9th instant, and have now the pleasure to haud you the results, begging permission to make a few remarks upon the singularly interesting facts, which have been established by these and the preceding analysis.

The waters in every case were sealed with great care, and were perfectly preserved.

The first bottle which I opened was labelled, " Water from the river Bango,* taken at forty miles distance from the mouth, by her Majesty's schooner Fair Rosamond, on the 26th of December, 1839, in latitude 8° 33' south, and longitude 12° 41' east." The water emitted a very strong smell of sulphuretted hydrogen. It was tolerably clear, but contained a little gelatinous matter which resembled spawn of fish. The sediment of the whole bottle, however, when dried, only weighed fifteen hundredths of a grain.

The results of the analysis calculated for the imperial gallon, were as follows:

Specific gravity, 1026.4.

Sulphuretted hydrogen, 4-35. Cub. in.
Dry salts, 2736 grs.:

Consisting of Chlorine 1513, Sulphuric Acid 128, neutralized by bases, which have not yet been quantitatively determined, but consisting of Sodium, Magnesium, Calcinon, &c.

The second bottle was marked, "Water taken by her Majesty's schooner Fair Rosamond, off the Bango and Dande Rivers, latitude 8° 29' south, longitude 12° 33′ east, on the 29th of December, 1839." Results of analysis, Specific gravity 1026.7.

There was no odour of sulphuretted hydrogen in this water, neither was any detected by tests. The quantity of dry saline matter, per gallon, 2624 grains, consisting of Chlorine 1430, Sulphuric Acid 125.4, neutralized by the same bases.

It would have been better if the state of the tide had been noted, when the specimens were taken,-for you will observe, that the water forty miles up the Bango, contains quite as much saline matter as that taken from the mouths of the two rivers, and both as much as the water taken from Cape Lopez Bay. The state of the tide must, I imagine, greatly influence the ingredients of the water near the mouths of rivers.

It is impossible not to speculate upon the origin of the deleterious gas, which has now been proved to impregnate the waters upon the Western Coast of Africa, in such enormous quantities, through an extent of more than sixteen degrees of latitude. The supposition that it may have been generated by the spontaneous change of any of the contents of the water after it was sealed up in the bottles may be set aside by the slightest consideration.

It appears to me, that there are only two sources to which it can with any probability be referred, namely, submarine volcanic action, in which case its evolution might be considered direct or primary; and the reaction of vegetable matter upon the saline contents of the water, in which case it would be secondary.

The river Bango falls into the Bango bay to the north-east of St. Paul de Loando, and though the water analyzed was taken in one instance forty miles up the river, yet by Capt. Owen's chart, the positions given are more than thirty miles outside, (i.e. to seaward) of St. Paul de Loando.-ED.

The probability of a volcanic origin is, I think, small, from the absence, I believe, of any other indications of volcanic action, and from the great extent of the coast along which it has been traced.

What is known of the action of vegetable matter upon the sulphates, and the immense quantities of vegetable matters which must be brought by the rivers within the influence of the saline matters of the sea, renders on the contrary, the second origin extremely probable. Decaying vegetable matter abstracts the oxygen from sulphate of soda, and a sulphuret of sodium is formed. This again acting upon water, decomposes it, and sulphuretted hydrogen is one of the products of the decomposition. You will perceive that there is a large proportion of the sulphates in the different specimens of water which have been analyzed, and there can be little doubt, I imagine, that extensive mud banks must be formed at the mouths of most of the rivers on the western coast of Africa, within the tropics, consisting chiefly of vegetable detritus in the exact state which is most favorable to the action which I have described. This view rests upon experimental evidence, and upon considerations of great cogency, derived from the unhealthiness of certain well known situations in which decaying matters from tropical vegetation are brought into contact with sea water. I feel more than ever convinced, that the evolution of sulphuretted hydrogen is intimately connected with the unhealthiness of such stations.

When this matter was first brought under my consideration, I was surprised that the nauseous smell which must necessarily be evolved from water impregnated with this gas, at so high a temperature as that of the equinoctial regions, had not been noticed. I have in consequence turned to some of the accounts of the late travels in Africa, to seek for evidence upon the subject; and in the narrative of an expedition into the interior of Africa, by the river Niger, by Macgregor Laird and R. A. B. Oldfield, I found the following important observations.

