end of November, it gradually 1effens 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; becaufe few people have made experiments on the heights to which the periodical flood rifes in different places. The circumstance I allude to, is, the difference of the quantity of the increase (as expreffed in the foregoing table) in places more or lefs 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 circumstances 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 zi 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 precise 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 seafons; 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 furface of the river there, during the dry feason, is about 80 feet above the level of the fea at high water. Thus far does the ocean manifest 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 nearly 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 folution; which is, that the lowness 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 removed 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 anfwer to this, I fhall obferve, that it is proved by experiment, that at any given time, the quantity of the increase 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 80,000 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 alfo 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 opposite 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 interpretation 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 ascertain the precife length of its course. After winding with a rapid current 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 if 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,

alterin

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

Father Du Halde expreffes his doubts concerning the course 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 juftified by the information which his materials 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 refearches, 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 juftly efteemed 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 lefs furprifed, 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 course to within a hundred miles of the place where Du Halde left the Sanpoo. Icould 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 last 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 Du Halde leaves the Nou Kian, i 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 stream 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 junction 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 iflands, fome of which nval, in fize and fertility, our Ifle of Wight. The water at ordinary times is hardly brackish at the extremities of thefe iflands; and, in the rainy feafon, the fea (or at least the furface of it) is perfectly frefl 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 first 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 diftance 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 fhore, and make for fafety to the middle of the river.

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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 pafs at fpring tide. After the tide is fairly past the islands, no veftige of a Bore is feen, which may be owing to the great width of the Megna, in comparison with the passages between the islands; but the effects of it are vifible enough by the fudden rifing of the tides.

man skin. It was also very natural to imagine, that fince refpiration injures and phlogisticates air, the perfpiration of the body, fenfible and infenfible, fhould do the fame; and they who fuppofe that phlogiston converts common air into fixed air, must of course imagine, that the air contiguous to the skin is continually undergoing this change. Dr. Ingenhoufz afferts the former, and Mr. Cruikfhank, after Sig. Mofcati, the latter. On both these subjects I fhall make fome animadverfions, and likewise a few experiments that I think will be deemed conclufive, on the subject of perspiration, and fufficient to confirm what I have advanced with refpect to it in my last volume.

Dr. Ingenhoufz not only fupposes that air is continually iffuing from the human skin; but he took pains to collect it, in a confiderable variety of circumftances, of which he has given a particular account, p. 129. This I took the liberty to tell him I had do doubt was a deception; the air that he found not having come from the fkin, but from the water in which it was plunged: and both the quality of the air that he found, and the circumftances in which he procured it, left me no doubt upon the fubject. It was juft that mixture of fixed air, and partially phlogisticated air, that pump water, which he recommends for the purpose, generally abounds with. The bubbles of air rifing and fwelling at the fame part of the skin, is by no means any proof that the air came from the fkin: for that is always the cafe with air iffuing from water, the air bubbles never rifing within the water itself, but

always from fome other body immerfed in it. All the phænomena he has described may be feen with a piece of metal, or glafs, plunged in water containing air, in an exhaufted receiver; in which case it is cafily fhewn, that the air does not come from the pores of the metal, or of the glafs, but from the water itself; for if the water contain no air, and the furfaces of the metal and of the glass be carefully wiped, that appearance cannot be produced.

He fays that water exhausted of its air is not proper for this experiment, because it readily absorbs all the air as fast as it iffues from the skin. But if the experiment be made in water at all, this must be the only unexceptionable manner of making it; and water by no means absorbs any kind of air fo faft as he defcribes this to iffue from the fkin, and especially fuch a kind of air as he defcribes, a great proportion of which is air partially phlogifticated. It requires a long time before water, in a quiefcent ftate, will take up any fenfible quantity of fuch air as this. Befides, there is nothing that we know of the human frame, that would lead any perfon to fufpect that air ever iflues from the skin. Where are the air veffels for that purpose ? and what is their origin, or connection with other parts of the fyftem? The prefent ftate of anatomy indicates nothing on this fubject.

To fatisfy my friend, not myfelf, I told him I would make an experiment, which I did not doubt would convince him of his mistake in this refpect: I did it in the following manner : I boiled a quantity of rain water, in order