« 이전계속 »
in any report that I have seen, is, the overloading of ships; yet this is one of the greatest and most important features in any act that would tend to the improvement and safety of navigation: it is indeed an indispensable condition—a “ sine quâ non,"—so much so, that if we do not attend to it, all our efforts will be vain and fruitless.
I will relate some two or three instances, among many that came to my knowledge on that head.
Some years ago, a brig belonging to Sunderland, came to Cardiff to take a cargo of iron. She was only eighteen months old-her measurement, per register, was 237 tons; she took 463 tons of iron, within 11 tons of double her registered tonnage. She met with bad weather in the Bristol Channel, beat about for a few days, and put into Swansea in a sinking state. She was so much strained, that all her trenails had started. She had to unload and repair, but she was never after that a sound vessel. Another case is that of a ship of 700 tons register, coming into the same harbour, at the same time, to get a cargo of coals for Aden. She took 1,300 tons, went to sea, and was never heard of afterwards.
I could give you cases of that kind, almost ad infinitum. Let any one go out as far as Gravesend, - let him inquire on board of some hundred or more vessels moored there, the difference between the registered and the real carrying tonnage, and he will to a certainty find a difference of from 50 to 100 per cent.
A new way of measuring the tonnage of vessels should be adopted:the old and new measurements are exceedingly defective, and do not even give any approximate idea of the capacity of vessels; indeed, the new is, if possible, worse than the old system, they are only calculated to cheat pilot, tonnage, and light dues. What is the use of measuring a ship, if it is not to ascertain how much she can carry ?--As it is done now, it is a farce. I could dame many, very many vessels now at sea, with cargoes double their registered tonnage. Any man in his senses must know that they must be overloaded, or the measurement be defective. Now it happens, that he would be right in both cases; everybody out of Bedlam must see that a cart built to carry two tons of goods, though it may take four tons on a very smooth and good road, will break down when it comes to ups and downs and ruts;—so it is with a ship; it may do very well in the London Docks, but at sea, there comes the rub, — in foul weather, close reefed, or on a lee shore, she is in for it, and cannot get out of it, because she is overloaded.
The old continental way of taking the measurement was the best after all, but, like every thing else, they have changed it for the worst; nothing was more simple, and it gave the exact power of the vessel. You had only to take the length on the deck from inside the stem to the stern post, the breadth inside amidship, the depth under deck to the floor. Multiply these three, one by the other, and divide the quotient by 94. I have tried that method in more than fifty instances, and found that it was within a ton, and often the fraction of a ton, what the ship would carry in sorted goods, or casks; and if we put five per cent. more for heavy goods, we have the very weight she can take without being overladen. I remember the time when insurance offices would not pay for losses of vessels loaded over that ratio, and there were less wrecks then, than now.
We hear of vessels to be sold, stowing large cargoes and sailing without ballast: these very recommendations are their ruin. I maintain that a ship should have at least one-third of her tonnage in ballastthat she is not fit to go to sea and carry her canvass in safety, without; half would still be better, and there should be a regulation to this effect. Ballast-stations could easily be got in every harbour, either to take or unload the ballast. Captains should be made to conform to it, or be punished if they do not. There should be a ballast manifesto as well as a manifesto for goods, and the pernicious practice of throwing overboard ballast at the mouth of rivers and harbours, or on the roadsteads, should be visited with a heavy punishment. Much more remains to be said on the matter, but I must not encroach too much on your valuable columns.
DESULTORY REMARKS ON THE TRADE Winds.-By Argonaut.
A Supplemental Chat.
THE constancy of the Tropic Wind is so remarkable that it has engaged attention from the voyage of Columbus to this day. Philosophical writers have endeavoured to search out the cause, but none have afforded a more reasonable and clearer view than Dr. Halley, whose theory has generally been received as the true one.
There are, however, breaks occasionally in the regularity of these winds that are rather perplexing to account for. The Sun, or its influence, connected with the diurnal rotation, it cannot be doubted is the main cause of this grand movement of the air, of its constancy, and of its seasonal variation in direction. I would be understood not to subscribe to the theory of the earth's rotary velocity having any mechanical effect on the air; inasmuch as the diurnal motion of the earth on its axis, shifts the points of greatest rarefaction more and more westerly, it is operative and in that way alone.
