curious phenomena. It would appear that the regularity of the S.E. trade wind is confined between the 90th and 140th degrees west. From New Britain and the other islands situated to the south of the line, a westerly monsoon blows; extending as far to the eastward as the Society Islands; commencing in December or January, and continuing to April or May, then succeeded by the S.E. wind.

The lateral extent of this westerly monsoon is about 15 degrees of latitude, but variable, the limit sometimes spreading three or four degrees more southerly; and northerly of the line it varies one or two degrees. It is not improbable that, the chain of islands between New Guinea and Taheiti, has some influence in its prolongation eastward; but I do not think these groups of islands are direct agents in its production; the alternation, however, appears to me to give the coup de grace to the theory of the rotary velocity creating the tropic wind.

I shall not attempt to search out the cause, though the subject is inviting, of this westerly monsoon; it would require much sober thought, and a regular course of inductive reasoning from the string of facts widely spread and lengthened out, besides an intimate knowledge of the natural philosophy of the atmosphere &c., before a satisfactory deduction could be drawn; which I do not feel myself competent to; and a more hasty opinion would be of little value in the general estimation.

I have now brought my prattle to a close, and have only to add that however we may be perplexed in our attempts to link cause with effect, we can have no hesitation, no difficulty, in assuring ourselves that mutation or change is a governing principle in nature with her, action is inseparable from a healthy state: it does not clash with her fixed laws.

I cannot refrain from expressing a hope that voyagers to the south of the equator will note the character of the trade winds, particularly the N.E., in order to determine what effect the very severe winter of the north, as well as the low temperature of air may have on the tropic wind; as, if theories be right, we should expect that it must have been brisk throughout the winter and spring; and should cold weather continue general in the northern latitudes, that there will be little flagging of the wind there whilst it lasts.

I have only now to make one more remark; it will show how puzzling the action of the wind is, for that which I am about to notice, seems paradoxical enough, opposed, in fact, directly contrary to the calorific process of flowing air; it is that, as far as we can depend upon the thermometer, our own sensation, and the evidence of our eye sight, wind from the sea of higher temperature than the air over the land, in the season of winter, flows, into the latter: but though it does this, it does not necessarily negative the contrary fact which experiments have proved.

I state this curious circumstance, which any body may verify who will be at the pains to give his attention to the changes of weather in winter, to show how much we have yet to learn about the causes of

*In the Nautical Magazine.

wind. What explanation can be given that will prove satisfactory? It is a very difficult question, because we have no means of obtaining actual proofs.

We may conjecture, perhaps, very reasonably, that the column of air in motion, when it receives its initial velocity is of very low temperature; but, as it progresses gradually becomes elevated, and still urged by the original impulsion, at length arrives at the land lying in its course, over which the air is of a much lower temperature, and so imparts its warmth, and hence thaw succeeds frost. If this be considered likely, it will show that the pressure at the fountain-head neutralizes the distinction between hot and cold air, under particular circumstances; but there is reason for believing that a warm column of air in motion is often arrested by another column of a lower temperature, so as to produce a calm intermediately; or, if the colder column be in motion, a commotion, from the action of some mediate cause.

The elucidation of these curious, and apparently contradictiory phenomena, however, can only be undertaken by a profound scientific and philosophic mind, and from long continued and close observation of facts carefully registered.

ABERRATION OF THE COMPASS.

31st December, 1847. on board the Iron Barque, Richard Cobden.

Lat. 49° N. Long. 16° 30′ W.

SIR.-I am led to offer you the following remarks, on the aberration of a compass on board the "Richard Cobden", for insertion in your columns, if you think them worthy the space, This vessel has made three voyages to India, but it is only the last two, that these notes refer

to.

In May 1846 three positions in this ship were corrected for the Local Attraction, by Mr. Gray of Liverpool, by the ordinary method of swinging the vessel in dock, and placing antagonist magnets in certain positions round the above places. These places are respectively, the binnacle, about 4 feet before the stern-post, a swinging tell-tale compass, placed in the cabin skylight, about 8 feet distant from the above, and a foremost binnacle, placed on the main deck, about 7 feet abaft the mainmast. They all swing about 2 feet from the deck.

