THE VOYAGE OF THE CHALLENGER.'* THE expedition of H.M.S. Challenger'
round the world for purposes of scientific research and discovery, and more specially for the exploration of the physical condition of the bottom of the deep sea, was organised by the Admiralty, as every one knows, on the strong recommendation and under the advice, as to details, of the Council of the Royal Society. It was an undertaking truly worthy of the Government of a great and enlightened nation, "foremost in the files of time," and zealous to advance human knowledge for its own sake, irrespective of what are called "practical ends," but knowing that those utilitarian results would inevitably follow sooner or later. Minor expeditions, chiefly in the vicinity of our own coasts, had previously been made at the public expense, of which some of the results have been published, such as the explorations of the gunboats ' Porcupine' and 'Lightning,' which were sent out on the suggestion chiefly of the present author, Professor (now Sir Wyville) Thomson, and Dr. Carpenter. The Challenger' is a spar-rigged corvette, of 2,306 tons, with auxiliary steam-power. She was placed under the command of Captain (now Sir G. S.) Nares, and Sir Wyville Thomson was the head of the scientific staff. She sailed from Sheerness in December, 1872, and returned to Spithead on May 24, 1876. Several partial reports of the great expedition have
* The Voyage of the Challenger' : the Atlantic. A Preliminary Account of the General Results of the Exploring Voyage of H.M.S.. Challenger,' during the year 1878 and the early part of 1876. By Sir C. Wyville Thomson, Et, LL.D., F.R.S.S. L. and E., dm. London : Macmillan and Co. 1877.
already been published, such as Mr. Wild's Thalassa, Mr. Spry's Cruise of the Challenger,' and Lord George Campbell's spirited and agreeable Log Letters.
The two volumes now before us are an instalment of Sir Wyville Thomson's more comprehensive account, containing only " The Atlantic," the exploration of the Pacific and of the great southern basin being still to appear ; and much more technical and thoroughly digested reports will one day be presented to the Admiralty, the preparation of which will require prolonged and elaborate study. The objects of the voyage may be summarised as consisting of the ascertainment of the form, depth, and composition of the bed of the ocean ; the currents, temperature, specific gravity, and chemical composition of the water at all depths, and their relation to the changes in the atmosphere ; the flora and fauna of the deep sea, and the geology and physical condition generally of such less-known islands, &c., as shall be visited. A minute account is given, with admirable illustrations, of the numerous and very ingenious instruments with which the ship was fur- nished, but these it is impossible for us to enter upon, and indeed without diagrams our description would be unintelligible. The Challenger' sailed first to Teneriffe, then crossed to the West India Islands, then north to Bermudas, and on to Halifax, then returned eastward to the Azores and Madeira, and passed down the west coast of Africa to near the Equator. She then crossed to the coast of Brazil, and recrossed to the Cape of Good Hope, visiting the lonely little group of Tristan d'Acunha and St. Paul's Rocks, thus crossing the Atlantic four times in 1873. She then entered the Pacific round the Cape, and returned to the Atlantic by the Straits of Magellan, in January, 1876, visited the Falkland Islands, and opposite Monte Video partially crossed the Atlantic again, touched at Ascension Island, and then returned home. The whole voyage was divided by " stations "for sounding and dredging, the number of which may be inferred from the fact that there were about thirty of them in the course of the first crossing of the Atlantic. During the voyage upwards of 50,000 minute meteorological observations were taken. The result of the various soundings and dredgings is, of course, enormous, and great labour must be expended before they can be all duly ex- amined and generalised. Those who care to study some of the details in regard to temperature at various depths, will find many of the facts ascertained clearly laid down in the various plates showing lines of " Isothermobaths " and " Isobathytherms," terms which, though somewhat uncouth, are self-explanatory.
