6. Barking shelf commences opposite the creek, continuing nearly half a mile down, and extends across nearly two-thirds of the river, with from 6 to 10 feet only in the line of navigation. This is considered the worst shoal in the river. The Trinity lighters have for many years worked at the place, and have taken up an immense quantity of gravel; but the greater part of the clay and peaty surface, which is the worst part of it, remains.

7. A shoal opposite Gallion's point extends from the north side about one-third across the river, with 7 feet.

8. Ham shelf, opposite Woolwich dockyard, extends from the north sbore upwards of half way across the river, for a length of a quarter of a mile, exclusive of patches and projections higher up, and has upon a great part of it only 6 feet.

9. Bugsby hole is altogether a shoal water reach, in places only 8 to 9 feet; with some shelves and small shoals, having only 6 to 7 feet. 10. Immediately opposite the river Lea, a shoal extends from the north side to the middle of the river, with only 8 feet.

11. A little above the entrance of the Lea is a dangerous small rock of concreted gravel in the middle of the river, with only 9 feet.

12. Two "middle grounds" in the centre of the river, between Blackwall and Greenwich, have upon them 9 to 10 feet.

13. Whiting shoals, a little above the Commercial dock entrance, a dangerous shoal, in nearly the middle of the river, has in places only 7 feet.

14. Limekiln-shore dock, from the north side, goes nearly two-thirds across the river, with only a depth of 5 feet.*

From the last-named shoal up to London Bridge there are no other bad shoals.

I find, by calculation, that about 60,000l. would remove all these shoals from the line of navigation, and make a passage 12 feet deep at low water, were none of the materials suitable for ballast. The sum does not appear large, compared with the almost national object. The Birmingham Canal Company, for whom I am professionally concerned, are laying out nearly four times the amount in a new canal, 8 miles in length, fitted for the trade of narrow canal boats only, and intended, not for a new trade, or a new source of revenue, but to shorten the route for the present trade. chiefly of coals and iron, from the mines to Birmingham. A very small rate, say one eighth of a penny per ton, upon the trade, would effect it. The amount of tonnage which paid light dues on passing the Nore inwards in 1840, was 4,406,000 tons. My estimate for the still further improvement of the Clyde, for which an Act was passed in 1840, was 800,000l. Ought then the immense trade of the Thames to remain any longer impeded, and the vessels navigating it to continue any longer liable to delay and damage, if the cause of such impediment, delay, and damage can be removed for anything like the sum I have named?

Above London Bridge the character of the river is entirely different,

• The depths below bridge are taken from the excellent survey of Capt. Bullock, R.N., under the direction of the Admiralty. Those above bridge are by Mr. Comrie and Mr. May, under my direction.

owing, as has been before stated, to the piers of London Bridge, which existed for about seven centuries. Since their removal, some of the Trinity-House lighters have been employed at the request of the Lord Mayor and Port of London Committee, though above their legitimate range of action, and have taken upwards of 150,000 tons in the short space between London and Southwark bridges, which has cleared away the shoals there; but above Southwark Bridge they are so general, and so irregular in their position and depth, that it is difficult to describe them, except by reference to the plans and sections. The evil is increased by the gravel which is laid over the mooring stones, and raised improperly and unnecessarily above the general surface of the river's bed. It will be seen that many places in the middle of the river are above the level of low water, preventing all navigation for barges between half ebb and half flood, and making the passage for steam-boats tortuous and difficult between three-quarters ebb and the first quarter of flood, and such that when there is little land water in the river the smallest steam-boat cannot move at low water. The evidence already referred to, which was given on this subject in the session of 1840 by the masters of steam-boats, confirms this statement, if indeed that which may be so frequently witnessed by every passenger can require confirmation.

There are at present several wrecked vessels sunk in the navigable channel of the river. I do not pretend to know the law in such matters; but surely it is the duty of the owners of the vessels to raise, without delay, and remove such dangerous interruptions out of the highway of the river, especially as delay increases the difficulty of raising, and lessens the value of the wreck.

