Читать книгу Life of Charles Darwin - Bettany George Thomas - Страница 4

ON his return home, Darwin speedily placed himself in communication with the leaders of scientific progress, and, in consequence of the valuable results of his voyage, he soon found himself in a most advantageous position. On November 20, 1836, he was elected a Fellow of the Geological Society, and before the end of the year he had sent the manuscript of one of his early papers to Lyell, who writes to him (December 26, 1836): “I have read your paper with the greatest pleasure… What a splendid field you have to write upon.” He strongly advised the young man not to accept any official scientific place, but to devote himself to his own line of work. But Darwin was overpersuaded, and became a member of the Council of the Geological Society in the following February, and secretary in February, 1838. This office he held with success for three years. Lyell referred in considerable detail to the young traveller’s views in his presidential address to the Society in 1837.

Darwin’s geological papers soon became numerous. In 1837 he discussed in succession the recent elevation of the coast of Chili, the deposits containing extinct mammalia in the neighbourhood of the Plata, the areas of elevation and subsidence in the Pacific and Indian Oceans, as deduced from the study of coral formations, and the formation of mould (the precursor of a work he issued more than forty years later). Papers on the connection of certain volcanic phenomena, and on the formation of mountain chains, and other geological notes on South America, were read in 1838; the interesting Parallel Roads of Glen Roy, in Scotland, which he believed to be of marine origin, were described in 1839; the erratic (glacial) boulders of South America, in 1841; and coral reefs in 1842: a full record, one would imagine, of busy years, occupied also with secretarial work. Lyell, writing to Sir John Herschel (May 24, 1837), says: “I am very full of Darwin’s new theory of coral islands, and have urged Whewell to make him read it at our next meeting. I must give up my volcanic crater theory for ever, though it costs me a pang at first.” In March, 1838, Lyell describes the reception of the paper on volcanic phenomena at the Geological Society. “He opened upon De la Beche, Phillips, and others, his whole battery of the earthquakes and volcanoes of the Andes; and argued that spaces of a thousand miles long were simultaneously subject to earthquakes and volcanic eruptions, and that the elevation of the Pampas, Patagonia, &c., all depended upon a common cause.” In fit acknowledgment of such services to science, he was elected a Fellow of the Royal Society on January 24, 1839.

Early in 1839 Darwin married his cousin, Emma Wedgwood, daughter of his uncle Josiah Wedgwood: a union which, though consanguineous, proved in the highest degree congenial and fortunate. In succeeding years a numerous family of sons and daughters surrounded the happy parents. After considerable delays by the Admiralty, though it had long been ready, the Journal appeared, in 1839, as the third volume of Fitzroy’s “Voyages of The Adventure and Beagle.” The Quarterly Review (lxv. 224) said that there could be no two opinions of its merits. “We find ample materials for deep thinking; we have the vivid description that fills the mind’s eye with brighter pictures than painter can present, and the charm arising from the freshness of heart which is thrown over these virgin pages of a strong intellectual man, and an acute and deep observer.” Its merits, however, were somewhat slow to become known to the general public, owing to the original expensive form of publication; and it was not till 1845, when the second and enlarged edition appeared as “The Journal of Researches,” that the popular ear was gained. Later, under the title, “A Naturalist’s Voyage Round the World,” the book has become very widely known and appreciated.

The publication of “The Zoology of the Voyage of The Beagle,” commenced in 1838, under Darwin’s superintendence, gave a fuller view of the acquisitions to natural history which had been made than had previously been possible. The Treasury, acting on the representations of the presidents of the Linnean, Zoological, and Geological Societies, as well as of the naturalist himself, in 1837 made a grant of £1000 towards the expenses of publication of these memoirs. Owen’s description of the fossil mammalia, completed in 1840; G. Waterhouse’s of the living mammalia, in 1839; Gould’s of the birds, in 1841; L. Jenyns’s of the fish, in 1842; and Thomas Bell’s of the reptiles, in 1843 – all in quarto, with beautiful plates, were a solid testimony to a splendid success. Darwin furnished an introduction to each part, and the portions of the text referring to the habits and ranges of the living animals. Three species of mastodon and the gigantic megatherium were the only extinct mammalia known from South America previous to Darwin’s voyage. To these were now added the Mylodon Darwinii, a giant sloth; the scelidotherium, a somewhat smaller form; the great camel-like, yet odd-toed, macrauchenia; and the toxodon, as large as a hippopotamus, yet having a strange resemblance to the little rodents. All these belonged to geological deposits not far anterior to the present age. The collections of living vertebrates were less profoundly interesting, but the number of new species was large; and the habits and localities being recorded by so good an observer, gave them additional value.

The fossil mammals were given by the generous traveller to the London College of Surgeons, the mammals and birds to the Zoological Society, the reptiles to the British Museum, and the fishes to the Cambridge Philosophical Society. Nor was this all. The collections of insects, shells, and crustacea were described by many able specialists in scientific publications. The flowering plants were described by Hooker, and the non-flowering by Berkeley; and, altogether, no expedition ever yielded a more solid result to the scientific naturalist, while furnishing a delightful narrative to the general reader, and laying the foundation for generalisations of surpassing importance to all thinking minds.

