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Magnetic Equator.

The line of the Magnetic Equator has been hitherto ascertained by tbe Dipping Needle, which being possessed by few ships, renders observations upon the line very limited. Although less accurate, I conceive a tolerably near approximation to its site may be obtained by means of a soft iron bolt placed upright in the ship, which becoming magnetized by tbe earth's induction, would consequently denote the particular magnetic hemisphere the ship was in, by approximating one of its poles to the ship's compass, which would of course require to be frequently repeated during the day, when the magnetic power of the bolts' poles was found to be nearly extinct, reversing the bolt each time of trial, and assisting the magnetism by smart blows upon it with a hammer, while held in a perpendicular position. The medium point betw«en which the change of poles took place would of course denote the site of the Magnetic Equator.

Any iron belaying pin might, in case of necessity, be used as a test, a speedy change of poles in all the iron of a ship taking place, after passing from one magnetic hemisphere to another, particularly if som« of the cannon be fired in the interim. C.

West India Lighthouses.

Dear Sir.—I have now time to give you my ideas on the importance of a lighthouse on the east end of Barbados. This necessity was first agitated many years ago, but in 1835, Sir Charles Smith of the Engineers, and Sir George Cockburn, commanding on the West India station, agreed upon the spot on which to erect it.

The situation was well chosen, to embraee all the important objects in view; first as a land fall from Europe to a large portion of the West trade, including Columbia, and Venezuela; secondly for a very considerable trade from our North American possessions, and the United States, all of which call at the weathermost island first, to try the market before running to leeward, or call "to the order" of their consignee; and thirdly, for the benefit of the trade from British Guiana, which, would probably all pass to windward of Barbados, if they could boldly run for a light to enable them to pass in the night time; for want of this they keep away, and at once run to leew-.rd past St. Thomas, which bringing them so far to the westward obliges them also to pass to the westward of Bermuda, where these heavy laden ships are. sure to encounter the worst weather; whereas, if they had passed to windward of Barbados, they could with ease have gone to the eastward of Bermuda; and it is a well known fact the heavy north-west winds from the coast of America, do not extend there in their fullest force, therefore a comparatively fine weather passage is secured. The currents too are very unaccountable, though generally setting dead on the Coblers rocks, from the eastward and from the southward; I have been set between forty and fifty to the northward in less than twenty-four hours. This will easily account for the loss since 1835 of sixteen

vessels whose names are known, other numerous pieces of wrecks of vessels names unknown, besides vessels that have grounded, and succeeded in getting off. Why then should Barbados the land-fall of the West Indies be left without that safeguard to navigation a good lighthouse? What is the expense? a mere nothing in comparison to its importance; the estimate given in by Sir Charles Smith for a good solid lighthouse on the plan of the Eddystone, to withstand hurricanes, is 5092/. 2s. 6rf., on a spot 117 feet above the level of the sea, and being 83 feet more in height. The annual expense of maintaining it is 23 W. a trifling duty on shipping passing by, and on vessels coming into the bay (Carlisle) would be willingly submitted to by the shipowners. At Bermuda the preparations for a lighthouse on Gibbs Hill, are in a state of forwardness, and it probably will be completed before the expiration of 1841, by that talented expounder of hurricanes, Col. Reid, the governor.

At Jamaica also a sum of money has been voted, to place a light oil Morant Point, which is also in rapid progress in England. Now, I conceive neither of these places require it half so much as Barbados.

I have said the "unaccountable currents," however I do account for them satisfactorily to my own mind. The amazing quantity of water discharged from those great rivers on the coast of Guiana finding its way into the ocean, meets an obstruction to its natural course on the surface by the trade winds, which constantly throwing fresh supplies of ocean water, succeed in forcing the river discharges under, to such a depth, as being no longer acted upon by the face of the winds, this water re-asserts its right of course, and continues on till obstructed again by the island of Barbados; then, it again rises to the surface, and separating into two bodies, occasions that northerly current setting round both the east and west ends, though by far the strongest round the east end and over the Cobler Rocks. The same effect is likewise produced at Tobago, during the heavy rains. I have been set nearly due north seventy miles in the twenty-four hours, being once in the run of it,for probably four or five miles further to the westward, the set of the rivers Orinoco, being rebutted by the island would go off at a rapid rate to the westward, and this I have actually witnessed in a calm with two vessels. In every thing regarding currents in the West Indies, I am quite convinced that the strength of the trade winds would afford a close approximation to the truth; also the dry and wet season to be considered, as well as the direction of the land that may form the opposing power to the course of river discharges.

