Under various forms, such as the conservation of force, or the convertibility of one kind of energy into another, as of heat into motion, the attention of men has been more and more directed to the organic unity of Nature; and the theory of Evolution itself is but a too sweeping and hasty generalization of this conception. Nothing is more curious than to observe, throughout the history of thought, how universal is the instinct of men to seize upon some large principle, and to insist, as it were, on its dominating the whole sphere of life. It is often a characteristic of even the most powerful inductive minds to leap to some such general truth, and to establish it as a sort of major premiss, which they then apply to all their minor premisses with the unconscious instinct of purely deductive reasoners. A tendency of this kind has in great measure animated Mr. Darwin's mind throughout his career. It has, in our opinion, overpowered in some of his works the rigid caution he endeavours to practise in drawing conclusions from his observations; but it has had the immense advantage of giving him a clue for what we may call his crossexamination of Nature. It is Plato, we think, who says that if a man is to ask questions with advantage, he must previously have some surmise of the answer of which he is in search; and Mr. Darwin's surmise has evidently been, from the first, that which was suggested to him during the voyage of the 'Beagle.'

He tells us, in fact, in the Introduction to his most famous work-that on 'The Origin of Species by Means of Natural Selection' that when on board the 'Beagle' he was much struck with certain facts in the distribution of the organic beings inhabiting South America, and in the geological relations of the present to the past inhabitants of that continent. 'These facts, he says, 'seemed to throw some light on the origin of species-that mystery of mysteries, as it has been called by one of our greatest philosophers.' On his return home, it occurred to him, in 1837, 'that something might, perhaps, be made out on this question by patiently accumulating and reflecting on all sorts of facts which could possibly have any bearing on it.' After five years' work, he allowed himself to speculate on the subject, and drew up some short notes; these he enlarged in 1844 into a sketch of the conclusions which then seemed to him probable and from that period,' he adds, to the present day, I have steadily pursued the same object.' This was written in 1859; but it would remain substantially true up to the present time. Even the monograph now before us on Vegetable Mould and Earthworms has, as we shall see, its bearing on Mr. Darwin's main conception, and has been in great measure inspired by kindred ideas. The same conception

is equally conspicuous in the other works, which have from time to time borne witness to his extraordinary industry and to his fertility of thought. Not to mention his monographs on particular subjects, such as the Cirripedia,-his volumes on the Variation of Animals and Plants under Domestication'; on 'the Various Contrivances by which British and Foreign Orchids are fertilized by Insects'; on 'Insectivorous Plants'; on the Movements and Habits of Climbing Plants'; on the Effects of Cross and Self-fertilization in the Vegetable Kingdom'; on the Different Forms of Flowers in Plants of the same Species;' and on the Power of Movement in Plants;'-all combine to illustrate, among other things, two central points: the incessant and infinite interaction of the various parts of nature upon each other, and the manner in which the most conspicuous and most comprehensive results are produced by the gradual accumulation of the slightest influences. It has been justly said that any one of his books, however apparently special its subject, would give an intelligent reader a conception of the main principles which he has developed into the doctrine of Evolution. There are some of his works, besides the Origin of Species,' in which this doctrine is carried out to the full, and definitely applied to solve the problem of the origin and descent of man. These volumes, on 'The Descent of Man,' and Selection in relation to Sex,' and on the Expression of the Emotions in Man and Animals,'-while among the most interesting of his works, from the wonderful mass of minute and skilled observation which they contain,—are not, as we venture to think, those in which his judgment appears to the best advantage. They seem to us to afford some of the most conspicuous examples in our time of that method of reasoning on natural subjects which Bacon condemned under the name 'anticipatio.' His hope for the progress of science (Nov. Org.,' i. 104) depended on men being content to ascend, as it were, by a ladder, and by continuous steps, without intermissions or gaps, from particulars to the lower axioms, and from these to the middle ones, in due succession, and last of all to the most general ones'-'et postremò demum ad generalissima.' But Mr. Darwin has unfortunately in this class of his works forgotten this last caution; and, notwithstanding the admitted fact that there are numerous steps intermissi aut hiulci,' in the ladder of his observations, he has sprung at one bound to the widest generalization conceivable, and has proclaimed the discovery of the ultimate law of natural development. But his vast collection of observations, and very many of his intermediate conclusions, retain all their value and interest, and no such rich

storehouse

storehouse of facts respecting the natural history of vegetable, animal, and even human life, has perhaps ever been accumulated by a single man.