The general configuration of the bottom of the Atlantic may be thus described :—An elevated table-land, averaging 1,900 fathoms from the surface of the water, extends the whole length of the ocean from north to south, half-way between the European and African coasts on one side and the American on the other. On the north it joins a transverse plain stretching from Ireland to Newfoundland, on which the first Atlantic cable was laid. Towards the south-east it approaches the Cape of Good Hope, and on the west nearly touches the north-west coast of South America, a short way north of the Equator. Thus three deeper basins are left, one, long and narrow, starting from the west coast of Europe along the whole west side of Africa. There is another near the American coast, from about 35° to 12° N.L., which is the deepest ; and a third to the south-west, ex- tending from near the Equator to about 30° S.L., and pro- bably open to the great Antarctic Ocean. The whole Atlantic may be looked on as a huge gulf of the latter on one aide of the globe, as the Pacific is on the other. The greatest depth is not more than 3,875 fathoms, and the greatest depth of the Pacific is about 4,575 fathoms. It will be remembered that a fathom is only 6 ft., so that the greatest depression of the Atlantic basin is only some 8,000 ft. more than the height of the highest mountain in Europe,—probably much less than the popular imagination has pictured it.
There is a wonderful uniformity in the nature of the sea-bottom over the whole of this vast ocean, irrespective of latitude. With the exception of a short distance round the coasts, where there is a deposit of the matter brought down by the rivers and the debris of the rocky shores, the old bed of the Atlantic, from the depth of 400 to 2,000 fathoms, is covered by what is now known as " Globigerina ooze," while at greater depth this is succeeded by a fine red clay, less calcareous in its nature than the ooze, and the whole is strewn with fragments of pumice and other volcanic products, which, however, are believed to be the result of sub-aerial volcanic action, and to have been carried out in the course of time. The " Globigerina ooze " is a very interesting substance. Its amazing extent alone, with the fact of its being almost entirely of organic origin, is sufficient to make it important, and it throws a considerable amount of light on the formation of well-known geological deposits of more ancient date. It is, in fact, the chalk formation in the course of growth. It consists, on the surface, of a creamy layer composed of little more than the shells of minute creatures of the class Foraminiferm (Globiferina, Pulvinu- line, Orbulina, &c.), with a small mixture of imperfectly under- stood things called Coccoliths and Rhabdoliths, and the tests and spines of Radialaria, the spiculw of sponges, and a few shells of Pteropods ; while living among the ooze, at least at moderate depth, are many of the Foraminiferm themselves, sponges, corals, star-fishes, and higher invertebrates, and a few fishes. Beneath this is a stratum of shells more or less broken, cemented by a calcareous paste ; and further down, a nearly uniform calcareous paste coloured grey by decomposing animal matter. It is now believed that all this is formed by the de'bris of myriads of those minute animals most of which live near the surface, while their dead bodies and shells fall to the bottom, and have been accumulating for countless ages. In examining the form and structure of these inhabitants of the deep, we must not look for the portentous and grotesque shapes which prevail among the tribes of fishes and the higher mollusca and crustacea, many of which, as the most slightly informed visitor to a museum or aquarium knows, present forms as strange and hideous as the images pro- duced in a nightmare,—" gorgons, and hydras, and chimeras dire." It requires a closer analogy to our own structure, and that of the higher animals which have distinct heads, eyes, and organs of prehension, to affect the imagination in this way. On the contrary, the structure of these little organisms, whose remains constitute so large a portion of the ocean-bed, is at once extremely simple and very beautiful. As the name im- plies, the general form of an animal of the Globigerina class is that of &symmetrical, round ball (and in some, as Orbulina, a con- geries of balls), composed of a thin and fine shell, often adorned with wonderfully beautiful carvings, covered thickly with spiculat or needles, sometimes five or six times longer than the diameter of the shell itself, delicate and fragile as spun glass. The interior of the central shell is filled with living substance, or sarcode. When you examine one of these animals microscopically in clear sea-water, and are careful not to disturb it, the sarcode is seen to exude gradually from the pores of the shell, forming a sort of fluffy fringe, filling up the spaces between the roots of the spines and creeping a short way up their length, while a more transparent living matter is drawn towards their points, up one aide and down another, with expanding and contracting motion. On receiving a shock, the whole sarcode instantly retreats within the shell. This is the description of the general type of a Globigerina animal. There are innumerable varieties, and many species have only been seen as yet in the shape of dead shells.