"The principal predisposing causes of the awful mortality, were in my opinion the sudden change from the open sea to a narrow and winding river, the want of the sea breeze, and the prevalence of the deadly miasma, to which we were nightly exposed from the surrounding swamps. The horrid sickening stench of this miasma must be experienced to be conceived: no description of it can convey to the mind the wretched sensation, that is felt for some time before and after daybreak. In those accursed swamps, one is oppressed not only bodily but mentally with an indescribable feeling of heaviness, langour, nausea, and disgust, which requires a considerable effort to shake off."

Now, these observations were made in the very locality from which some of the first waters, which I examined were taken, and nothing more is wanting to identify the cause of the rapid decay of the ship's copper with that of the mortality of the climate.

It has been experimentally found, that so small a mixture as a fifteen hundreth part of sulphuretted hydrogen in the atmosphere, acts as a direct poison upon small animals, and the sensations of languor and nausea, described by Mr. Laird, are exactly those which have been experienced by persons who have been exposed to the deleterious influence in small quantities.

The peculiar unhealthiness of mangrove swamps in all parts of the

world, I have little doubt, arises from that tree requiring salt water for its growth, and its decaying foliage being thus brought into immediate contact with the sulphates. The hypothesis also agrees with the fact, (which I believe has been established,) that the unhealthiness of such situations does not extend to any considerable distance from the

sea.

I am afraid of trespassing too much upon your valuable time, but I cannot conclude this report without suggesting to you the expediency of directing the surgeons, or other officers of vessels frequenting these coasts, to test the waters for sulphuretted hydrogen at different distances from the coast, and at different periods of the tide, and to make regular reports upon the subject. The test of a little solution of sulphate of copper, (or blue vitriol,) would be sufficient, and could be applied without any difficulty. Much valuable and practical information might be thus acquired with little trouble, which if it did not lead to the means of correcting an atmosphere so infected, would at any rate indicate localities to be avoided entirely, or only at particular

seasons.

The commanders and other officers of expeditions for exploring the coasts of Africa, should be directed to bestow particular attention upɔn the subject, and at all events not to linger in situations where the water affords indications of the noxious gas.

I have the honor to remain, &c.

J. F. DANIELL.

An instance in which the same deleterious gas, namely sulphuretted hydrogen, was produced in a very serious degree from mercury, has also been pointed out to us by Sir John Barrow. In the year 1810, H.M.S. Triumph, commanded by Capt. Linzee, received on board thirty tons of quicksilver, in leathern bags, which from being wet, rotted and burst, and their contents became diffused through the ship, affecting to salivation about two hundred officers and men. The smell of the bilge water was so offensive, that even the carpenter's mate had much difficulty in sounding the well, being attacked with giddiuess to an alarming extent. The ship was cleaned well out, and sweetened; but it became necessary to send many hands to the hospital at Plymouth, and Dr. Baird was called on to report on the subject. After giving his own opinion in writing, he forwarded to the Secretary of the Admiralty the following statement of Dr. Pearson, teacher of Chemistry on the cause of the noxious gas.

"From well established principles, as well as analogies a reasonable explanation may be given of the effects attributed to thirty tons of quicksilver exposed on board the Triumph in bilge water, with rotten leather in bags, in a hot climate, in the beginning of summer.

"The stinking gas which was generated, was sulphuretted, and, perhaps, phosphorated hydrogen gas, mixed with carbonic acid, and, perhaps other gases; compounded by the putrefaction of animal and vegetable matter, the deadly suffocating effects of which are fully ascertained, unless mixed with a large proportion of fresh air; and the tarnishing of

OBSERVATIONS ON THE SHINGLE OF THE ENGLISH CHANNEL.

29

metals at a great distance even mixed with fresh air in a large proportion, is a well-known effect of sulphuretted hydrogen.

"It will be understood that the sulphur and phosphorus are furnished, probably, by the decomposition of sulphuric and phosphoric acids, always present in all kinds of animal matter. The hydrogen gis is furnished by the decomposition (chiefly) of the water. The carbon c acid is compounded by the union of the charcoal of the animal and vegetable matter, with the oxygen principally of the water.

"The stink is now imputed to the mixture of sulphuretted and phosphoretted gases, with putrefying matter. If the leather bags of quicksilver had been kept dry, they would not have putrefied, but probably would have retained the metal, and the above effects would not have happened."

To Dr. Baird.

