at fpring tide. After the tide is fairly paft the iflands, no veftige of a Bare is feen, which may be owing to the great width of the Megna, in comparison with the paflages between the islands; but the effects of it are visible enough by the fudden rifing of the tides.

Of the Air that has been supposed to come through the Pores of the Skin, and of the Effects of the Perfpira tion of the Body; from Priestley's Experiments in Natural Philofophy.

HAVE fometimes found it ne

ceffary, though it is by n means agreeable to me, to correct the mistakes of others on the subject of which I am treating; and I must appropriate this fection to that business.

It cannot be thought extraordinary, that when it has been imagined that air is extracted from the moft compact bodies, as gold, by means of the air pump, it should be thought to iffue from the hu

man