To the north of the Cape Verd Islands we met with great masses of floating seaweeds. They were the tropic grape, (Fucus natans), which grows on submarine rocks, only from the equator to the fortieth degree of north and south latitude. These weeds seem to indicate the existence of currents in this place, as well as to south-west of the banks of Newfoundland. We must not confound the latitudes abounding in scattered weeds with those banks of marine plants, which Columbus compares to extensive meadows, the sight of which dismayed the crew of the Santa Maria in the forty-second degree of longitude. I am convinced, from the comparison of a great number of journals, that in the basin of the Northern Atlantic there exist two banks of weeds very different from each other. The most extensive is a little west of the meridian of Fayal, one of the Azores, between the twenty-fifth and thirty-sixth degrees of latitude.* (* It would appear that Phoenician vessels came "in thirty days' sail, with an easterly wind," to the weedy sea, which the Portuguese and Spaniards call mar de zargasso. I have shown, in another place (Views of Nature Bohn's edition page 46), that the passage of Aristotle, De Mirabil. (ed. Duval page 1157), can scarcely be applied to the coasts of Africa, like an analogous passage of the Periplus of Scylax. Supposing that this sea, full of weeds, which impeded the course of the Phoenician vessels, was the mar de zargasso, we need not admit that the ancients navigated the Atlantic beyond thirty degrees of west longitude from the meridian of Paris.) The temperature of the Atlantic in those latitudes is from sixteen to twenty degrees, and the north winds, which sometimes rage there very tempestuously, drive floating isles of seaweed into the low latitudes as far as the parallels of twenty-four and even twenty degrees. Vessels returning to Europe, either from Monte Video or the Cape of Good Hope, cross these banks of Fucus, which the Spanish pilots consider as at an equal distance from the Antilles and Canaries; and they serve the less instructed mariner to rectify his longitude. The second bank of Fucus is but little known; it occupies a much smaller space, in the twenty-second and twenty-sixth degrees of latitude, eighty leagues west of the meridian of the Bahama Islands. It is found on the passage from the Caiques to the Bermudas.
Though a species of seaweed* (* The baudreux of the Falkland Islands; Fucus giganteus, Forster; Laminaria pyrifera, Lamour.) has been seen with stems eight hundred feet long, the growth of these marine cryptogamia being extremely rapid, it is nevertheless certain, that in the latitudes we have just described, the Fuci, far from being fixed to the bottom, float in separate masses on the surface of the water. In this state, the vegetation can scarcely last longer than it would in the branch of a tree torn from its trunk; and in order to explain how moving masses are found for ages in the same position, we must admit that they owe their origin to submarine rocks, which, lying at forty or sixty fathoms' depth, continually supply what has been carried away by the equinoctial currents. This current bears the tropic grape into the high latitudes, toward the coasts of Norway and France; and it is not the Gulf-stream, as some mariners think, which accumulates the Fucus to the south of the Azores.
The causes that unroot these weeds at depths where it is generally thought the sea is but slightly agitated, are not sufficiently known. We learn only, from the observations of M. Lamouroux, that if the fucus adhere to the rocks with the greatest firmness before its fructification, it separates with great facility after that period, or during the season which suspends its vegetation like that of the terrestrial plants. The fish and mollusca which gnaw the stems of the seaweeds no doubt contribute also to detach them from their roots.
From the twenty-second degree of latitude, we found the surface of the sea covered with flying-fish,* (* Exocoetus volitans.) which threw themselves up into the air, twelve, fifteen, or eighteen feet, and fell down on the deck. I do not hesitate to speak on a subject of which voyagers discourse as frequently as of dolphins, sharks, sea-sickness, and the phosphorescence of the ocean. None of these topics can fail to afford interesting observations to naturalists, provided they make them their particular study. Nature is an inexhaustible source of investigation, and in proportion as the domain of science is extended, she presents herself to those who know how to interrogate her, under forms which they have never yet examined.
I have named the flying-fish, in order to direct the attention of naturalists to the enormous size of their natatory bladder, which, in an animal of 6.4 inches, is 3.6 inches long, 0.9 of an inch broad, and contains three cubic inches and a half of air. As this bladder occupies more than half the size of the fish, it is probable that it contributes to its lightness. We may assert that this reservoir of air is more fitted for flying than swimming; for the experiments made by M. Provenzal and myself have proved, that, even in the species which are provided with this organ, it is not indispensably necessary for the ascending movement to the surface of the water. In a young flying-fish, 5.8 inches long, each of the pectoral fins, which serve as wings, presented a surface to the air of 3 7/16 square inches. We observed, that the nine branches of nerves, which go to the twelve rays of these fins, are almost three times the size of the nerves that belong to the ventral fins. When the former of these nerves are excited by galvanic electricity, the rays which support the membrane of the pectoral fin extend with five times the force with which the other fins move when galvanised by the same metals. Thus, the fish is capable of throwing itself horizontally the distance of twenty feet before retouching the water with the extremity of its fins. This motion has been aptly compared to that of a flat stone, which, thrown horizontally, bounds one or two feet above the water. Notwithstanding the extreme rapidity of this motion, it is certain, that the animal beats the air during the leap; that is, it alternately extends and closes its pectoral fins. The same motion has been observed in the flying scorpion of the rivers of Japan: they also contain a large air-bladder, with which the great part of the scorpions that have not the faculty of flying are unprovided. The flying-fish, like almost all animals which have gills, enjoy the power of equal respiration for a long time, both in water and in air, by the same organs; that is, by extracting the oxygen from the atmosphere as well as from the water in which it is dissolved. They pass a great part of their life in the air; but if they escape from the sea to avoid the voracity of the Dorado, they meet in the air the Frigate-bird, the Albatross, and others, which seize them in their flight. Thus, on the banks of the Orinoco, herds of the Cabiai, which rush from the water to escape the crocodile, become the prey of the jaguar, which awaits their arrival.
