The lieutenant and commander

by Basil Hall

The velocity with which the air drawn from beyond the tropics travels along the sea towards the equator is probably not above twenty miles an hour, a rate slow enough to allow time for the constantly-increasing friction of the earth's rotation to act upon it, and draw it more and more entirely to the east. By the time it has reached the equatorial regions, the friction of the earth's surface has operated long enough to carry the air completely along with it; and, of course, all relative motion being done away with, everything easterly in the character of the Trade-winds will be at an end.

But, although this constantly-increasing friction of the earth's rotation has thus annihilated all relative easterly motion between the air and earth, that air still retains its motion towards the equator; and accordingly we do find the Trade-winds, at their equatorial limits, blowing, not from the east, as Hadley, Dr. Young, and others, conceived, but directly from the north and from the south respectively. The strength and velocity of the Trades at these places is, in general, considerably diminished, chiefly, perhaps, by the air becoming heated, and rising up rather than flowing along; and also, no doubt, by the meeting of the two opposite currents of air—one from the north, the other from the south—which produces the intermediate space called the Calms, or the Variables.

In strict conformity with these theoretical views, the clouds above the Trades are almost invariably observed to proceed in the contrary direction to the winds below. On the top of the Peak of Teneriffe I found a gentle breeze blowing from the south-westward, directly opposite to the course of the Trade-wind.

The more detailed circumstances usually met with in that part of a voyage to India which lies between 30° north and 30° south, and which I am about to describe, will now, I imagine, be readily understood. Before setting out, however, I must strongly recommend any one wishing to see these matters clearly, to have them fixed in his mind to useful purpose, to follow both the theoretical and the practical parts of this explanation with the assistance of a terrestrial globe.

Most ships touch at Madeira, either to take in a stock of wine, to get fruit and vegetables, or to form a pleasant break in the early and most disagreeable part of the voyage. Some ships pass barely in sight of the high mountain which rises above the town of Funchal, and satisfy themselves with taking sights for verifying the rates of their chronometers when on the meridian of the island; while others tantalise their passengers still more by sweeping through the roads, without anchoring, or communicating with the shore. The captains by such ships are pretty deeply, if not very loudly, abused by all hands, passengers especially, who are perhaps the most dissatisfied, because the most idle, of mortals. Shortly after leaving Madeira, which is in 32-1/2° north latitude, a ship may expect to meet the Trades; but she cannot calculate with any certainty upon catching them till she arrives at the parallel of 28°. On first reaching the Trade-wind it will be found to blow very nearly from due east, and with this a course is easily steered past or amongst the Canaries, and thence for the Cape de Verdes. Some navigators pass within this group, others keep so far out as barely to make San Antonio; and this, I think, is considered the best route. As the ship proceeds to the southward, the wind draws gradually round from the east to north-east, and eventually to north-north-east, and even to north, at the southern margin of the north-east Trade-wind.

The position of this margin or southern edge, which in technical language is called the equatorial limit of the Trade, varies considerably with the season of the year. From December to May inclusive it frequently reaches as far as the 3rd degree of north latitude, though it ranges about 5° and 6° north. From June to November it is shifted back as far, sometimes, as 13° north, but it seldom extends as far south as 8° north. Subjects which are treated of in a series of tables showing the equatorial limits of both Trade-winds, deduced by the late Captain James Horsburgh, hydrographer of the East India Company, from the observations of 238 ships. These tables show very clearly the effect of the absence or presence of the sun in shifting the limits of the Trades, drawing them after him, as it were. The presence of the sun in either hemisphere obstructs considerably the regularity and strength of the Trade-winds in that hemisphere, and vice versâ.

The great difficulty experienced in making the outward-bound voyage commences after the ship has been deserted by the north-east Trade, for she has then to fight her way to the southward across the region of Calms and Variables. But as these Variables blow generally from the southward and westward, from a cause afterwards to be explained, it is obvious enough why this part of the homeward voyage is always more easily made than the outward passage. These southerly breezes, which are met with in the Variables, blow at times with considerable force, and greatly perplex the young navigator, who, trusting perhaps to some of the erroneous published accounts, not unnaturally reckons upon meeting the regular Trade-wind, blowing, as he supposes, from the east near the equator, not from the south; still less is he prepared or pleased to find it blowing from the south-westward.

This troublesome range, intervening between the two Trades, varies in width from 150 to more than 500 miles. It is widest in September, and narrowest in December or January. I now speak more particularly of what happens in the Atlantic. In the wide Pacific, far from land, fewer modifying circumstances interfere with the regular course of the phenomena, than in the comparatively narrow sea formed by the opposite shoulders of Africa and South America.

Calms, also, are met with in this intermediate region, or purgatory of the outward-bound voyage, and occasionally violent tornados or squalls, which in a moment tear away every rag of canvas from a ship's yards. For several hours at a time, also, rain falls down in absolute torrents. Even when the weather clears up, and a fresh breeze comes, it is generally from the southward, directly in the outward-bound navigator's teeth. He must have patience, however, and strive to make the most of it by keeping on that tack by which most southing is to be gained. It is now, I believe, generally held to be the best practice to place the ship between 18° and 23° of west longitude on losing the north-east Trade; and likewise to endeavour, if possible, to cross the equator somewhere between these two longitudes. Before reaching the line, however, the navigator will almost always be met by the south-east Trade-wind. From January to May he may expect to meet it in 1° or 2° north latitude; but in summer and autumn he will find the northern or equatorial limit of the south-east Trade a degree or two still further to the northwards of the lines.

On first encountering the south-east Trade an outward-bound ship is obliged to steer much more to the westward than she wishes to do, in consequence of the wind blowing so directly towards the equator, and not along it, as some of the books will insist on, in spite of Nature. So that if she be a dull sailer she may have some difficulty in weathering the coast of Brazil about Cape St. Roque. As she proceeds onwards, however, and makes a little more southing, the wind will haul more and more round from the south to the south-east, then east-south-east, and eventually to east at the southern limit of the Trade-wind. An inexperienced sailor, on first entering the south-east Trade, is very apt to be too solicitous about making southing, and hugs the wind much too close; whereas he ought rather to keep his ship off a little, give her a fathom or two of the fore and main sheets, and take a small pull of the weather topsail and top-gallant braces, to ensure making good way through the water. Indeed, many officers go so far as to recommend flanking across the south-east Trade with a fore-topmast studding-sail set. Although, I think, there can be no doubt of the soundness of this advice, I confess that it does require no inconsiderable degree of faith to adopt a course, which, apparently, takes the ship not directly away from her object, but very much out of the straight road. In this respect, it may be remarked that the scale of navigation on every Indian voyage is so great, and the importance of getting into those parallels where favourable breezes are certain to be met with, of so much more consequence than the gain of mere distance, that two or three hundred miles to the right or left, or even twice that space, is often not to be regarded. Accordingly, in cutting or flanking across the south-east Trade-wind, the object, it should be remembered, is not to shorten the distance, but to reach those latitudes where strong westerly gales are to be met with, by help of which five hundred or a thousand miles of lost distance are speedily made up, and the rest of the passage secured.