Читать книгу A Voyage of Discovery to the Southern Hemisphere - François Péron - Страница 9

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Temperature of the Sea—Saltness of the Water—Its Phosphorescence—Observations on Natural History.

UNDER similar circumstances, and at the time of my meteorological observations, I entered on a course of experiments on the subject of the agreement between the temperature of the sea on its surface, with that of the atmosphere; the results of which experiments I have made known to the Institution.

With an apparatus, such as I judged most proper for the purpose, I attempted to make, at the same time with my friend and colleague, M. Depuch, some observations on the temperature of the ocean, at great depths from the surface, and soon began to doubt the gradual and progressive coldness of the waters of the sea, in proportion as we penetrated deeper into its abyss. I shall have occasion, in the sequel, to recur again to this part of my labours. Among the most important observations on the physical history of the sea, we must doubtless reckon those whose object is to determine the relative and absolute proportion of the saltness of the waters in different latitudes, and at different depths; unto this time, however, few experiments of the sort have been made, and even these first attempts appear to me to be totally wrong in their primary principles, and not of any essential use in their results. In short, the specific weight taken for the basis of their experiments by Ingenhouz, Labillardière, and M. Humboldt, in my opinion, is a method incapable of furnishing any given rule, because of the immense quantity of animalcule, often microscopic, which breed And multiply in sea-water, and which, though themselves distinct from the salts, perhaps do not in a less degree affect the specific weight of the liquid in which they are suspended, or rather, in a state of solution, on account of the gelatinous mucus which transudes from every part of their surface, and which gives to the purest sea-water that character of viscosity which it is always found to possess.

To collect sea-water, and keep it in bottles, like Sparman, is a still worse method; the putrefaction to which these waters are liable, cannot fail to change all the constituent principles, and thus produce, as we have already said, by the spontaneous decomposition, innumerable animalculæ.

To obviate these difficulties, it was my intention to collect, in every five degrees of latitude, a sufficient quantity of sea water, 100 pounds for example, to filter it through paper, and thus determine the specific weight with the areometer of Nicholson; a very defective method, as I have before observed, but which, being only accessary to my other experiments, was so much the more useful, as the water, by filtering, would be previously separated from the greatest part of other substances not connected with it. After this first operation, I proposed to put the water into one of the alembics which we had from government, and to carry on the evaporation to the point of drawing together as much as possible all the saline substances which it might contain in solution, and then reuniting the remainder of each of these distillations, in one or more vessels, hermetically sealed, proposed at my return to confide such valuable objects of experiment to M. Fourcroy, who would doubtless have analysed them correctly. This method of investigation, independent of the exact results which it appears to be capable of demonstrating, has the additional advantage of requiring only a succession of operations very easy to be pursued even on board a ship, and it the same time to render unnecessary all those minute details of fine analysis which cannot be properly attended to in the midst of the inconvenience that is necessarily attendant on a voyage.—Unfortunately, I was compelled in this instance, as in many others, to yield to the spirit of opposition in our commander; and I should have avoided the mention of this proposed course of experiments, if it had not, appeared to me to be necessary to engage the interest of the philosopher and traveller on the subject of so curious a part of the history of the seas, and to make known to them so easy and correct a method of making similar experiments.

