Science is mind applied to nature. The external world only exists for us so far as we conceive it within ourselves, and as it shapes itself within us into the form of a contemplation of nature. As intelligence and language, thought and the signs of thought, are united by secret and indissoluble links, so, and almost without our being conscious of it, the external world and our ideas and feelings melt into each other.

"External phenomena are translated," as Hegel expresses it in his "Philosophy of History," "in our internal representation of them." The objective world, thought by us, reflected in us, is subjected to the unchanging, necessary, and all-conditioning forms of our intellectual being.

The activity of the mind exerts itself on the elements furnished to it by the perceptions of the senses. Thus, in the youth of nations there manifests itself in the simplest intuition of natural facts, in the first efforts made to comprehend them, the germ of the philosophy of nature.

If the study of physical phenomena be regarded in its bearings not on the material wants of man, but on his general intellectual progress, its highest result is found in the knowledge of those mutual relations which link together the general forces of nature. It is the intuitive and intimate persuasion of the existence of these relations which at once enlarges and elevates our views and enhances our enjoyment. Such extended views are the growth of observation, of meditation, and of the spirit of the age, which is ever reflected in the operations of the human mind whatever may be their direction.

From the time when man, in interrogating nature, began to experiment or to produce phenomena under definite conditions, and to collect and record the fruits of his experience--so that investigation might no longer be restricted by the short limits of a single life--the philosophy of nature laid aside the vague and poetic forms with which she had at first been clothed, and has adopted a more severe character.

The history of science teaches us how inexact and incomplete observations have led, through false inductions, to that great number of erroneous physical views which have been perpetuated as popular prejudices among all cla.s.ses of society. Thus, side by side with a solid and scientific knowledge of phenomena, there has been preserved a system of pretended results of observation, the more difficult to shake because it takes no account of any of the facts by which it is overturned.

This empiricism--melancholy inheritance of earlier times--invariably maintains whatever axioms it has laid down; it is arrogant, as is everything that is narrow-minded; while true physical philosophy, founded on science, doubts because it seeks to investigate thoroughly--distinguishes between that which is certain and that which is simply probable--and labours incessantly to bring its theories nearer to perfection by extending the circle of observation. This a.s.semblage of incomplete dogmas bequeathed from one century to another, this system of physics made up of popular prejudices, is not only injurious because it perpetuates error with all the obstinacy of ill-observed facts, but also because it hinders the understanding from rising to the level of great views of nature.

Instead of seeking to discover the _mean_ state around which, in the midst of apparent independence and irregularity, the phenomena really and invariably oscillate, this false science delights in multiplying apparent exceptions to the dominion of fixed laws, and seeks, in organic forms and the phenomena of nature, other marvels than those presented by internal progressive development, and by regular order and succession.

Ever disinclined to recognise in the present the a.n.a.logy of the past, it is always disposed to believe the order of nature suspended by perturbations, of which it places the seat, as if by chance, sometimes in the interior of the earth, sometimes in the remote regions of s.p.a.ce.

_II.--The Inductive Method_

The generalisation of laws which were first applied to smaller groups of phenomena advances by successive gradations, and their empire is extended, and their evidence strengthened, so long as the reasoning process is directed to really a.n.a.logous phenomena. Empirical investigation begins by single perceptions, which are afterwards cla.s.sed according to their a.n.a.logy or dissimilarity. Observation is succeeded at a much later epoch by experiment, in which phenomena are made to arise under conditions previously determined on by the experimentalist, guided by preliminary hypotheses, or a more or less just intuition of the connection of natural objects and forces.

The results obtained by observation and experiment lead by the path of induction and a.n.a.logy to the discovery of empirical laws, and these successive phases in the application of human intellect have marked different epochs in the life of nations. It has been by adhering closely to this inductive path that the great ma.s.s of facts has been acc.u.mulated which now forms the solid foundation of the natural sciences.

Two forms of abstraction govern the whole of this cla.s.s of knowledge--_viz._, the determination of quant.i.tative relations, according to number and magnitude; and relations of quality, embracing the specific properties of heterogeneous matter.

The first of these forms, more accessible to the exercise of thought, belongs to the domain of mathematics; the other, more difficult to seize, and apparently more mysterious, to that of chemistry. In order to submit phenomena to calculation, recourse is had to a hypothetical construction of matter by a combination of molecules and atoms whose number, form, position, and polarity determine, modify, and vary the phenomena.

We are yet very far from the time when a reasonable hope could be entertained of reducing all that is perceived by our senses to the unity of a single principle; but the partial solution of the problem--the tendency towards a general comprehension of the phenomena of the universe--does not the less continue to be the high and enduring aim of all natural investigation.

_III.--Distribution of Matter in s.p.a.ce_

A physical cosmography, or picture of the universe, should begin, not with the earth, but with the regions of s.p.a.ce--the distribution of matter in the universe.

We see matter existing in s.p.a.ce partly in the form of rotating and revolving spheroids, differing greatly in density and magnitude, and partly in the form of self-luminous vapour dispersed in shining nebulous spots or patches. The nebulae present themselves to the eye in the form of round, or nebulous discs, of small apparent magnitude, either single or in pairs, which are sometimes connected by a thread of light; when their diameters are greater their forms vary--some are elongated, others have several branches, some are fan-shaped, some annular, the ring being well defined and the interior dark. They are supposed to be undergoing various and progressive changes of form, as condensation proceeds around one or more nuclei in conformity with the laws of gravitation. Between two and three thousand of such unresolvable nebulae have already been counted, and their positions determined.