I doubt, however, whether the flying-fish spring out of the water merely to escape the pursuit of their enemies. Like swallows, they move by thousands in a right line, and in a direction constantly opposite to that of the waves. In our own climates, on the brink of a river, illumined by the rays of the sun, we often see solitary fish fearlessly bound above the surface as if they felt pleasure in breathing the air. Why should not these gambols be more frequent with the flying-fish, which from the strength of their pectoral fins, and the smallness of their specific gravity, can so easily support themselves in the air? I invite naturalists to examine whether other flying-fish, for instance the Exocoetus exiliens, the Trigla volitans, amid the T. hirundo, have as capacious an air-bladder as the flying-fish of the tropics. This last follows the heated waters of the Gulf-stream when they flow northward. The cabin-boys amuse themselves with cutting off a part of the pectoral fins, and assert, that these wings grow again; which seems to me not unlikely, from facts observed in other families of fishes.
At the time I left Paris, experiments made at Jamaica by Dr. Brodbelt, on the air contained in the natatory bladder of the sword-fish, had led some naturalists to think, that within the tropics, in sea-fish, that organ must be filled with pure oxygen gas. Full of this idea, I was surprised at finding in the air-bladder of the flying-fish only 0.04 of oxygen to 0.94 of azote and 0.02 of carbonic acid. The proportion of this last gas, measured by the absorption of lime-water in graduated tubes, appeared more uniform than that of the oxygen, of which some individuals yielded almost double the quantity. From the curious phenomena observed by MM. Biot, Configliachi, and Delaroche, we might suppose, that the swordfish dissected by Dr. Brodbelt had inhabited the lower strata of the ocean, where some fish* have as much as 0.92 of oxygen in the air-bladder. (* Trigla cucullus.)
On the 3rd and 4th of July, we crossed that part of the Atlantic where the charts indicate the bank of the Maal-stroom; and towards night we altered our course to avoid the danger, the existence of which is, however, as doubtful as that of the isles Fonseco and St. Anne. It would have been perhaps as prudent to have continued our course. The old charts are filled with rocks, some of which really exist, though most of them are merely the offspring of those optical illusions which are more frequent at sea than in inland places. As we approached the supposed Maal-stroom, we observed no other motion in the waters than the effect of a current which bore to the north-west, and which hindered us from diminishing our latitude as much as we wished. The force of this current augments as we approach the new continent; it is modified by the configuration of the coasts of Brazil and Guiana, and not by the waters of the Orinoco and the Amazon, as some have supposed.
From the time we entered the torrid zone, we were never weary of admiring, at night, the beauty of the southern sky, which, as we advanced to the south, opened new constellations to our view. We feel an indescribable sensation when, on approaching the equator, and particularly on passing from one hemisphere to the other, we see those stars, which we have contemplated from our infancy, progressively sink, and finally disappear. Nothing awakens in the traveller a livelier remembrance of the immense distance by which he is separated from his country, than the aspect of an unknown firmament. The grouping of the stars of the first magnitude, some scattered nebulae, rivalling in splendour the milky way, and tracts of space remarkable for their extreme blackness, give a peculiar physiognomy to the southern sky. This sight fills with admiration even those who, uninstructed in the several branches of physical science, feel the same emotion of delight in the contemplation of the heavenly vault, as in the view of a beautiful landscape, or a majestic site. A traveller needs not to be a botanist, to recognize the torrid zone by the mere aspect of its vegetation. Without having acquired any notions of astronomy, without any acquaintance with the celestial charts of Flamsteed and De La Caille, he feels he is not in Europe, when he sees the immense constellation of the Ship, or the phosphorescent Clouds of Magellan, arise on the horizon. The heavens and the earth,—everything in the equinoctial regions, presents an exotic character.
The lower regions of the air were loaded with vapours for some days. We saw distinctly for the first time the Southern Cross only on the night of the 4th of July, in the sixteenth degree of latitude. It was strongly inclined, and appeared from time to time between the clouds, the centre of which, furrowed by uncondensed lightnings, reflected a silvery light. If a traveller may be permitted to speak of his personal emotions, I shall add, that on that night I experienced the realization of one of the dreams of my early youth.