It was evident to many geologists that the greatest value would attach to the full record of the geological observations made by the gifted young secretary of the Geological Society. A year after the publication of the Journal the first portion of these observations, dealing with coral reefs, was almost ready, but the continued ill-health of the author delayed the publication till 1842. When it appeared, under the title of “The Structure and Distribution of Coral Reefs,” its success was immediate and complete.

Ever since their first description by voyagers, marvel had been expressed at the strange and beautiful phenomena presented by coral islands. Coral, as being built up by the tireless labours of innumerable so-called “insects,” or “worms,” had become associated with romantic ideas. It really consists of the internal skeletons of coral-polyps, allied to the sea anemone. Captain Basil Hall, in his “Voyage to Loo Choo,” looking with the eyes of one ignorant of zoology, had credited the building of coral reefs to all kinds of creatures which lived on and near the coral after it had been made; and his erroneous views had been amplified and developed by James Montgomery, in his “Pelican Island,” into the most fantastically incorrect description that ever versifier penned. Sad to relate, his lines were often quoted, as if correct, by scientific men in pre-Darwinian times.

Nothing gives clearer evidence of the power of mind which Darwin had already attained when voyaging round the world than the originality of his views on coral reefs. The lagoon islands, or atolls, he describes as “vast rings of coral rock, often many leagues in diameter, here and there surmounted by a low verdant island, with dazzling white shores, bathed on the outside by the foaming breakers of the ocean; and, on the inside, surrounding a calm expanse of water which, from reflection, is of a bright, but pale, green colour.” Keeling atoll, outside which, at less than a mile and a half distance, no bottom was found with a line 7,200 feet in length, having been fully described, and an account given of all other known atoll systems, the peculiarities of the great barrier reef of North-east Australia, and that of New Caledonia, were recounted. Off the latter, no bottom was found, at two ships’ length from the reef, with a line 900 feet long. With these were linked the smaller reefs of Tahiti and others, where considerable islands are more or less completely surrounded by them. Next, the fringing or shore reefs, at first sight only a variety of barrier reefs, were clearly distinguished from them by the absence of an interior deep-water channel, and their not growing up from an immense, but from a moderate depth of water.

The remarkable fact was pointed out by Darwin that all coral islands are within a little more than 30 degrees of the Equator, but that, at the same time, they are absent over certain larger areas within the tropical seas. There are none on the West Coast of South America, nor on the West Coast of Africa. In this portion of his work we have another significant sentence bearing on the struggle for existence. In discussing the apparently capricious distribution of coral reefs, he remarks that “the study of the terrestrial and better-known half of the world must convince every one that no station capable of supporting life is lost – nay more, that there is a struggle for each station between the different orders of nature.” He describes the large fishes and the trepangs (holothuriæ) preying upon the coral-polyps, and shows how complex are the conditions which determine the formation of reefs on any shore. Perhaps no part of his work is more important than that in which he collects the evidence proving how rapidly coral masses grow, and that they for the most part cannot flourish in a greater depth of water than fifteen fathoms.

Reasoning upon the facts observed by himself and others Darwin now proceeded to upset the received theory that atolls were based upon submarine volcanic craters, and to substitute for it the view that there has been a prolonged and gradual subsidence of the areas upon which the atolls are based, and a corresponding upward growth of the reef-building corals. Thus fringing-reefs in time become barrier-reefs; and barrier-reefs, when they encircle islands, are converted into atolls, or lagoon islands, as soon as the last pinnacle of land sinks beneath the surface of the ocean. The whole matter is summed up thus: “A magnificent and harmonious picture of the movements which the crust of the earth has within a late period undergone is presented to us. We see vast areas rising, with volcanic matter every now and then bursting forth through the vents or fissures with which they are traversed. We see other wide spaces slowly sinking without any volcanic outbursts; and we may feel sure that this sinking must have been immense in amount as well as in area, thus to have buried over the broad face of the ocean every one of these mountains above which atolls now stand like monuments, marking the place of their former existence.” “No more admirable example of scientific method was ever given to the world,” says Professor A. Geikie, “and even if he had written nothing else, this treatise alone would have placed Darwin in the very front of investigators of nature.”