The red clay which seems to form the bed of all the deeper tracts is held to be composed in great part of the insoluble residue of the calcareous deposit of the "ooze," mixed with the results of the decomposition of felspathic minerals, containing much silicate of alumina and iron. The origin of the latter is still obscure. Under metamorphic conditions the " ooze" would form a chalk like that of our South Downs, and the clay would become probably a rock resembling some of the palozoic schists of the Cambrian formation.
The temperature of the ocean is invariably highest at the sur- face. Down to 100 fathoms it cools rapidly, more slowly to 500 or 600 fathoms, and with extreme slowness to the bottom, where it is almost uniform. At Fernando Neronha, almost under the Equator, it actually reaches almost to the freezing-point at the greatest depth, while at the surface its mean is 21° C., and the mean heat of the crust of the earth is not less than 8° C. The explanation of this low bottom temperature is the constant current of cold water which wells up the Atlantic at deep levels from the Antarctic Sea, interrupted only by certain accidental' barriers, while the heat of the surface is regulated by other less universal agencies. It is supposed that this constant influx from the south is neutralised by the greater evaporation in the more northerly regions, while its supply is kept up by the great deposit of rain and snow in the extreme south. The Arctic Sea, being nearly land-locked and of smaller extent, appears to have little influence. This subject is, however, yet in an immature state, and even if it were more thoroughly generalised our space forbids us to enter upon it, and upon the extensive and important question of surface currents.
We have already alluded to the fauna of the ocean in describing the " Globigerina ooze." Sir Wyville Thomson is of opinion that although no depth is absolutely destitute of animal life, the zoology of the sea exists chiefly near the surface and near the bottom, there being a large intermediate space comparatively sterile. As a rule, the larger forms exist at the surface and near the Equator. To this there are some exceptions, a large species of Holothuria, for instance (the common sea-mouse belongs to this family), being found at great depth. Many strange corals, wonderful sponges, sea-urchins, and several new crusta- ceans are described in these volumes, two of the latter being absolutely destitute of eyes, though in all their relatives the organs of sight are highly developed. Even fishes of well-marked types are found at considerable depths. Some of them, from the removal of the vast pressure to which they bad been accustomed, came up in the dredge with their eyes blown out of their heads, and their swimming-bladders forced out of their mouths and dis- tended to bursting. Tables are given showing the comparative abundance of different groups of animals at various depths, from which it will be seen that, spite of darkness and superincumbent weight of water, specimens of most of the invertebrate classes live and are duly developed at depths between 2,000 and 3,000 fathoms.
The flora of these regions is absolutely nothing at great depths, and on the surface far from land is, of course, very scanty, —limited to little more than confervoids and unicellular algte, some of these, however, occurring to vast quantities, colouringthe ocean for miles ; the only highly developed algae being the well- known Gulf-weed (Sargassum bacciferum), which spreads its floating islets over great areas.
The general reader who is not concerned with scientific details will find abundant interest in the description of various places visited in the course of the expedition, especially that of Bermudas, with its coral reefs and " Aeolian " or wind-formed rocks, of the Falkland Islands, and of Tristan d'Acunha, the most remote from the rest of the world of all human residences. One of the group- associated with the latter is inhabited during the breeding season by myriads of a large species of penguin, which lay their eggsand incubate in large communities among the tall tussock-grass, and being ignorant of man and his power and destitute of fear, inflict severe wounds with their beaks on the legs of intruders. They are supposed to have killed a poor setter belonging to the officers of the ship, who got entangled in their colony. Most of these regions have been often described before, but it is not often that we can secure that accuracy of observation and statement which the scientific character of our present travellers guarantees.
Nothing can surpass the beauty of the typography and general " get up " of these volumes, and the delicacy of the exquisite wood engravings from drawings by Mr. Wild, the extreme and conscientious accuracy of which cannot be doubted, exceeds any- thing of the kind which we have seen. The style is clear and un- pretending, and sometimes rises into picturesque description. The other more elaborate reports now in preparation will form a noble monument of the liberality of the Admiralty, and of the praiseworthy patience and industry of the scientific staff. The difficulties encountered by the latter from the great depths they had to explore, the frequent and unavoidable loss of valuable instruments, and from the necessary unsteadiness of the ship, can only be approximately realised from the details of their story.
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