I have appended to this Report a Table, showing at various points the present and proposed width of the river, with the contraction on each side. It is not necessary for the public objects I have stated that every part should be embanked. To some it may be inconvenient in various ways; but if the unembanked part, or the dock, become private property, to be used only by the owner of the premises behind it, its value to him may thus be increased, and he might have the option of wharfing in the line of the adjoining quays, whenever he might wish to do so.

The effect of every erection between high and low water is to decrease the quantity of tidal or back-water, upon which the depth below these embankments mainly depends; and the embankments we are recommending for narrowing the river are of this character; but as the material for filling behind the embankments is to be taken from the bottom of the river, the effect of this will be to let the water ebb out lower, and thus to increase the space for the return of the flood and the back-water. I find, by calculation, that the lowering of the surface of the water above bridge one foot vertically for four miles in length will equal in cubic quantity the whole solid of the embankments above London Bridge.

In the time of heavy rains, the low lands up the river are liable to be flooded. Mr. Telford states that the height of low water at Teddington, during the land flood of December, 1821, was 7 feet above the high water of Trinity standard. The effect of the narrowing by

embankments will be to increase to a small extent, the obstruction to the descending floods at the first of the ebb; but this will be much more than compensated for by the additional depth which operates through the whole period of the ebb; so that the general measure will, as respects the drainage of the country, be a decided advantage.

Whatever wharfing is done in the proposed line should be done securely; and in case of failure a ready means of rebuilding, or at least of preventing a nuisance, is essential, whether it be a clay bank or a wharf wall. The public ought to be protected against damage by the owners of property abutting upon the river; and, if the owner neglect to do this, there is I apprehend, or surely ought to be, a power to compel him, as well as a summary way of abating the evil. This should extend to all unlawful or unauthorized erections within the line of high water.

I am afraid that in some points referred to in this Report I may have gone too much into detail-may have been in others too general-and may have entirely omitted matters of greater moment than those I have remarked on; but surely enough has been thought of and said to show the great, the almost national importance of the subject, and the capability of adding essentially, at comparatively little expense or trouble, to the commercial and general utility, and to the ornament of this noble river, for the navigation of which so little has been done during many centuries, and to the making of it still more instrumental to the comfort and health of the inhabitants, as well as contributing to the extent, beauty, and value of the property upon its banks.

I am, Sir,

Your most obedient servant,

23, Great George Street, 13th Dec., 1841.

JAMES WALKER.

CURRENTS OF the Ocean.-Extract from a letter addressed to the President of the Royal Geographical Society, by the Chevalier Harnett, dated Chateau de Stangbihan, Concarneau, June 16th, 1842.

"Sir.-The enclosed paper was yesterday found by a fisherman, contained in a bottle in the Bay of La Forêt, situate on the coast of Britany, close to the sea-port town of Concarneau, who, not being able to read it, brought it to me.

"In compliance with the request contained in it, I should have at once addressed it to Mr. Purdy, but from the great lapse of time since the bottle was thrown overboard, it is a question whether Mr. Purdy is still in existence, and if not, my letter would consequently be lost. Sir, "LE CHEVALIER HARNETT."

" I am,

yours, &c.

ENCLOSURE." His Majesty's frigate Blonde, 28th September, 1826, from Bermuda to [England?] Lat. by sun mer. alt. 43° 30' N., long. by four chronometers, 38° 30′ W.

"This bottle was thrown over by Mr. W. H. Hall, master of the Blonde, to ascertain the current. Whoever finds it will communicate the particulars by letter to John Purdy, Esq., Hydrographer, London, which will oblige Mr. H. and many others."

Remarks. If I may venture a conjecture upon this subject, from the knowledge of currents already acquired, I should say that the apparent course of the bottle was more or less to the northward and southward of east, until it was carried by the south-easterly inset into the Bay of Biscay, whence it was operated upon, both by tide and current, setting it to the north and north-west until it reached the snug little nook of La Forêt, to the northward of the Glenan Isles, where it lay in a state of repose until found as above described, in 1842.