We left Liverpool on June 10th, 1846, for Bombay, at which time all the compasses agreed with each other; and all were correct also, by the bearings of different well known objects, taken whilst in the river. The first aberration I observed was off Pernambuco, on the 12th July. For having lost the north-east trades far to the northward, and got but a very scant south-east trade, I was unable to weather the South American coast, and tacked to the eastward when about 6 miles from Pernambuco.

After tacking, I found the ship's head by the binnacle compass E.b.N.,

and by the other two compasses, east. Also I found by the binnacle, she took 13 points to come round in, which I attributed to the wind shifting whilst in stays; but on coming to examine the other compasses, and finding the above difference, I knew it must be aberration. Having stood off 24 hours, I tacked again to the westward, and found she took the same number of points again to go round by the binnacle, but by the other compasses 12 points; and I also found there was a point difference between the compasses when her head was S.W., the binnacle giving S.W.W., so that with her head to the westward, she increased the westerly variation, and with her head to the eastward she decreased it: in each case proving the north point of the compass to be driven forward. In my private journal and log book I called it easterly or westerly aberration, as her head was either to the eastward or westward. For in this case, it had to be allowed for on the course steered the same as westerly variation, and in that, the same as easterly.

As I proceeded to the southward, I found the binnacle compass varied more and more from the other two, till in the highest southern latitude I attained, it reached its maximum. For in 39° S. and 22° E.; there was 4 points aberration easterly (her head being to the eastward); viz. the ship's head was E.b.N. by the binnacle compass, and S.E.b.E. by the others. Also having occasion to tack about here, ship's head being north on the starboard tack by all the compasses, and the wind E.N.E., I found after tacking, her head to be east by the binnacle, and S.E. by the other compasses, so that whilst with the ship's head to the northward the aberration affected the binnacle compass, so as apparently to shift the wind 4 points in our favour, whilst in stays; yet, when her head was to the southward it affected the compass the other way. Also when her head was either north or south, there was no aberration apparent, all the compasses agreeing together, but the aberration arose and gradually increased as her head inclined from the meridian, the first eight points, and diminished again as her head approached the meridian the other way.

After rounding the Cape of Good Hope; in proceeding to the northward the aberration constantly decreased, and in Bombay Harbour, with the ship's head either east or west, there was only one point aberration.

On coming to the southward again after leaving Bombay the aberration constantly increased, was 3 points again off the Cape of Good Hope after rounding which, it gradually diminished as I proceeded to the northward. On arriving in the River Mersey, the compasses all agreed within of a point, and the pilot found them to be correct by his bearings. On the 2nd voyage the compasses being in the same position, and nothing further having been done to them whilst in Liverpool, the very same results again occurred. For from leaving Liverpool the binnacle compass kept gradually deviating from the others, as I advanced to the southward, and, as before, attained the greatest deviation in the highest southern latitude. In going to the northward towards Bombay it deviated less and less, and in Bombay was the same as last voyage. Coming to the

southward, again towards the Cape of Good Hope, it as gradually increased, and decreased again in going to the northward, till now in lat. 49° N. there is no sensible difference between the compasses.

Hence it appears that this deviation regularly increases, the farther I get from the latitude of Liverpool, (where there is none,) and it seems matter of curious conjecture, when the greatest deviation would take place. I imagine the cause to be the vessel's iron stern, iron bulwarks, tiller, and wheel chains combined, acting on the binnacle compass alone, and not on the other two compasses. I may here state that the Richard Cobden is a flush vessel, except a break of about 3 feet to the forcastle deck. Also, that her bulwarks are iron, waterways also, that her stern is circular and overhangs considerably, and the tiller is a strong thick piece of iron.

