Memoirs of Service Afloat, During the War Between the States

by Raphael Semmes

“Dear Sir:—I have received your several letters from Philadelphia. As a rebel privateer has burned several American ships, it may be as well if you can have your bills of lading indorsed as English property, and have your cargo certified to by the British Consul.”

Such nice little missives as these, written from one city of “grand moral ideas,” to another city, whose ideas were no less grand or moral, quietly instructing ship-masters to commit perjury, were of great assistance to me, when, in the classical words of the New York “Commercial Advertiser,” I had a “Yankee hash” to deal with.

On the 29th of March we crossed the equator. The event is thus recorded in my journal: “Crossed the equator at five P. M. in the midst of a dense rain-squall, with lowering, black clouds, and the wind from the south-west. We were in chase of a sail at the time, but lost her in the gloom. It rained all night, with light airs and calms. We have experienced a south-easterly current, setting at the rate of a knot and a half the hour, for the last twenty-four-hours.” We made our crossing a little farther to the eastward than usual—26°—on purpose to counteract the Yankee dodge spoken of a little while back. We now encountered a variety of currents, some setting to the south-east as just mentioned, others to the east, others to the south, until finally we fell in with the great equatorial current setting to the westward.

The study of the phenomena of the currents, is one of the most interesting that can engage the attention of the marine philosopher. We have already had occasion to explain the circulation of the atmosphere—how the wind “cometh and goeth,” not at random, but in obedience to certain well-defined natural laws. The circulation of the sea is no less regular than that of the atmosphere, and has equally important offices to perform. If the sea were a stagnant mass of waters, some portions of the earth which now enjoy temperate climates, and teem with millions of population in the enjoyment of an abundant fauna and flora, would be almost uninhabitable because of the extreme cold. Some portions of the sea would dry up, and become beds of salt, and others again would, from the superabundance of precipitation, become fresh, or nearly so. In short, there would be a general disturbance of the harmonies of creation. To obviate this, and to put the sea in motion, various agencies have been set at work by the great Architect; chief among which is the unequal distribution of heat over the earth’s surface. We have already called the sun the Father of the Winds; he is equally the father of the currents. The warm water of the equator is constantly flowing off to the poles, and the cold water of the poles flowing back, as undercurrents, to the equator. This flow is not directly north, or directly south, but by a variety of tortuous channels. The different depths of the ocean, the obstructions of islands, and continents, clouds and sunshine, and a great many other agencies, combine to give this tortuosity and seeming irregularity to the currents.

Let us take an example. The Alabama has just experienced a south-east current in a locality where the current sets, as a general rule, to the westward. How are we to account for this? It may be due to a variety of causes, all working in harmony, however, with the general design. In the first place, it may be a counter-current going to fill the place left vacant by some other current; for, as a matter of course, when a given quantity of water flows away from a place, the same quantity must flow back to it. Or it may be a principal, and not an accessory current, set in motion, say by heat. Let us see how easily this may be accomplished. Suppose a dense canopy of clouds to overshadow some considerable space of the sea, for a day, or it may be, for a few hours only. Whilst the rays of the sun are shut out from this space, they are pouring down their heat with tropical fervor, say to the south of this cloud-bank. Under the cloud-bank the water is cooling, beyond the bank it is being heated. Under the bank evaporation has ceased almost altogether, beyond the bank it is going on at the rate of about an inch in twenty-four hours. Here are powerful agencies at work, changing both the temperature, and specific gravity of the waters.

Waters to be at rest must have the same temperature and specific gravity. These waters therefore cannot remain at rest, and a current is the consequence. To-morrow, perhaps, the process will be reversed, the cloud and the sunshine changing places, and the current flowing in a contrary direction. These are local disturbances of the system of oceanic circulation—little venous derangements, as it were, the great arterial system not being materially affected by them.

There are other exceedingly beautiful agencies at work, on a smaller scale, to disturb the oceanic equilibrium, and set the waters in motion. It has puzzled philosophers to account for the saltness of the sea. Whatever may be its cause, it plays a very important part in giving vitality to its circulation. If sea-water were fresh, evaporation would not produce any change in its specific gravity. One element of motion, therefore, would be wanted. But being salt, and the salts not being taken up by the thirsty air, in the process of evaporation, every rain-drop that is withdrawn from it, helps to put the currents in motion.

But these are surface operations; let us dive beneath the surface, and witness some of the wonders that are going on in the depths below. We have before shown the reader, the coralline insect, that wonderful little stone-mason of the sea, which, in the hands of Providence, is the architect of islands and continents. The sea-water is the quarry from which this little toiler extracts his tiny blocks of masonry. If the water were fresh, it would not hold the materials in solution, which he needs for his work. But being salt, it has just the materials which he needs.

But how does he affect the currents? the reader will ask. As follows: Every particle of solid matter that he extracts from the sea-water—and he must have limestone to build those islands and continents of which he is the architect—alters its specific gravity. The little globule of water, from which he has just taken the block of stone that would be scarcely visible under a powerful microscope, has become lighter than the surrounding globules, and ascends to the surface. In obedience to the law which we have mentioned, that as much water must flow back to a place, as flows away from it, a globule of water from the surface now descends to take the place of that which has arisen; descends to the little stone-mason, that he may rob it, in turn, of the block of stone that it contains. The globules of water thus become the hod-carriers for these little stone-masons, working away, in countless myriads, at the bottom of the sea.

But what becomes of this lighter globule of water, which has arisen to the surface, because it has been deprived of its solid matter? It must flow away somewhere in search of the salts it has lost, for if it remain stationary, in course of time, the sea in its neighborhood will all be deprived of its salts, and there will be no more globules to descend to the little stone-mason. But when the globule starts to flow off, a current is established.