I have wandered from the lights, and now will resume with my own plan of lighting all the islands in the West Indies. The great object to be obtained by this, is to facilitate steam navigation, now about to be carried into effect on a large scale, and this will be easily shown by explaining that the steam vessels touch at the different islands, at all hours of the night; when, whatever may be the weather, the vessels are obliged to come in close to the shore to receive their passengers, and much valuable property, having from two to three hours only to perform this service, as also (o land and take in the mails. In dark nights it is frequently with the utmost difficulty that they can find the landiug places, therefore, I propose, that a triangular form of light be placed on a post, in the best situation to shew the anchorage, and act as a guide to the landing places. This form will be least likely to be mistaken for accidental lights. It must be remembered, the purpose for which these lights are proposed is not to make land-falls, or warn from distant dangers, but simply as above, to point out the harbours and landing places. The post may vary in height according to the situation in which it is erected, and the lights may be placed so as to serve as leading marks" to approach by; that is, on certain bearings a wrong direction may be indicated, by darkening one light or opening out another. With Barbados, a light placed in Carlisle Bay is more particularly required, to enable vessels to anchor at night. It frequently happens in the strong trade winds, that vessels waiting for daylight, are drifted by the current to leeward, and are unable to work up again without standing to the northward, thereby losing two or three weeks. I enclose a rough sketch of the proposed plan, and the estimate on the other side.

Annual.
Two pints of cocoa-nutl
oil <ls. per gall, daily/
Tow and for cleaning
Painting
Casual expenses .

£23 5 0

£23 1 0

Add to the above expense a shed, for trimming lamps and for the man attending to sleep in, because in the day time he may have other occupations which will reduce his wages.

I omitted to say in some of the islands, I would have the lights coloured, as frequently vessels mistake one island for another, making them at night, carelessly enough, but it does happen.

I shall shortly see the agent for Jamaica, and will then say exactly the sum they have voted, and what the progress they are making with their lighthouse. I remain, &c,

W. J. Whisij, Commander, RN.

23, We&tck Street, 15M Nov. 1840.

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Lighthouse Kor Morant Point, Jamaica.

A Meeting of the Commissioners of this Lighthouse took place in Spanish Town, Oct. 28th, 1840.

The clerk of the Commissioners read an extract from the Report of Mr. Alexander Gordon, the civil engineer in London, whereby it appeared that an Iron Tower would be the cheapest that could be chosen, and would cost 820/. sterling. The cost of lantern, lamps, reflectors, and apparatus will be about 1,450/., and fixing the same in lighthouse 150/., making in all 2,420/. sterling. The Commissioners agreed to report to the House; and to request that the Commissioners of Correspondence do communicate with the Island Agent, and request his assistance in carrying the intentions of the Legislature into effect.

Blare's Bow For Men-of-war.

Thr pages of a work dedicated to every scientific subject touching on nautical pursuits, cannot be considered to digress, when adverting to the improvements taking place in so important a part of our naval defence, as naval architecture; more particularly in its application to ships-ofwar, by contributing to render the battery they carry, more effective under all circumstances, and without any increase of weight of metal, any addition to their crews, or any extra expense of material, labour, or time.

There has recently been brought under our notice, a plan of Mr. Blake's, the master-shipwright of Portsmouth Dock-yard, for giving increased effect to the fortified bows of ships-of-war of all classes. By an alteration in the bow above the water line, double the number of guns can be brought to bear parallel with the keel, right ahead, to what could hitherto have been practicable; and in addition to this (which is an important improvement,) some of the guns from one bow can be so trained as to fire across the stem to an object on the opposite bow, thus giving to a chasing ship the means of crippling the ship she is pursuing, which was never before possessed, and enabling a ship attacked during a calm by steam vessels right ahead, to get a powerful battery to bear on the steamer, and thus rendering the bow, which has always been considered the weakest part of a ship-of-war for attack or defence, comparatively strong.