The question arises, why should all the compasses agree in Liverpool, and not in another latitude. It is evident that the antagonist magnets placed by Mr. Gray, fully answered their purpose on the whole of the compasses, in the latitude they were corrected for, and on two of them in all latitudes. But why should not the third compass also in all latitudes? And, what unknown power is it that causes this deviation in the third compass, which was corrected at the same time, and under the same circumstances as the other two?

In putting these facts on paper, I trust they may meet the eye of some one, who can account for them satisfactorily; they may also, perhaps, serve remotely, as data for the investigating the magnetic intensity of different latitudes. In my log book and journal I have noted every day the amount of aberration on the course then steering; but, this has never been the maximum amount of the aberration unless when the ship's head has been near east or west.

The science of Magnetism is so interesting, and the laws that govern the phenomena so little understood, that it becomes all those who witness any singularity in effects resulting from its agency, to bring them forward, not only for the advancement of the science considered theoretically; but, also on account of the great value, that a correct knowledge of it would be practically, now that iron ship building is so much entered into. These were the motives I had in view in sending these lines, and trusting you may not find them too prolix, if you do pray dock off the fag ends.

I remain, &c.

T. LIDBETTER,
Commander of the "Richard Cobden".

To the Editor N. M.

ON THE WANT OF A BOARD OF EXAMINERS AT BRISTOL.

Bristol, Jan. 13th, 1848. SIR.-I see in one of your notes in your last number of the Nautical Magazine, that you say (in speaking of the examinations of Masters and Mates,) "We would merely ask them would it injure your reputa

tion as seamen and navigators by the possession of a warrant of your fitness"? I answer no, but quite the contrary; now, there are several of us would be happy to pass, but I will state why we have not done so, the expense is too great, as there are no examiners nearer than London.

I have just returned from a voyage to the West Indies of three months and two weeks duration, the pay is £4. per month, now it would take at least £5. to go to London, pass the examination and back: so it would you see, Sir, take rather more than a third of my pay, and as the majority of the Masters and Mates out of Bristol are married men with families, and nothing to depend upon but their pay, I think you will see we cannot afford it. I think, Sir, as there are so many ships out of the Port of Bristol, we ought to be favoured with a Board of Examiners here as well as at Dundee, &c.

If it is not trespassing too much on your kindness. Sir, perhaps you will mention in the your next number of the Nautical Magazine, whether it is likely we shall have a Board of Examiners at Bristol or not, and you would much oblige us all by so doing.

am, &c.,

A BRISTOL MATE, AND A CONSTANT SUBSCRIber.

To the Editor N.M.

[We give the above letter publicity with much pleasure, and with the hope that the interest that has been lately evinced with regard to the examination of Masters and Mates, will induce the proper authorities to render them every facility. We know not why the Port of Bristol should have been overlooked.

The writer, it appears, has the wish, but not the means of passing, and we trust that 'ere long Bristol will possess a Board of Examiners, in order, that his wishes and those of many others may be fulfilled.

It may be that at Bristol, there is no Coporation of Trinity House, or a Branch Board, consisting of sub commissioners of Pilotage; even the "Ballast Board" at Dublin has authority to examine Masters and Mates. We are inclined to think that the omission of Bristol must have happened from some such cause as the above, as we find upon reference to the regulations originally issued by the Board of Trade, the following note annexed; "Other Ports will be added to this list when there exist authorities competent to undertake the duty."

Our correspondent will perhaps point out what authorities there are at Bristol, who might with propriety be entrusted with this duty.-ED, N.M.]

ON THE DIFFICULTY ATTENDING THE EMBARKATION AND
DISEMBARKATION OF AN INVADING ARMY.

Royal Harbour, Ramsgate, Jan. 14th, 1848. SIR. Having received several most anxious letters on the subject of this Harbour, and the possibility of an armed force suddenly crossing the Channel, and taking it in possession, I venture to offer a few remarks; and since I speak principally of the impracticability of embarking or disembarking troops from, or at, any of our tidal harbours, and the diffi