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merchants of Europe it would give ours two voyages to one. There is scarcely a region in the limitless South Sea, with which a trade would be lucrative, that could not be reached by them in halt the time that would be consumed by English, French, Spanish, Dutch, or Swedish navigators. - If,” says Mr. Scarlett, “ this scheme were realized, it has been calculated that the navigation from Philadelphia to Nootka Sound and the mouth of the Columbia river, which, by Cape Horn, is now 5000 leagues, would be reduced to 3000 only!” In fact, the reduction would be greater. But at this rate what would the reduction necessarily be as regards the navigation in that direction from New Orleans, Mobile, St. Augustine, Savannah, and our entire southern seaboard? The interchanges of commodities between our great and teeming valley of the West, and the rich and rising regions of the Pacific, would be accomplished almost at the mouth of the Mississippi.
Nor can securing, in this way, for our own country, the just benefits of her relative position be made the subject of complaint by other nations. We do not propose—at least I hope not—to monopolize the uses of the canal; on the contrary, it would be thrown open on terms, if not of equality and freedom, of the utmost liberality. “Although an artificial structure, reared by the money and policy of our people, I would give it the unchangeable character of a public highway of nations.
G. M. DALLAS.
REMARKS ON SURFS, ON ACCUMULATION ON WAVES, AND ON THE
REVERBERATING ACTION OF OCEANIC WATER.
As your valuable Magazine combines such a host of knowledge, and useful information one can never be tired in reperusing articles that have come under their notice before. I for one am ever anxious to improve, I am again threading my way through your volumes, and must be pardoned for going so far back as 1837, in which will be found p. 441 an interesting paper on the surf at Nice.
As the above are subjects of such vast importance and deep interest, and embrace points which have hitherto been little considered, they admit of some brief observations in reference to the note added to the article I have mentioned, supplying Mr. Webster's original theory of the rollers.
It is a point scarcely disputable that the equatorial current in its oblique course across the South Atlantic towards Cape St. Roque, the north-east angle of South America, receives the drift waters pressed thither by the south-east trade wind, and that the accession, although comparatively trifling, may serve to augnient the volume, though it should add nought to the velocity of that great stream. This oceanic river which passes round the elbow of the continent, in conjunction with the alternating inshore currents preserves the level of the ocean there from an
undue elevation, by carrying off the superfluous supplies as fast as these are pressed onward by existing causes, distributing and returning the amount by circuitous routes.
This view is taken not alone from the disposition of the land, the ocean, the winds and the currents; but also from the consideration that, the latter generally are designed to fulfil certain purposes in the economy of nature--the effecting a constant interchange of waters, and the preventing accumulation and preserving a general level, and that, the operation is perfect.
Admitting, the principle of the theory, which is extremely reasonable, the re-action seems to be a consequence of the constant pressure upon the fluid, occasioned by the maximum strength of the trade wind during its greatest height and regularity, declining in the season when its minimum force succeeds to that, and its constancy becoines interrupted by calms and contrary winds.
That the waters occasionally flow back* in a wide extended stream there is no disputing, but this action does not appear to be the effect of accumulated waters upon the coast from the trade wind drift re-acting, as will be shown, therefore the immediate cause of the periodic return of the rollers on the islands alluded to in the note, is, the reverberatory motion if the incumbent waters en masse, irresistible truly, but easy and rapid, and as an action probably unseen or unnoticed in the open ocean unless meeting with sudden resistance; in other words the return merely of the impressions created by the trade wind without necessarily any flowing or streaming; and if this and the perfection of currents be ad. mitted what need have we to insist upon an accumulation of water on the western coast?
The spherical form of the moleculæ of the water, and the active prirciple by which these are constantly striving to acquire an equilibrium, whenever there may be undue force, would ensure the re-action as soon as the fluid became relieved from the unequal pressure; this re-action is inevitable, but it does not necessarily follow that there should be an accumulation of water for its fulfilment, upon a long line of coast open to the free ocean, whatever cause may press the surface waters towards that line, could not, I imagine, possibly create an undue accumulation of water there; the nature of the fluid and the activity incessantly exerted in relieving itself of the action of unequal pressure, would prevent it where there is no obstacle to impede its energetic impulse. Besides, in such an extent of ocean, as we are speaking of, the lateral pressure required to raise the mass of waters, independent of the moon's attraction, upon the coast, (if there were no intervening cause to prevent it,) of the western land, even only a few feet, would be tremendous, and far exceeding any effect the wind is capable of producing in that quarter.