The advantages of this plan are likely shortly to be tested by practice, as the only ship ever constructed with Ihis improved bow, is the Vindictive, a 50-gun frigate now in dock at Portsmouth, preparing for commission. We cannot anticipate anything but ultimate success upon trial; and shall, therefore, hail with great satisfaction, after its having undergone the test successfully, its general adoption in ships of-war of all classes.

Any thing adding to our maritime strength, backed by the approbation of old and experienced naval officers, must be considered an acquisition by the whole of the community, but to professional men peculiarly so, and all will be ready to contribute their meed of praise to the originator of a plan so perfectly novel.

Lang's Tube Scuttles.

During the long war, commencing in the year 1703, and ending in 1815, our sailors suffered much from want of light and air in all ships, more particularly in the smaller classes, on their lower decks, for where the crew were berthed in these, it was total darkness, unless lighted by candles; not only this, but it almost amounted to suffocation in hot climates from want of ventilation; and the same was the case on the orlop decks of line-of-battle ships, and even on their lower gun decks when the guns were housed, and the ports shut. Here the crew were much inconvenienced by the muzzles nf the guns being secured to the clamp above, thus obstructing the light from the old square scuttles

which were placed in the ports. With a view to afford the accommodation so much needed, and to remedy the evil various methods were tried from time to time, without producing the desired effect.

About eighteen years ago, Mr. Lang, then assistant-surveyor of the Nary, invented a tube scuttle of a conical form, perfectly water tight, to be drawn in, or put out from the inside of the vessel when required for air, and always under all circumstances in the worst weather affording liijbt. This was first fitted in a sloop-of-war on the West India station, as an experiment, and being found to answer the purpose, it was afterwards introduced in several ships and vessels of various descriptions, and in 1831, was placed in the Thunderer, of 84, guns, on her orlop deck, on the Vernon frigate's lower deck, Magicienne razee corvette, and other smaller vessels, by which such great benefit and comfort to the health of ships companies have been obtained, that, we undertand, an order has been given directing that all ships of the line shall have them fitted on their orlop decks similar to the Thunderer. This ship, in consequence, of having these scuttles, and a more complete arrangement of the orlop deck, than is usually fitted, was enabled, in addition to her crew, wilhont displacing a gun, to accommodate a regiment of soldiers, on the said orlop deck, and convey them to Gibraltar, when, on the contrary, the Revenge, 74 guns, was obliged to take out her lower deck guns, and leave them iii England to enable her to effect a similar conveyance of troops, her orlop deck being like those of line-of-battle ships, without ventilation or light, encumbered with store rooms, &c, thus reducing the ship in her armament to that of a frigate, until her return to England, for her lower deck guns. In fact, the advantage that will now be gained by the general adoption of this system of ventilating in the British ships-of-war is incalculable, and these tube scuttles being placed between the lower deck ports of line-of-battle ships, will give 'he necessary light, and air, overMhe seamen's mess tables, when the lower deck guns are housed, and the ports closed. Thus the refreshing breeze is iotroduced between decks, instead of the former humid atmosphere.

Tube scuttles of the same description having been fitted in steamers, and small sailing vessels' sides; and ventilators, also invented by Mr. Lan», in addition on their decks, a current of air is produced when the hatchways are battened down in bad weather, by which, not only the sailors, but the engineers, and stokers have likewise shared in the advantages of this most useful invention.

Magnetism And Electricity.

The following account of an effect produced on a magnetized piece of iron, during the hurricane of September, 1838, at Nassau, was given me by a friend a short time since and will be found interesting to the scientific world.

A bar of iron about six inches long, and one-eighth inch square, having been given polarity by the majnet, was suspended by a piece of thread from a peg driven into the side of a wooden partition, which lying nearly north and south, allowed the bar to swing freely in the mag

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