I am aware of an objection that may be made to the above folution; 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 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 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 80,000 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 discharged in a fecond at that feafon is 405,000 cubic feet. If we take the medie

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

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 interpretation as the Gonga of Hindooftan : namely, the River. The courfe 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 course. After winding with a rapid current through Thibet, it washes the border of the territory of Lassa (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 westernmoft 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 Aflam. After its entry into 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 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 juftified by the information which his materials afforded him: for the Burrampooter was reprefented to him, as one of the inferior ftreams 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 eaft; although all the former accounts reprefented it as from the north; and this unex

pected 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 Du Halde leaves the Nou Kian, in its course 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 laft 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 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 islands, fome of which rival, 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 fresh to the diftance of many leagues out.

The Bore (which is known to be a fudden and abrupt influx of the tide into a river or narrow trait) 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 fmaller; 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 distance it near 70 miles. At Calcutta, it fometimes 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 past the islands, no vestige of a Bore is feen, which may be owing to the great width of the Megna, in comparison with the paffages between the islands; but the effects of it are visible enough by the fudden rifing of the tides.

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

HAVE fometimes found it ne

ceffary, though it is by no means agreeable to me, to correct the mistakes of others on the fubject of which I am treating; and I must appropriate this section 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 fhould be thought to iffue from the hu

man

man skin. It was alfo 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, muft of courfe imagine, that the air contiguous to the skin is continually undergo ing this change. Dr. Ingenhoufz afferts the former, and Mr. Cruikfhank, after Sig. Mofcati, the latter. On both thefe fubjects I fhall make fome animadverfions, and likewife a few experiments that I think will be deemed conclufive, on the subject of perfpiration, 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 fkin; but he took pains to collect it, in a confiderable variety of circumstances, 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 circumstances 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 kin: 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 defcribed may be feen with a piece of metal, or glafs, plunged in water containing air, in an exhaufted receiver; in which cafe it is eafily fhewn, that the air does not come from the pores of the metal, or of the glass, 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 faft as it iffues from the fkin. 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 abforbs any kind of air fo faft as he defcribes this to iffue from the fkin, and especially fuch a kind of air as he describes, a great proportion of which is air partially phlogisticated. 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 person to fufpect that air ever iffues from the fkin. Where are the air vessels for that purpofe? 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

to expel from it all the air it might contain, and then fat with my naked arm plunged in a veffel filled with it, after carefully wiping off, under water, all the bubbles of air that adhered to it. But though I continued to fit in this manner a full half hour, not a fingle bubble of air made its appearance afterwards. I might have examined whether this water had contained any air, befides what it might have been fuppofed to have imbibed from the atmofphere in this interval; but I neglected to do it, and am very confident it was quite unneceffary.

After this I need not fay any thing to my friend's ingenious obfervations on the air which he took the pains to collect from the skins of old and young perfons, and his laudable endeavours to remove a popular prejudice concerning the unwholesomeness of the former, and the wholesomeness of the latter kind of air.

Mr. Cruikshank's experiments, if they could be depended upon, would both prove that fixed air is compofed of common air and phlogifton, and that the perfpiration of animal bodies, in a healthy ftate, has the fame effect upon air that breathing it has, viz. phlogifticating it, and making it noxious, which is contrary to the experiments of which I gave an account in my laft publication; by which it appears that the air under my arm-pits, and near other parts of my body, was never lefs pure than the external air. The Abbé Fontano alfo told me, that he had always found the fame refult in experiments made upon himfelf. But Mr. Cruikshank fays (in the fecond edition of his Letter to Mr.

Clare, printed in Mt. Clare's Treatife on Abfceffes) that, after he had confined his leg in a glafs veffel, fo as to prevent all communication with the external air, lime water poured into it immediately afterwards, came out a little turbid. But this he would probably have found to be the cafe with a fmall quantity of lime water poured into and out of any veffel of the fame fize, on account of the great furface of the fluid that muft, in those circumftances, have been exposed to the common atmosphere; in confequence of which it is always known to attract fixed air!

However, partly to examine this matter more thoroughly, and with a variation that I had thought of, I repeated the experiments on my own perfpiration in various ways, and they all confirmed what I advanced before, viz. that the perfpirable matter has no fuch.. effect upon the air, but leaves it as wholesome, that is, as fit for refpiration. as ever, judging by the test of nitrous air, which, however, Mr. Cruikshank does not fay that he ever applied in this cafe.

Purfuing his fteps, I faftened a moift ox's bladder, containing about a quart of air, close about my ancle, fo that my foot, clean wafhed and warm, as his was, was expofed to it; and I fat near the fire, fo as to keep my foot properly warm a full hour. After this I carefully withdrew my foot from the bladder, without changing the air; and applying the teft of nitrous air, the air in the bladder appeared to be of the fame degree of purity with the external air; the meafures of the teft, ap