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should fail in discovering the causes. The sun has been called the “god of the day”; it is also the god of the winds, but it has many subordinate agents in its service for the promotion of aërial agitation, and none perhaps more accessary in the government, than electricity.
Within the tropics wherever large islands lie in groups, they often influence the direction of the wind; but, calms are still more puzzling than the fluctuations of wind. What cause can be assigned for a column of air being in a state of quiescence between two opposite winds? Or, still more curious, a circle of calm in the heart of the trade wind! I have run with the trade wind (in the West Indies) gradually declining in strength, until the air became motionless, at least, apparently so; in a certain time after, a fresh breeze from the west pushed into this column of quiet air, and—What? Imparted to it a motion! That is questionable. What then drove the whole body to the eastward, merely causing it to shift its position, whilst the western stream of air pushed into its place! Who can decide? If another ship had been to the eastward, and we could have got a sight of her log subsequently, we should be better prepared to answer the question.
It may seem ridiculous, but some insight into these curious and interesting matters, may be gained by (under similar circumstances) ships chasing the wind! Had I been independent and could have ran back with this (temporary) west wind* on the same line, I had come, I should have found out what became of the calm, and whether, the trade wind fell back, as the blustrous west advanced its opposition to the east, or stood a “brush."
Had they been both of the same strength and met, what then? Greek against Greek! "and the tug of war!” Even, so, probably, a gale, with a strong tendency to a circular motioneri electricity forming the ring, whilst the helpless calm would be shut up in the centre, as in a glass case, and the very genï would be weeping for joy! This would be, we think, very like an insipient hurricane.
In these aërial contests, as, sometimes, in gladiatorial combats, the stronger, though prevailing for a time, ultimately, from exhaustion, yields to its weaker opponents.
The interloping west wind I have spoken of, after a brief bluster, and a scowl that was enough to create alarm “beat its march back," but how far it had pushed its advance, I cannot say, it, however, began to breathe short, as the fancy would say, became “ winded;" which symptom no sooner showed itself, than the old trade, peeped in side ways, and finding its opposer at the last gasp, gained “pluek," and so threw in “right and left” (variable squalls), and after occupying an hour or two “crowing" over the defunct, came sliding in, and whistling its usual tune, as complaisantly as if nothing had happened to interrupt its wonted equanimity.
I have often laughed at the idea of how close a resemblance may be made between these aërial doings, and the actions proceeding from the capricious workings of the human heart! This strain may be very undignified, and very poor philosophy, true it may be; but, it is more, it is true.
* It could not have gone far, as it lasted but a short time.
“ Philosophy is not science," so it is said; I have nothing to do with the question: what I wish, and have a great desire to see, is, the practical seaman of deep thought, habitually become observant of natural phenomena; and not only record the facts, but state his opinions freely, a single good idea may sometimes be found among much matter that is of little value, and thus without any pretensions to subtilty in science, he may be useful to it.
I am in this chat, merely skin ming the surface here and there with hasty wing. But, to proceed:
The variations in the northern limit of the N.E. trade of the Atlantic are inferred to be consequent on the sun's place: but even in one season there are variations in the general line. The received opinion is that, when the sun is in the southern signs the general line is about the 27th degree north; and, in the reverse season it reaches as high as the 30th, and 32nd degrees. It would seem, however, that the variations of this line, are not solely influenced by the sun's place, for, if the luminary alone acted, the general line would change with regularity, which is not the case.
Two ships crossing the tropic under the same longitude, one a year after the other, on the same day of the month, will find a difference of one, two, or three degrees of latitude in this line; and two vessels crossing southerly, but under different meridians, in the same day, will meet with the settled trade in different parallels; but there is not a doubt that the sun has a governing influence on the extension of the action of this wind in the different seasons. I have as little doubt, too, that the general character of the atmospheric temperature of the Boreal regions has something to do in the process, but even in that we must fall back upon the sun and the seasons.
There is a belt northward of the tropic of Cancer, and southward of the latitudes, wherein the westerly winds are prevalent, which has been termed by seamen “ The Variables”, being a sort of neutral space between the N.E. trade and westerly winds. Within this belt the temperature varies little from that of the tropic line, and calms, and light fluctuating breezes are therein prevalent. These features seem to be derived from the position of the space being intermediate of the two winds moving in opposite directions; and the local atmospheric changes going on within it, must in some degree influence the bordering currents of air on either side, perhaps this may give a clue to the local variations which occasionally occur in the northern line of the trade wind.
Another remarkable circumstance is that, the trade winds commence at a certain distance from the western face of the continents, between which and the starting line, there are westerly, and cross winds; along the western line of South America it is well known that a southerly wind exists.
In the Great Ocean (by no means a "Pacific” one) there are also
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 matation 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 flag. ging of the wird 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 Aowing 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. 49o N. Long. 16° 30' W. Str.-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 binnaele, she took 131 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 390 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 binpaele 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 Boinbay was the same as last voyage.' Coming to the