The sea, as well as the air, is populous with insect life. The discoloured portions of the ocean generally owe their tint to myriads of insects. The vermilion sea off California is probably to be accounted for from this cause, "as Mr Darwin found red and chocolate-coloured water on the coast of Chili, over spaces of several square miles, full of microscopic animalcules, darting about in every direction, and sometimes exploding"—we hope for joy. "In the Arctic seas, where the water is pure transparent ultramarine colour, parts of twenty or thirty square miles, one thousand five hundred feet deep, are green and turbid, from the quantity of minute animalcules. Captain Scoresby calculated that it would require eighty thousand persons working unceasingly, from the creation of man to the present day, to count the number of insects contained in two miles of the green water."
Captain Scoresby must be very fond of calculations. We have noticed, by the way, on several occasions, how very bold these men of figures are! One pounds and pulverises the Pyrenees, and strews them over France, and tells us how many feet this would raise the level of the whole country. Another calculates how much soil the Mississippi brings down, per hour, to the ocean; and another, still bolder, undertakes to say what quantity of ice lies amongst the whole range of the Alps. Some of these calculations are laborious inutilities, as it is evident that no accurate data can be obtained to proceed upon. In the last instance, how find the depth of the ice? The sand of the desert has been sounded in one place, we are told, and the lead has sunk three hundred and sixty feet without finding a bottom; but what plummet can sound the glacier? Here and there a crevice may let us into the secret of its depth, and we know that below a certain level ice cannot remain unmelted; but who can tell the configuration of the mountain under the ice, how shallow the glacier may be in some parts, and into what profound caverns it may sink in others? There is something childish in giving us an array of figures, when the figures present no useful approximation to the truth.
We have alluded to the difficult problem of the distribution of the different species of animals throughout the several regions of the globe: the same problem meets us in the vegetable world. Here we might expect to grapple with it with some better hopes of success, yet the difficulties are by no means diminished; we only seem to see them more plainly. In the first place, it is clear, as Mrs Somerville says, that "no similarity of existing circumstances can account for whole families of plants being confined to one particular country, or even to a very limited district, which, as far as we can judge, might have grown equally well in many others." But the difference of the floras is not the only difficulty. While there is difference in a great number of the species, there is identity in a certain other number. If now we account for the difference by supposing that the several portions of land emerged from the ocean at different epochs, and under different conditions, and that, therefore, the generative powers of vegetable life, (in whatever, under the will of Divine Providence, these may be supposed to consist) manifested themselves differently, how shall we next account for this identity? "In islands far from continents, the number of plants is small; but of these a large proportion occur nowhere else. In St Helena, of thirty flower-bearing plants one or two only are native elsewhere." But these one or two become a new perplexity. "In the Falkland Islands there are more than thirty flowering plants identical with those in Great Britain." Very many similar cases might be cited; we quote these only to show the nature of the difficulty with which science has to cope.
And here comes in the following strange and startling fact, to render this subject of vegetable production still more inexplicable:—
"Nothing grows under these great forests, (of South America;) and when accidentally burnt down in the mountainous parts of Patagonia, they never rise again; but the ground they grow on is soon covered with an impenetrable brushwood of other plants. In Chili the violently stinging Loasa appears first in these burnt places, bushes grow afterwards, and then comes a tree-grass, eighteen feet high, of which the Indians make their huts. The new vegetation that follows the burning of primeval forests is quite unaccountable. The ancient and undisturbed forests of Pennsylvania have no undergrowth; and when burnt down they are succeeded by a thick growth of rhododendrons."—(Vol. ii. p. 190.)