The phosphorescence of the waters of the ocean is another curious and interesting subject of astonishment and investigation, and which has, ever since the days of Aristotle and Pliny, engaged the attention of the voyager. However extraordinary the slight sketch which I have here given of the principal phenomena of the phosphorescence of the sea, may appear to the reader, there is not one single word that I have not borrowed from the observations of those not liable to either enthusiasm or exaggeration. It will suffice to mention Cook, La Perouse, Labillardière, Vancouver, Banks, Sparman, Solander, Lamanon, Daprés de la Manvillette, Le Gentil, Adanson, Fleurieu, Marchand, Stavorinus, Spallanzani, Bourzeis, Linnæus, Pison, Hunter, Byron, Beal, Adler, Rathgeb, Martens, De Gennes, Hierne, Dagelet, Dicquemarre, Bacon, Lescarbot, Loeflingius, Shaw, Sloane, Tachart, Dombey, Ozanam, Barter, Tarnström, Marsigli, Kalm, Nassau, Pontoppidan, Morogue, Phipps, Poutrincourt, Heittmanne, Kirchmayer, Anson, Frezier, Lemaire, Van-neck, Rhumpe, Rogers, Drake, &c. How numerous and varied are these phenomena! Here the surface of the ocean sparkles and shines as far as the eye can reach, like a sheet of silver, when electrified in the dark—there it unfolds its waters in immense sheets of sulphur and flaming bitumen; in another place if resembles a sea of milk, the extremities of which are not to be perceived. The minutiæ of these great phenomena are not less to be admired than the grandeur of the whole. Bernardin de Saint Pierre has described with enthusiasm those shining stars which seem to dart by thousands from the bottom of the waters, and of which, he justly adds, those of our artificial fire-works are but a feeble imitation. Others have made mention of those masses of fire which roll on the waves like so many enormous red balls, and of which we ourselves saw some that did not appear to be less than twenty feet in diameter. Many seamen have observed fiery parallelograms, cones of light inverted, whirling about on their points, shining garlands and luminous serpents. In some places of the seas are to be perceived sparks of fire springing from the surface; in another part bodies of light and phosphorus are seen moving on the waves in the midst of darkness. Sometimes the ocean appears as if ornamented by an immense steep of moving light, whose undulating action seems to reach the edge of the horizon; all these phenomena, and many others which I forbear to mention, however marvellous they may appear, are nevertheless incontestible. They have been many times described by navigators of undoubted veracity, and I have myself observed most of the appearances which I have described, in different parts of the seas.

How many theories have been written in explanation of these prodigies. Sometimes, the supposed spirit of the salts, the bitumen, the petroleum, and animal oils, have been mentioned as the causes of these phenomena; sometimes, the spawn of the fishes, and other marine productions; the remains of marine animals have been thought sufficient to produce these extraordinary effects: the gelatinous mucus which continually transudes from fish, zoophytes, &c. &c. are by others said to occasion such brilliant appearances. Some naturalists have admitted a kind of moving putrefaction in the superficial beds of the sea, while some have thought it to proceed from the motion of light and shade; and others have considered it as occasioned exclusively by reflection. Electricity has also supplied some celebrated voyagers with ingenious conjectures on the subject; and more recently, phosphorus and similar productions have opened a new field for new hypotheses; some have supposed these phenomena totally distinct, others have attributed them to the influence of hydrogen. In a word, there is no sort of conjecture, probable or even absurd, which has not been adopted, and nevertheless the best naturalists remain still in uncertainty of the real cause of such grand phenomena of nature.

In the physical and meteorological part of my work, I shall have occasion more particularly to discuss each of these theories, and I hope I shall easily demonstrate the futility of each of them, one only excepted. I shall here merely mention a few of the results of my experiments and long study on this subject.

1st, That phosphorescence essentially belongs to all waters; it is observed in the midst of the waves of the Mediterranean, in the Norwegian seas, those of Siberia, and those of the antarctic poles.

2dly, The phosphorescence is generally stronger and more constant between the tropics, or near the tropics, than in latitudes nearer the poles.

3dly, The temperature, almost continually higher in the equinoctial seas, seems to be the mediate cause of this difference.

4thly, The phosphorescence is greater and more constant along the coasts, in confined seas and straits, than in the middle of the ocean, and at a distance from land.

5thly, In general this phenomenon is so much the more visible as the sea is more agitated, and when the darkness of the night is more profound.

6thly, We may, nevertheless, observe, that when the sea is calm, and when the moon shines bright and clear, it does not always eclipse the phosphorescence.

7thly, All the phenomena of the phosphorescence of the waters of the sea, however multiplied, however singular they may appear, may be nevertheless deduced from one single principle:—the phosphorescence peculiar to marine animals. My numerous observations, and the beautiful collection of coloured representations of phosphoric animals, by M. Lesueur, will, I hope, place this beyond a doubt.

8thly, This active phosphorescence of animals, very different in every respect from that faint brightness produced in certain cases by putrid decomposition, is so dependent on the organization, and of life, that it increases, grows weaker, and becomes extinct with the latter, so as never to be reproduced after death.