A great mass of water, such as the South Atlantic, acted upont by the constancy of a brisk wind for a given time, would swing back, as it
* It is not improbable that this takes place, annually in the wet season.
† We do not here allude to accumulation, but to the undulatory impression which on its subsidence would impart a reverberatory action to the mass.
were, heavily from its specific gravity, but not impetuously, though with rapidity, from its great expansion, and from the attractive and repulsive forces of its particles; and not improbably also, from a certain degree of elasticity, to regain the first law impressed upon it by nature, the moment it became relieved, and this with a certainty that no obstacle could effectually check.
The easterly current which has been experienced near the line in the rainy season, may probably arise from the vast body of waters ejected from the mighty Amazon and other rivers, and which from the impetus acquired by their descent to the ocean, may have the power of turning the equatorial current to the “right about” the point of contact being about 40 or 50 miles only from the coast; or, if the velocity of the combined land-streams could not effect that, which from want of depth, perhaps, would not be accomplished, the fresh water from its less specific gravity might readily pass over it, and be aided in its course by the prevailing local monsoon, or by westerly winds, which are likely to blow from the land, at that period, toward the heated air over the ocean.
This operation would take place between June and November, and if we were to look to the new current as a cause of the rollers* at Ascension, there would be no re-action in the proper sense of the word, but a direct pressure from the streaming of the waters to the eastward. This, according to my ideas on the subject, is the only way any thing like an accumulation of water could take place on the coast of the continent, because the equatorial current as a flowing line breasting the coast must receive all accessions from the eastward, and so prevent these reaching the land; and even that accumulation would be but trifling, as the rapidity (between 60 and 70 miles in the 24 hours) is too great to allow much of the supply to spread along shore, the great mass being pressed directly towards the offing by the continued descent of the fluid accessions from the mountainous districts.
During the course of my experience at sea, I have often had opportunities of observing the action and re-action of the waves upon a coast; but the idea of the rollers being caused by the latter never struck me, although the reverberation of the impression was plainly perceptible and remarked, as returning in opposition to the successive advancing undulations.
Hence may we not infer that, upon a large scale, when no obstacle impedes the duration of the return of the impression it would be continued to an indefinite extent, until exhausted, or counteracted by land?
Referring to the Atlantic rollers, the re-action would probably be in the direction whence the direct motion originated; in this instance it could not be expected to be towards the north, not, however, from any opposition to its free course that we might suppose it would meet with froin the north-east trade wind on the other side of the line, as we are assured, from occular proof, of the extraordinary phenomenon of waves proceeding directly in the "wind's eye,” but rather from the consideration
* The season does not agree with that of the rollers. NO. 3,- VOL. XVII.
of the unerring principle of the fluid which unceasingly urges it to attain, and whenever unopposed, to preserve its level.
The retrogade action of the impression upon the mass of waters south of the line, would strike upon the coasts of Ascension and St. Helena, with a trifling priority as to time at the commencement, on the former, which seems agreeable with fact. But, if the rollers, on any coast, are occasioned by direct action upon the ocean of distant gales, (and I see no reason against such within certain limits,) it is not unreasonable to conceive that, the transmission would be greatly prolonged, if the wind blew towards the point followed by the tidal wave.
In gales of wind, which last but a few days, although violent, it may be admitted, perhaps, that the undulation would not be felt at a remote distance; although, if waves really travel at the rapid rate assigned to them, without calculation, one would probably be deceived in estimating the distance they would reach in a short time, by merely looking at them as they passed by; for instance:-if in a gale of two days' duration, we find the velocity of the undulations to be equal to thirty miles an hour, (and this appears moderate,) and allow one-eight for decreased energy, as they receded from the source of the propulsion, it would be found that, in the given time, the distance reached would be as great as 1260 miles! The knowledge of the actual velocities of waves for every wind in the scale, and these are not many, is a desideratum in nautical science; but it is obvious that the determining of this object should be effected in the open ocean, as well as in the vicinity of land.