But we must bring our rambling excursion through these pleasant volumes to a close; the more especially as we wish once more to take this opportunity, not as critics only, but as readers also, to express our grateful sense of the benefit which Mrs Somerville has conferred upon society by this and her preceding volume, The Connexion of the Physical Sciences. It was once a prevailing habit to speak in a sort of apologetic strain of works of popular science. Such habit, or whatever residue of it remains, may be entirely laid aside. If by popular science is meant the conveyance, in clear intelligible language, as little technical as possible, of the results of scientific inquiry, then are we all of us beholden more or less to popular science. The most scientific of men cannot be equally profound in all branches of inquiry. The field has now become so extensive that he cannot hope to obtain his knowledge in all departments from the first sources. He must trust for much to the authority of others. Every one who is desirous of learning what anatomy and physiology can teach us, cannot attend the dissecting table. How much that we esteem, as amongst the most valuable of our acquisitions, depends on this secondary evidence! How few can follow the calculations of the mathematician, by which he establishes results which are nevertheless familiar to all as household words! And the mathematician himself, great aristocrat as he is in science, must take the chemist on his word for the nice analysis the latter has performed. He cannot leave his papers to follow out experiments, often as difficult and intricate as his own calculations. Indeed the experiments of the man of science have become so refined and elaborate, and deal often with such subtle matter, and this in so minute quantities, that, as it has been said of the astronomer, that it requires a separate education, and takes half a life to learn to observe, so it may be truly said, that to devise and conduct new experiments in philosophy has become an art in itself. We must be content to see a great deal with the eyes of others; to be satisfied with the report of this or that labourer in the wide field of science. We cannot all of us go wandering over moor and mountain to gather and classify herbs and flowers; interested as we all are in geological speculations, we cannot all use the geological hammer, or use it to any purpose; still less can we examine all manner of fishes, or pry with the microscope into every cranny of nature for infusoria.
Mrs Somerville gives us the book!—the neat, compact, valuable volume, which we hold so commodiously in the hand. The book—the book for ever! There are who much applaud the lecture and the lecture-room, with its table full of glittering apparatus, glass and brass, and all the ingenious instruments by which nature, as we say, is put to the torture. Let such as please spend their hot uneasy hour in a crowd. We could never feed in a crowd; we detest benches and sitting in a row. To our notion, more is got, in half the time, from a few pages of the quiet letterpress, quietly perused: the better if accompanied by skilful diagrams, or, as in this case, by admirable maps. As to those experiments, on the witnessing of which so much stress is laid, it is a great fallacy to suppose that they add anything to the certainty of our knowledge. When we see an experiment performed at a distance, in a theatre, we do, in fact, as entirely rely on the word of the lecturer as if we only read of its performance. It is our faith in his character that makes all the difference between his exhibition and that of the dexterous conjurer. To obtain any additional evidence from beholding the experiment, we ought to be at the elbow of the skilful manipulator, and weigh, and test, and scrutinise.
But, indeed, as a matter of evidence, the experiment in a popular lecture-room is never viewed for a moment. It is a mere show. It has degenerated into a mere expedient to attract idlers and keep them awake. The crowd is there, and expect to see something; and it has become the confirmed habit of the whole class of popular lecturers to introduce their experiments, not when they are wanted to elucidate or prove their propositions, but whenever and wherever they can answer the purpose of amusing the audience. If a learned professor is lecturing upon the theory of combustion, he will burn a piece of stick or paper before you, to show that when such things are burnt flame is produced. He would on no account forego that flame. Yes; and the audience look on as if they had never seen a stick or a piece of paper burn before. And when he is so happy as to arrive at the point where a few grains of gunpowder may be ignited, they give him a round of applause! In the hands of many, the lecture itself becomes little more than an occasion for the experiment. The glittering vials, the air-pump, the electrical machine, undoubtedly keep the eyes at least of the audience open; but the expedient, with all due deference be it said, reminds us of the ingenious resource of the veteran exhibitor of Punch, who knows that if his puppets receive knocks enough, and there is sufficient clatter with the sticks, the dramatic dialogue may take its course as it pleases: he is sure of his popularity.
Therefore it is we are for the book; and we hold such presents as Mrs Somerville has bestowed upon the public to be of incalculable value, disseminating more sound information than all the literary and scientific institutions will accomplish in a whole cycle of their existence. We will conclude with one or two practical suggestions, which would add to the utility of the last of her two works—The Physical Geography. Mrs Somerville has thought it well to insert a few notes explanatory of some scientific terms. But these notes are few. If it was well to explain such terms as "Marsupial animals," or "Testacea," a reader might be excused for wishing to know what a "torsion balance" was, or what a "moraine,"—terms which fall upon him just as suddenly, and unexplained by any previous matter. Would not a glossary of such terms be advisable? But whatever may be thought of this suggestion, our next remark is indisputable. To such a work as this, an index is extremely useful—is all but essential. There is an index, but it is so defective, so scanty, that it is worth nothing. We cannot say whether this last remark applies equally to The Connexion of the Physical Sciences, not having that work at present under our eye. But we beg to intimate to all authors and authoresses, that whenever a book is of such a nature that it becomes valuable as a work of reference, it should be accompanied by a good index. It is a plodding business, but it must be executed.