Connected, perhaps, with this continuity of thought in Mr. Darwin's writings is another characteristic not less remarkable -the continuity of the observations themselves. Each work is the result of years and tens of years of patient labour; the clue has never been dropped; and, however tortuous and obscure may be the labyrinth through which Mr. Darwin is wandering, he is at length able to trace back for us every step of the process. What is more remarkable, he will hold two or three clues in his hands at the same time, and track out simultaneously different paths through the one great labyrinth of nature. The present work on Earthworms, for instance, has been slowly growing for nearly half a century. As long ago as 1837, Mr. Darwin read a paper before the Geological Society of London on the Formation of Mould,' in which he stated the main elements of his present conclusions. It attracted but little regard at the time, being treated, for instance, by a French naturalist as no more than a 'singular theory.' But he has been patiently working at it ever since, and gradually accumulating from all quarters facts which illustrate and confirm his views. It is this which, after all, gives such unique value to his works. Sufficient honour, perhaps, is rarely done to the faculty of patient observation, nor is it realized to what an enormous extent human life and human science are built upon it. Astronomy, for instance, has now, in great measure, reached the stage of a deductive science. For a very wide range of celestial phenomena we possess the primary law, and we can announce what is, from our knowledge of what ought to be, the fact. But it is seldom remembered that this scientific knowledge reposes upon an enormous mass of observations which were accumulated through long generations of mankind. From the ancient Babylonians and Egyptians the heritage of these facts descended through tens of centuries to Greece and Rome; and fifteen centuries more of the Christian Era had to pass before they were sufficiently sifted, arranged, and tested, for a scientific conclusion to be drawn from them. Looking out upon the heavens on some starlight night, there seems something even more wonderful than the triumphs of modern astronomy in the fact that patient watching of those innumerable and apparently confused orbs should have enabled men to disentangle them, to discover a fixed order in their movements, and eventually to know them so well as to be able to predict those movements with more unerring certainty than we can feel with respect to any other occurrences. Mr.

Darwin's

Darwin's observations have not yet, as we think, placed us in a position to form a trustworthy scientific theory respecting the natural history of species, similar to the law of gravitation respecting the heavenly bodies. But he has perhaps—and that in great measure by his own herculean labours-placed us in much the same position as that to which astronomy was brought when Kepler had shown, by the laborious observations to which his genius inspired him, that the planets moved in ellipses. We now know, as it were, in what orbits species have moved, and we know, within certain limits, the methods of their variation. To this extent it may be said that we know the fact of evolution. But what are its causes, what is the law which impels the variation of species in known directionswhether it is by an inherent principle of development, like that which determines the growth of an individual, or by the pressure of external circumstances, or by both combined, that the observed results are produced-this, as it seems to us, is as unknown as was the law of gravitation before Newton divined it. But it is Mr. Darwin's achievement to have finally established the facts, and also to have shown that a vast number of them can be accounted for by natural causes now in operation. There remain many, especially in relation to man, which have not thus been explained, and it is rash and unscientific to assume, without direct evidence, that they can be so. This, as we think, is Mr. Darwin's error. His strength is exhibited in the wonderful grasp with which he has brought all the facts in question together, with which he has arranged and organized them, and has revealed to us, with a clearness which had never before been approached, if not the causes which determine the order of natural history, at least that order itself. What he has done, to recur to the illustration first offered, may be said to be, that he has abolished the kind of Ptolemaic theory of natural history which previously prevailed, and has established a Copernican theory, substituting for an ingenious artificial account of the order of nature one which corresponds to the actual facts. But it is another thing to make the further step which was made by Newton, in the discovery of a universal law, and it is this which, as we believe, has not yet been done.

But to turn to the particular volume before us, the reader will find in it a condensed display of all these characteristic qualities. Perhaps, indeed, part of its excellence is due to a legitimate exercise of the very quality, which in another respect Mr. Darwin seems to us to have unduly indulged. Notwithstanding what we have said above in depreciation of the menta} habit which Bacon stigmatized as anticipation,' it must

be

It

A

be admitted that Mr. Darwin has abundantly justified the employment, in its due place, of what Professor Tyndall has described as the function of the Imagination in Science. more conspicuous exercise of the scientific imagination than that which gave rise to this book cannot easily be conceived. appears from it that at the very commencement of his scientific career, fifty years ago, some casual observations suggested to Mr. Darwin the idea, that worms were possibly among the most considerable forces in nature, and that they had played a very large part in the natural history of the world. To how few persons could such a conception have occurred! It would be one thing if, as the result of years of laborious enquiry, the conviction had been slowly forced on a naturalist, that worms had played this part in nature. But it is another thing, that Mr. Darwin divined it from a few facts and proceeded to work out the evidence for it. He acknowledges, indeed, with his usual justice, that he received the first suggestion of the idea from Mr. Wedgwood, of Maer Hall, in Staffordshire. But Mr. Wedgwood seems to have applied it only to the explanation of the sinking beneath the earth of bodies lying on its surface, while Mr. Darwin appears at once to have sprung to the imagination that all the vegetable mould over the whole country has passed many times through, and will again pass many times through, the intestinal canals of worms,' so that the term 'animal mould' would be in some respects more appropriate than that of vegetable mould.' Mr. Darwin must have been already deeply imbued with the cardinal idea of his subsequent investigations, to have entertained such a conception. Not merely to unscientific, but to scientific men, the earthworm had hitherto appeared one of the most insignificant of all creatures. As we have already noticed, distinguished French naturalists almost scorned Mr. Darwin's suggestion when it was first propounded. Even as late as 1869, Mr. Darwin tells us, Mr. Fish, in the Gardeners' Chronicle,' rejected his conclusions with respect to the part which worms have played in the formation of vegetable mould, merely on account of their assumed incapacity to do so much work. Considering,' said Mr. Fish, their weakness and their size, the work they are represented to have accomplished is stupendous.' Mr. Darwin's observation on this objection is characteristic and instructive, and indicates the connection of his study of this subject with the main work of his life. Here,' he says, 'we have an instance of that inability to sum up the effects of a continually recurrent cause, which has often retarded the progress of science, as formerly in the case of geology, and more recently in that of the

principle