Causes are secondary it is true, in any consideration of phenomena; but the mind does not rest satisfied alone with the classing of facts which are to form a registered system of the aërial currents of the ocean; the desire is active to complete what observation and experience point out, by linking cause with effect, albeit the reasoning power is often at fault.
The seasonal changes in the direction of the trade winds from being coincident with the sun's place, no doubt are attributable to that cause.
The learned Humboldt has said that, in the summer “when the sun entering the northern signs, rises towards the zenith, the breeze from the N.E. softens and at length ceases; this being the season at which the difference of temperature between the tropics and the continuous zone is least.” He also states that the north polar supply of air ceases during this season.
With every respect for such high authority, I cannot chime in with this opinion if it be meant to be taken literally. It seems to me that, the design of the process is, a change of air; and that there can be no suspension of that process whilst rarefaction goes on; which, there can be no doubt it does throughout the year. It is true that there exists but little difference at this season, between the temperature of the Temperate zone in continuity with the Tropic, but the effect would be, and indeed is according to observation, merely a lessening of the force of the N.E. trade wind.
According to the philosopher's words, a general calm must ensue, which we know is not the case. By the same parity of reasoning by which we account for the flagging of the N E. Trade wind in summer, we arrive at the cause of its activity in the winter; but, the process of intermixture of airs is, I believe, carried on, principally, independent of wind.
Let there be ever so little difference in the temperature between the air within and without the tropic, the mixing will go on, and it is perpetuated, and regulated on one side by the amount of rarefaction, and the density of the atmosphere on the other side nearer the pole.
The mean lateral limit of the N. E. Trade wind* towards the equator is greater in winter, and less in summer; that is to say: the wind extends to about the 8th and a half degree north from April to August; and from November to March to about the 5th degree north.
But variations occur in these limits in different years; the difference of three and a half degrees between the summer and winter limit cannot therefore be relied on, the changes being regulated by causes which we cannot calculate upon; but, however complicated and inexplicable these may appear to us, we may safely believe that the natural system is perfectly regular.
The phenomenon of the S. E. trade wind over shooting its hemisphere and pushing on from two to five, and occasionally many more degrees north of the equator is very remarkable. What are the causes? The radi of the parallels are said to be greater in the south than in the north; and the sun is a trifle longer in the northern signs. Can these operate? Probably but little.
The presence of the equatorial current may be an assisting cause; and I think it by no means chimerical to infer that, the remarkable circumstances of the barrier of ice in the southern hemisphere being ten degrees of latitude nearer the equator than the belt of ice in the north is, may be an agent in the prolongation of this wind across the line.
* Of the Atlantic.
From the information of a friend, a naval officer, I find that, when homeward bound, on the 1st of November 1826, he carried the S.E. trade wind to 70° 30' N., in longitude 24° W. The wind then became variable with intervening calms, until the 6th, when he experienced N.E. and E.N.E. breezes to the 12th. The wind on that day changed to S.E., vacillating more easterly, and then veering to S. E. and south, up to the 16th in lat. 16° and long. 29o. After which the N.E. trade became steady. On the 14th the S.E. wind blew strong, with a heavy sea running! On the 20th, in 23° 10' and 33° 46', the wind came from the westward, and so continued until the 24th, in 28° 58' and 29° W., when it veered to N.N.E. The change of wind to the west had no effect on the barometer which was at 30:30; but it fell during the night of the 21st, when the wind blew in heavy squalls, and rose as the wind veered to the northward.
These mutations in the regular course of the N.E. trade whether we account for them from local causes acting on different strata of the atmosphere, or otherwise, appear as clear proofs that the velocity of the earth’s rotary motion can have no mechanical effect on the air. The same officer, outward bound, in 1824, in May, carried the E.S.E. wind from the equator to 20° 02' S. and long. 38° 11' W. about two degrees from the Brazillian coast, when it veered to N.N.E. and continued to 30° S. and long. 46° W. The wind then came from the N.W., shifting to the south, and round again to the northward.