However various my physical and meteorological observations may have been, they did not occupy the whole of my time; so many undisturbed hours may be devoted to study when on a voyage, far from the noise of cities, and entirely abstracted from all the duties belonging to family or to friendship, and even from every connection with so, tidy. The study of marine zoophytes, &c. particularly engaged my attention in my leisure hours; this bad been more especially recommended to me by M. Cuvier, whom we may esteem as the author of this classification of the animal kingdom, and whose advice and instructions served me as a rule in my investigations. My colleague, Maugé, and my friend, Lesueur, acted in concert with me, and we had the satisfaction of making discoveries of this kind, both interesting and numerous. But it shall suffice here to sketch slightly the picture of some few of these animals, so long neglected by naturalists, and which, from the strangeness of their form, the singularity of their organization, the beauty of their colours, and the variety of their character, so well merit the attention of the natural philosopher.

At the head of this class of animals I shall place the Physalis, a kind of zoophyte, which, by means of a membrane or bladder, similar to that of certain fish, floats always on the surface of the water. A kind of membraneous muscle in folds or plaits fixed longitudinally on the back of the airy, vesicle, furnishes the animal with a real sail, which it can at pleasure expand or contract, in suitable proportions to the force or direction of the wind. From this singularity, it has frequently been named, the frigate, the galley, the schooner, &c. by these names it is generally known to the seamen of every nation. This vindictive animal spreads on the surface of the waves its sinewy snares or nets, several feet in length, and of a pure and lively ultramarine blue. Woe to the hand which attempts to seize them the sensation of burning is not quicker than that of the venom which is concealed in these instruments of, prey. This sensation is attended with an intolerable smarting in the part touched by them, with a kind of numbness or stupefaction of the whole limb, such are the almost instantaneous effects of the slightest touch of the physalis. Sometimes an appearance on the skin, similar to that produced by stinging nettles, is the consequence; this is accompanied by extreme pain, which generally continues twenty-four or thirty-six hours. What can we think of the nature of this subtile poison No direct experiment has yet been made on the subject, and all that I can say from my own experience, is, that when this animal was plunged in water strongly acidulated, with any kind of acid, but especially with the sulphuric, or muriatic, the beautiful blue colour of the sinewy nets became immediately red, as if the principle of the colour was really of a vegetable nature. I ought also to add, that the poison seemed to exert a more particular stupefying power on those animals which seemed to be the food of the physalis, for it is impossible otherwise to conceive how an animal so small, could contain in its nets, and in some sort devour alive, fish of four or five inches in length, as we had often opportunity to observe. In devouring its food, the physalis makes use of a prodigious number of suckers or feelers which depend from the lower part of the airy vesicle, and which is surrounded by the venomous snares already described.

Next to the Physalis may be mentioned the Physsophoris, a gelatinous and soft species of animals, of the most beautiful colours, which support themselves on the surface of the waves by means of a vesicle shaped like a very small olive, with a thick gelatinous coat or skin, the inside of which is generally filled with air. When the animal would dive into the ocean, immediately a valve opens, the air with which the vesicle is filled is let out, the specific weight of the animal increases, and it plunges into the depths of the waters; when the animal would again rise to the surface, a new bubble of air seems to swell out, or rather to be formed instantaneously, the small reservoir is filled afresh, the valve shuts, the physsophoris again is lessened in weight, and rises again on the bosom of the waves.

In the Vellelles, the next of the class, the means differ, but the results are the same. On the hack of the animal, resembles the form of a little skiff overturned, there rises obliquely a kind of crest, extremely thin, light, transparent and cartilaginous; this is a large sail, which serves the animal to direct its motions, to alter or hasten them; always close-hauled, this beautiful azure vessel makes its way through the water, changes its course at pleasure, and rarely fails to catch its prey, which it holds fast in its numerous nets or snares with which it is surrounded, and soon devours by the help of the innumerable suckers which depend from its lower surface. The elegant shape of this animal, the transparency of the sail, the beautiful azure blue colour with which it is adorned, all unite to make it one of the most beautiful species of the class to which it belongs, and it is very picturesque to observe in calm weather, thousands of these zoophytes manoeuvring on the surface of seas, which seem like so many beautiful flotillas in miniature, directed according to the principles or our naval tactics.