After thirty-two years’ interval, a second edition of “Coral Reefs” appeared, in a cheaper form, in 1874. It is rare indeed for a scientific treatise to attain at once and maintain so long a position of such undisputed authority. The eminent German naturalist, Semper, in 1863, criticised the general theory in consequence of his own careful examination of the Pelew Islands; but Darwin easily answered him by pointing to the cumulative evidence in favour of his own views. The only really important work on the subject, after Darwin’s, was that of Professor J. D. Dana, the eminent American naturalist and geologist, on “Corals and Coral Islands,” published in 1872. Darwin, in the preface to his second edition, candidly acknowledged that he had not previously laid sufficient weight on the mean temperature of the sea in determining the distribution of coral reefs; but this did not touch his main conception. In fact, he maintained his ground undisturbed, and at the same time admired greatly Dana’s book, which was the result of personal examination of more coral formations than perhaps any one man had ever studied, and which accepted Darwin’s fundamental proposition, that lagoon islands or atolls and barrier-reefs have been formed during periods of subsidence.5

No such strikingly original theory is propounded in the second part of “The Geology of the Beagle” dealing chiefly with volcanic islands. St. Jago, in the Cape de Verde Islands; Fernando Noronha, Terceira, Tahiti, Mauritius, St. Paul’s, Ascension, St. Helena, and the Galapagos are in turn more or less fully described, according to the opportunities the explorer had possessed. To some extent, as in the succeeding part, Darwin adapts his views on mountain elevation too closely to those enunciated by Elie de Beaumont. The third part of the geology of the Beagle, entitled “Geological Observations on South America,” was not published till 1846. Even this did not exhaust the contributions to geology made from the Beagle voyage, for it did not include the papers on the “Connection of certain Volcanic Phenomena in South America” (1838); on the “Distribution of Erratic Boulders” (1841); on the “Fine Dust which falls on Vessels” (1845); and on the “Geology of the Falkland Islands” (1846). A second edition of the two latter parts of “The Geology of the Beagle” was published in one volume in 1876.

Meanwhile, after spending a few years of his early married life in London, during which he was often in ill-health, Darwin fixed his residence in 1842 at Down House, near Beckenham, Kent. The little village of Down, three or four miles from the Orpington railway station, was near enough to London for convenient access, yet greatly secluded and thoroughly rural. The traveller’s roving days were over, and his infirmity of health prevented him from undertaking very fatiguing journeys. After the cessation of his active work for the Geological Society, Darwin’s chief public appearance was when he spoke at the Oxford meeting of the British Association, in 1847, when, strange to say, Ruskin was secretary of the Geological Section.

At Down then, situated some 400 feet above the sea level on a plateau of chalk, interrupted by wavy hollows with beech woods on the slopes, about forty years of Darwin’s life were passed. Down House, one of the square red brick mansions of the last century, to which have been since added a gable-fronted wing on one side and a more squarely-built wing and pillared portico on the other, is shut in and almost hidden from the roadway by a high wall and belt of trees. On the south side a walled garden opens into a quiet meadow, bounded by underwood, through which is seen a delightful view of the narrow valley beyond, towards Westerham.

One of the most admirable chapters of the well-known “Manual of Scientific Enquiry,” published in 1849, for the use of the navy and travellers generally, and edited by Sir John Herschel, was Darwin’s, on Geology. The explorer is here taught to make the most of his opportunities upon the soundest principles. The habits which the author had himself formed are inculcated upon the observer – copious collecting, accurate recording, much thinking. Nothing is omitted. Number-labels which can be read upside down must have a stop to indicate the right way up; every specimen should be ticketed on the day of collection; diagrams of all kinds should be made, as nearly as possible, to scale. “Acquire the habit of always seeking an explanation of every geological point met with.” “No one can expect to solve the many difficulties which will be encountered, and which for a long time will remain to perplex geologists; but a ray of light will occasionally be his reward, and the reward is ample.” Truly an ample reward awaited the observer who could thus speak of the value of “a ray of light;” he certainly did, to use the concluding words of the essay, “enjoy the high satisfaction of contributing to the perfection of the history of this wonderful world.”

Meanwhile Darwin had been carrying on a great research on the very peculiar order of crustacea, termed Cirripedia, better known as barnacles and acorn shells. He had originally only intended to describe a single abnormal member of the group, from South America, but was led, for the sake of comparison, to examine the internal parts of as many as possible. The British Museum collection was freely opened to him, and as the importance of studying the anatomy of many specimens became evident, the splendid collections of Messrs. Stutchbury, Cuming, and others were placed at his disposal, and he was permitted to open and to dissect unique specimens of great value. In fact, almost every naturalist of note who had any knowledge of the subject freely aided him, and the result was a masterly series of finely illustrated volumes; two on the living Cirripedia, issued by the Ray Society in 1851 and 1854; and two on the fossil Cirripedia of Great Britain, by the Palæontographical Society, published in the same years. There is evidence in these volumes that careful observations on the growth of these creatures had been made as far back as the visit to the Galapagos Islands in 1835. In many respects these works are as masterly as any the author ever wrote. Considering the previous obscurity of the subject, the difficulties attending the research, the almost entire lack at that time of any general microscopical knowledge of tissues, and especially of those of embryos, Darwin’s success is marvellous. The details are too technical for statement here, but any one with a zoological training, who studies the strange complication of the reproductive systems, and the remarkable transformations which the young undergo, as told in these volumes, will appreciate more than ever the breadth and the solidity of the basis of patiently acquired knowledge which Charles Darwin had accumulated while his “Origin of Species” was taking shape.