At the season of the year the wind is generally from the southward of the east point*; the instance given is therefore remarkable, and probably owed its origin to local causes; it is curious, inasmuch as the air was in motion from a lower towards a higher latitude, contrary, apparently, to calorific theory. In all such irregularities, it is desirable that in the progressive run, the state of the thermometer be regularly noted; the topt is a better place than the deck for its suspension. This northerly wind, it appears, was steady for 600 miles, flowing in a direction parallel with the general trend of the coast. How was the current running at the time? It is not mentioned; but here it is said to run with the wind. I am of opinion that currents often give a direction to light winds, the courses of which previously to reaching the current run towards, a different point.
Suppose the E.S. E. trade to approach the Brazil coast gently flowing, in reaching this implied current to the southward, it will turn from its E.S.E., course, and follow that of the water stream; so that the popular opinion is reversed, and reasonably, because it is not likely, unaided, that light wind would propel water into a stream; or turn it if flowing, in an opposite direction; a strong wind may turn it aside; but weak or fresh, alone it creates only a drift.
The seasonal changes in the direction of the S.E. trade wind may be
* What is called the southerly monsoon of the coast.
† Because there is less of the local atmosphere of the vessel or of radiation from the decks, &c., to affect the instrument.
attributed to the sun's place. The drift current from the open ocean meeting with the resistance of the coast will be turned one way or the other; for, the water pressed onward will seek its level; in this case, the prevailing wind becomes operative, and the repelled water will go with it either to the southward, or the northward, according to the season. But, in the other instance, it was the season of the southern "monsoon,” as it has been, perhaps, not very correctly, termed, when the northerly coast set is said to be established. If that was the fact, the current must have been running in opposition to the local N.N.E. wind; but I have assumed that, the stream was still running to the southward and so drew the wind with it. Of course no decision can here be given; but what I have said will show the propriety of seamen noting the direction of current as well as wind that the truth may be arrived at. Had the wind drew round to the northward from a more eastern quarter during the night only, then we might have hazarded a conjecture of the cause being the result of two contrary winds, the easterly from the ocean, and the westerly from the land; but it continued steady throughout for a distance of 600 miles. Calm is also often induced between the limits of the ocean breeze and the land-wind; and near islands the process of the renewal of the sea breeze is extremely curious, as if the land-wind had the effect of an opiate; in the evening, the Tropic wind gradually “goes off into a sound nap,” in the morning, as though refreshed by its slumber, the air nearest the land begins to bestir itself, to breathe gently, and, crab like, “backing astern”, until the potent power that rules it, having attained a few degrees of elevation, re-asserts its influence, it rushes in with a voice of gladness, dispensing its blessing far and wide.
To account for this N.N.E. wind, out of season, is not indeed an easy matter, but it is possible that during the rains (which set in in April) to the northward, the air had been greatly lowered in temperature by electrical discharges, and the increased activity of evaporation, whilst warm dry weather was prevalent to the southward, and rarefaction busy, hence a movement would follow from the lower to the higher latitude, so that the reversal of the ordinary course of operation would, as hinted, be only apparent. Some such cause probably occurs to create the Brazilian wind from the S.W., known by the local name of “Rebojos.”
The old idea that wind always followed a rectilinear course is giving place to a new theory, the curvilinear. It is not, however, to be understood that the wind does never follow a straight course, but that it is often found to flow in a curve. Some of its movements are indeed very perplexing, as the causes are not cognizant to the senses: take, for instance, the often occurring phenomenon of its pendulum-like action, commencing at 1, veering regularly to 2, 3, 4, 5, and so on, and then as gradually returning from the last point to the first! As a single principle, or agent, calorific influence, so governing in ordinary cases; seems, as far as our knowledge and intelligence act, utterly inoperative.
The capriciousness of aërial currents, which has become a proverb, is a design; the result springing from their inconstancy in the extra-tropical regions of the earth, impresses us with that conviction, though we
NO. 2.-VOL. XVII.