In the Beroës, nature seems to have exhausted all that elegance of shape, richness of colour, and variety of motion, can present of grace and beauty. Their substance, more transparent than the purest crystal, is generally of a fine rose colour, opal, or azure; their form is always more or less spheroidical; eight or ten longitudinal, sides are disposed in a circumference, each formed by a prodigious number of small transverse leaves or folds, excessively thin, and capable of astonishing motion; these constitute the essential organs of the animal's, movements. It is with the help of these small oars, moving at pleasure, that the animal guides itself towards its prey, escapes from its enemies, whirls about on its own axis (if I may be allowed the expression); in a word, performs all its necessary evolutions. What is still more admirable in the motions of the beroés, is, that the light, being separated by the effect of these rapid and changeful motions, all the longitudinal sides become so many living prisms, which seem to enclose the animal in eight or ten animated undulating rainbows, of which language, or even painting, can give but a very imperfect idea.

How shall I be able to describe the next species of zoophyte, which like a beautiful garland of azure-coloured crystal, moves on the surface of the waves, successively raising its transparent folds, which resemble the leaves of ivy; its beautiful rose-coloured feelers are stretched oat, seeking the prey on which the animal feeds, which is no sooner caught than it is enveloped in a fatal net. This zoophyte immediately contracts itself, forming a sort of circle around the animal it has conquered; thousands of suckers, like long leeches, spring at the same instant from under the leaves which I have just described, and which in a state of repose serve to cover and protect these suckers. In few moments the prey, however large, is devoured. I cannot avoid mentioning the admirable phosphoric property so general among most of the animals of this class, and which in that I have now described, is more lively and brilliant than in others, and causes it to appear in the midst of darkness like a beautiful garland of flame and phosphorus!

In what terms shall I describe those Janthines of a purple colour, which move on the surface of the sea, suspended by a white bunch of airy vesicles! Or what can I say of those numerous legions of Salpa, of rose-colour, azure, or opal, which form banks of thirty or forty leagues in extent, and which glitter in the midst of darkness! Or of those Medusæ, equally phosphoric; which present so many singular forms in their organization, so many delicate shades in their colour! Or those Pyrosomæ, which are formed like the finger of an enormous glove, and which do not appear to have any of the organs of locomotion, digestion, respiration, or even reproduction, but which nevertheless cover the sea with their innumerable swarms. The substance of these animals is so brilliant, even in the darkest night, that it has the appearance of red hot iron! Nor should I omit to speak of the beautiful Glaucus, of a fine ultramarine blue, with a stripe of silver on the back: these resemble so many small sea-lizards, their limbs branching out in ramifications like shrubs, serving at the same time as fins and lungs: Nor of those Pneumodermæ, which the celebrated M. Cuvier (for whom I had intended several of the curious marine animals) considers as constituting a new order in the class to which they belong; these have their organs of respiration in the hind part of the back! The Hyaleæ, which abound in the neighbourhood of the Cape of Good Hope, are also a curious animal, protected only by a shell, which is extremely thin, fragile, light; transparent, and of a horny appearance. These are to be seen playing on the stormy waves of the southern ocean. As they unfold their beautiful purple fins, they might be taken for so many little tortoises in miniature, and indeed by this name they are generally called by the seamen.

Here I may be allowed to mention the discovery of the living Spirulea, which at length resolves the problem of the formation of these singular shells with several apartments, and which under the name of nummulites, belemnites, horns of ammon, hippurite, lenticular stones, turrilite, &c. &c. bear no inconsiderable part in the history of the revolutions of our planet, of which so small a quantity appear to have escaped the great catastrophes of nature, and of which species not any of the living animals have been hitherto known to naturalists.

I shall venture to speak of those azure-coloured Porpites, in the membraneous head of which species, the learned M. Cuvier thought he had discovered the type of some kinds of nummulites, with concentric spires, which are found in a state of petrifaction on the summit of the highest mountains of our continent. But I must conclude this subject; for to point out only the new and interesting objects which we collected during this long from Europe to the Indies, would exceed the bounds which I have prescribed to myself. It most suffice to add, that our collection consisted of upwards of eighty new species of different animals; and that among these is a remarkable fish, not only for being variegated with brilliant gold and purple, but also for the pustulous conic vesicles with which its teguments are bristled, and which compel the animal to float continually on the surface of the seas.