G. PEARSON,
George Street, Hanover Square,
August 9th, 1810.

OBSERVATIONS ON THE SHINGLE of the BRITISH CHANNEL AS AFFECTING

BAR HARBOUrs,

SIR.—I am induced to offer a few remarks relative to the shingle of the English channel, because (like Lieut. Evans,) it has often engaged my attention; and because it is a subject replete with interest, and its investigation by men of different opinions, must assist in developing facts of infinite importance to civil engineering, in the construction of New Harbours of Refuge, or the improvement of such as are rapidly going to decay.

I should most willingly concede to Lieut. Evans the possibility of removing the shingle from the entrances of bar harbours, if in such an operation we were moving in the same course with dame Nature, for while the old lady invites us continually, by following her, to assist and benefit ourselves, she most resolutely opposes any attempt on our part to stay her progress; and thus it is our easiest method to advance where she retires, and to seize every vantage ground she leaves open to us. Reasoning thus, I believe, that where she presents us with a bank of shingle, or a mound of earth, it would be less laborious, and consequently less expensive to secure it by the addition of artificial means, than to carry it away to another site, more especially in situations where her efforts would be incessant, and her supplies comparatively inexhaustible. Let us, as respects the shingle, take Dover as an example, that being a position of undeniable consequence as a port contiguous to France, and being of all others most seriously inconvenienced by this said shingle.

Now, I am of opinion, that if half the sums expended in fruitless attempts to sluice and blow it out, and carry it away into deep water, in order to preserve the entrance to Dover harbour, (I repeat,) if half those sums had been appropriated to the erection of a jetty and groin to the south-westward of the piers, and if these extensions outward into deep water had been conducted by a skilful engineer, in accordance

with known natural causes and effect, that Dover might now possess one of the best artificial harbours in Europe, and protected by fortifications in every way suited to its importance. I am aware that the owners of property on the marine parade, (which encircles the bay,) will exclaim against this, because the very shingle bank which ruins the port, is a bulwark of safety to them, but the bank and beach they at present possess might also be secured to them by groins and jetties,* But what would these good conservators of the Cinque Ports say to Lieutenant Evans plan, (if practicable,) for taking up these millions of tons of shingle, and moving it into the interior for the manufacture of glass and pottery, or the repairing of the roads! Why the whole town of Dover stands upon shingle strata! The sea, in ancient times flowed up into a haven, and as it beneficently deposited its shingle along the base of the cliffs, the natives located themselves upon its surface. The hovel of the smuggler and fisherman first consolidated the soil upon which the opulent and flourishing town of Dover now stands. I have before me a plan of Dover harbour, as by survey, made in the reign of Elizabeth, and its evidence is conclusive, that as the beaches were thrown up and increased, there remained but one alternative to manual labour in the continuance and formation of its harbour, and the piers were from time to time advanced. In this process, harbours become the nucleus of valuable localities, a national gain, because wrested from the sea, and surely it is EASIER to secure and consolidate a bank of shingle, than to take it up and transport it by land to any distance, however inconsiderable. It is fighting with natural causes, in lieu of turning them to account and directing their effects. I am not alone in my opinion, that the piers at Dover should be again ADVANCED and carried out into deeper water.+

Lieutenant Evans recommends the employment of convicts, in the removal of the shingle to a distance from the port, but labour of that kind, (or slave labour,) to be available, must be stationary; a single sentinel can guard a gang of pile drivers with more security and ease than a detachment of rank and file would a gang of the same description traversing to a distance, with the necessary vehicles of transport.

The pent at Dover, which takes its name from water pent in, or shut up, as in all wet docks or reservoirs, has been formed by the bank of shingle thus deposited along the line of the bay. This bank turned the little river Idle from its natural course, along the base of the cliffs, till issued where the mouth of the present harbour exists. When Mr. Pitt was Lord Warden, it was in contemplation to cut through this bank, restore the backwater to its natural course, and run out two parallel piers into the deep water of the bay. The sacrifice of property would have been great, and the expense enormous; and so tenacious were the authorities of the preservation of this bank, that the inner side of it was not allowed to be excavated, for the formation of docks or slipways. Mr. Divine, in or about the year 1802, had commenced a building slip, but on his disturbing the inner surface of this bank, the backwater which had been shut in for scouring the harbour entrance, was sensibly diminished by drainage, as it escaped through the shingle into the bay. His work was stopped, and the site of his timber yard, and the old rope walk, are now covered by splendid mansions.

Lieut. Worthington's plan, and others, contemplate the extension of the southwest pier. If an open jetty of timber succeeded, it would be well; and if not, it would be easy to form dickey works on its exposed side, with this very shingle bar, on the principle of the Dutch embankments, or the Dimchurch wall.