The giant swell of the North Atlantic, during the continuance of the strong north-westers, reaches quite across from America to Europe, but does not break into extremely heavy surf upon our shores, probaby from its force being gradually lessened by the basal banks; on the west coast of Ireland, and the shores of the bay-gulf of Biscay, they create a great surge during the winter. After a long continuance of easterly winds in these latitudes, has the effect of re-action been noticed?
The phenomenon of billows being often experienced during calm weather at sea, has been considered as arising from gales at some distance, which have lasted just long enough to transmit the undulation to a certain distance, and no farther. This is the impression on the minds of seamen, and it is also received as a sign of an approaching breeze in the same direction; no doubt these opinions are often correct, but probably not invariably so, as it is not unlikely that, on some of those occasions, a gale may have been blowing over the particular space, and which has ceased but a short time before a ship has reached it with another wind, and became stationary from calm following.
In accounting for å plurality of waves, perhaps, the operation of currents, the irresistible impulse of the tidal force, variable winds, and sudden alterations in some of the strata of air, whereby atmospheric pressure is relieved, may serve to assist in these ideas.
Along the coast of Darien, (Atlantic side,) a ground swell at a distance from the shore rolls on towards it, but it does not break into surf upon the beaches, except where shelves and ledges of rocks line these. On observing the billows in the offing, a stranger would naturally expect to find a heavy surge lashing the shore, but the reason why this is not the case, may probably be from soundings extending to some distance off, which by offering a gradual resistance to the velocity of the undulation, checks its impetuosity, and reduces its magnitude, in accordance with the progressive diminution of depth as the land is approached, until, on arriving there, both the force or momentum and the form of the wave become inconsiderable.
At the Isle of Pines, between Carthagena and Porto Bello, this ground swell is experienced. The eastern anchorage lies exposed to it, but although entering the confined space, it does not, as might be expected, create any surf upon the broken line of coast on the main land. The western anchorage is free from it, on account of the shelter it receives from the island; but, a surf breaks continually, more or less, along the line of the main shore, westerly, from a ledge of sunken rocks, extending the whole distance of the curve, which effectually prevents landing, although a fine sandy beach presents itself to the view.
At La Guayra, on the coast of Columbia, when the air is perfectly calm, the curious spectacle of a continuous line of high surf rolling in upon the beach is observed. The succession of the billows is incessant, and the roaring noise they create is so loud as to be heard far up the valleys! People are amazed at this, to them, inexplicable motion of the waters of the ocean, under the very circumstances when they might naturally enough expect the sea to be in a quiescent state.
This violent action of the waters upon this coast cannot be attributed to reaction, from the lessening of the trade wind, as it could not be felt there, but on the shores of the islands, where no doubt it is experienced in the proper season.
It is probable, that there are several causes in succession which operate in producing this surf: Ist. From the direct pressure of the trade wind during the dry season, when it is most active. 2nd. From the action of westerly and northerly winds in the wet season, when the N.E. trade is often interrupted by those winds, and by calms. 3rd. The shifting of the current, combined with the action of the tides within a certain distance along the line of coast.
Let us recall to mind some circumstances which we have all, during our service at sea, either observed, or heard related by others. A ship, during a period of light airs, or calms, when the surface of the ocean has been unruffled, is suddenly assailed by au enormous wave, which passes by and leaves all calm again; in a short time, however, she again encounters a similar uplifting of the water, which also passes off. This extraordinary swell may be repeated several times, or once or twice only, probably according to the strength of the breeze, or the continuance of the calm which would remove her from, or retain her in one position. Much wonder has been created on such occasions in the minds of our rough tars, who, as a matter of course, began to rake up the smouldering embers of their superstitous thoughts; but, the circumstance has remained, we believe, to this day unaccounted for. May not the phenomena be