A bottle from the " Bolivar," on the passage from the Cape of Good Hope, in lat. 46° 53′ N., long. 18° 46′ W., August 29th, 1840, was picked up near the coast of Barre de Mont, (Vendee), early in December, of the same year, 1840.

To the Editor, &c.

I am, Sir, yours respectfully,

JOHN PURDY.

June 19th, 1842.

[We place the foregoing letter on record from that careful and assiduous hydrographer, Mr. Purdy, the worthy compiler of those valuable works well known to our seamen, under the names of the "Atlantic Memoir," the "Columbian Navigator," the "Mediterranean Directory," and others that we might name, in order to preserve it for future reference in a general collection of the bottle tracks, in course of preparation for this journal.—ED.]

VARIATIONS OF THE COMPASS.-At a time when the subject of Magnetism is exciting general attention, the following results of observations, made evidently by a very intelligent Commander, may be acceptable. They were communicated to me some time ago by your respected friend and correspondent, Lieut. Evans of Bedminster, and I am unwilling that they should be lost.

An old Captain of the port of Bristol, named Olive, was a celebrated seaman of his day, and fought some actions when in command of the St. Andrew privateer.

In the year 1757, in lat. 50° 24′ N. long. 8° 20′ W. he found the variation of the compass to be 16° 11′ W.

In 1769, in the Strait of Florida, lat. 27° 45' Var. 6° 30′ E.

May 28-Lat. 30 17 long. 76 20 Variation per amplitude 3° 45' E.

at sun rise 3o E. sun set 1° E.

sun rise 1° 38′ W.

1769

sun rise 1 10 W.

(North side of the Gulf Stream.) The water still indicating soundAt one P.M. perceived the colour of the water change to that of the deep ocean.”

ings.

J. P.

THE MEAN TIDE LEVEL.

[It is right to state that, this paper was written a year or two ago, when the subject was brought under the notice of the British Association.-ED.]

"THAT there is nothing new under the sun" is a proverb as old as the time of King Solomon. The announcement by a member of the community of some (so considered) discovery in the sciences, the arts, and among the phenomena of nature is, generally, followed by a prior claim to the merit in some other individual. Undoubtedly, Sir, among talented minds, whether in theory or practice, similar ideas, conclusions, inferences, and the detection of a particular mode of action in nature, may arise, and be apparent, without any one of these individuals possessing even a knowledge of the existence of the others, much less of their thoughts, inventions, or discoveries; so that, merit, in degree, may be conceded to any one of these, without prejudice to that which should belong to, or be claimed for another.

It is presumable that, the naval officer whose discovery has been noticed, never knew that any other person had preceded him in the detection of this law of nature: credit, therefore seems attached to both. The paper on the mean level of the sea in the June number of the Nautical is highly interesting as exhibiting the same phenomenon, on another part of the British coast: the writer, however, has left the matter just where it was before. No doubt of the correctness of the principle has been expressed; the brief notice of it in the Athenæum was noted as not affording to those readers who were only possessed of a superficial knowledge of the lunar theory, a clear idea of the process.

The notice was this, viz:-1. "A constant sea-level, ascertained to be at three hours before, and three hours after high water."-2. "One invariable mean height common to neap and spring tides, the half-tide mark." In addition, we now have-3. "A point in the vertex equidistant from high and low water of any one tide, is on a level, or coincides with the points half-way between high and low water of every other tide." The first impression arising from these brief descriptions is, that there can be no inequality in the rise of the tides in the locality of the discovery; because, if there were, the point half-way between high and low water, or, what is familiarly understood as the half-tide mark, could not be on the same level throughout a semilunation, when the tides undergo their various changes.

If the ordinary minded man had read only that a constant recurringsea-level was found, in the estuary of the Mersey, to take place every tide, at three hours before high-water, and three hours after highwater, he might have been satisfied that he understood the fact; but, when he is informed that, this constant sea-level is "the half tide mark" which his practical observations point out to him is inconstant every tide for a given time,* he becomes perplexed, and requires farther expla

Coincidence in rise will happen in springs and neaps, which of course shows a coequal half tide mark.

ENLARGED SERIES.-NO. 9.-VOL. FOR 1842.

4 K