If we leave the consideration of the attenuated vaporous matter of the immeasurable regions of s.p.a.ce, whether existing in a dispersed state as a cosmical ether without form or limits, or in the shape of nebulae, and pa.s.s to those portions of the universe which are condensed into solid spheres or spheroids, we approach a cla.s.s of phenomena exclusively designated as stars or as the sidereal universe. Here, too, we find different degrees of solidity or density in the agglomerated matter.

If we compare the regions of s.p.a.ce to one of the island-studded seas of our planet, we may imagine we see matter distributed in groups, whether of unresolvable nebulae of different ages condensed around one or more nuclei, or in cl.u.s.ters of stars, or in stars scattered singly. Our cl.u.s.ter of stars, or the island in s.p.a.ce to which we belong, forms a lens-shaped, flattened, and everywhere detached stratum, whose major axis is estimated at seven or eight hundred, and its minor axis at a hundred and fifty times, the distance of Sirius. If we a.s.sume that the parallax of Sirius does not exceed that accurately determined for the brightest stars in Centaur (0.9128 sec.), it will follow that light traverses one distance of Sirius in three years, while nine years and a quarter are required for the transmission of the light of the star 61 Cygni, whose considerable proper motion might lead to the inference of great proximity.

Our cl.u.s.ter of stars is a disc of comparatively small thickness divided, at about a third its length, into two branches; we are supposed to be near this division, and nearer to the region of Sirius than to that of the constellation of the Eagle; almost in the middle of the starry stratum in the direction of its thickness.

The place of our solar system and the form of the whole lens are inferred from a kind of scale--_i.e._, from the different number of stars seen in equal telescopic fields of view. The greater or less number of stars measures the relative depth of the stratum in different directions; giving in each case, like the marks on a sounding-line, the comparative length of visual ray required to reach the bottom; or, more properly, as above and below do not here apply, the outer limit of the sidereal stratum.

In the direction of the major axis, where the greater number of stars are placed behind each other, the remoter ones appear closely crowded together, and, as it were, united by a milky radiance, and present a zone or belt projected on the visible celestial vault. This narrow belt is divided into branches; and its beautiful, but not uniform brightness, is interrupted by some dark places. As seen by us on the apparent concave celestial sphere, it deviates only a few degrees from a great circle, we being near the middle of the entire starry cl.u.s.ter, and almost in the plane of the Milky Way. If out planetary system were far outside the cl.u.s.ter, the Milky Way would appear to telescopic vision as a ring, and at a still greater distance as a resolvable disc-shaped nebula.

_IV.--On Earth History_

The succession and relative age of different geological formations are traced partly by the order of superposition of sedimentary strata, of metamorphic beds, and of conglomerates, but most securely by the presence of organic remains and their diversities of structure. In the fossiliferous strata are inhumed the remains of the floras and faunas of past ages. As we descend from stratum to stratum to study the relations of superposition, we ascend in the order of time, and new worlds of animal and vegetable existence present themselves to the view.

In our ignorance of the laws under which new organic forms appear from time to time upon the surface of the globe, we employ the expression "new creations" when we desire to refer to the historical phenomena of the variations which have taken place at intervals in the animals and plants that have inhabited the basins of the primitive seas and the uplifted continents.

It has sometimes happened that extinct species have been preserved entire, even to the minutest details of their tissues and articulations.

In the lower beds of the Secondary Period, the lias of Lyme Regis, a sepia has been found so wonderfully preserved that a part of the black fluid with which the animal was provided myriads of years ago to conceal itself from its enemies has actually served at the present time to draw its picture. In other cases such traces alone remain as the impression which the feet of animals have left on wet sand or mud over which they pa.s.sed when alive, or the remains of their undigested food (coprolites).

The a.n.a.lytical study of the animal and vegetable kingdoms of the primitive world has given rise to two distinct branches of science; one purely morphological, which occupies itself in natural and physiological descriptions, and in the endeavour to fill up from extinct forms the chasms which present themselves in the series of existing species; the other branch, more especially geological considers the relations of the fossil remains to the superposition and relative age of the sedimentary beds in which they are found. The first long predominated; and the superficial manner which then prevailed of comparing fossil and existing species led to errors of which traces still remain in the strange denominations which were given to certain natural objects. Writers attempted to identify all extinct forms with living species, as, in the sixteenth century, the animals of the New World were confounded by false a.n.a.logies with those of the Old.

In studying the relative age of fossils by the order of superposition of the strata in which they are found, important relations have been discovered between families and species (the latter always few in numbers) which have disappeared and those which are still living. All observations concur in showing that the fossil floras and faunas differ from the present animal and vegetable forms the more widely in proportion as the sedimentary beds to which they belong are lower, or more ancient.

Thus great variations have successively taken place in the general types of organic life, and these grand phenomena, which were first pointed out by Cuvier, offer numerical relations which Deshayes and Lyell have made the object of researches by which they have been conducted to important results, especially as regards the numerous and well-preserved fossils of the Tertiary formation. Aga.s.siz, who has examined 1,700 species of fossil fishes, and who estimates at 8,000 the number of living species which have been described, or which are preserved in our collections, affirms that, with the exception of one small fossil fish peculiar to the argillaceous geodes of Greenland, he has never met in the Transition, Secondary, or Tertiary strata with any example of this cla.s.s specifically identical with any living fish; and he adds the important remark that even in the lower Tertiary formations a third of the fossil fishes of the _calcaire grossier_ and of the London clay belong to extinct families.

We have seen that fishes, which are the oldest vertebrates, first appear in the Silurian strata, and are found in all the succeeding formations up to the birds of the Tertiary Period. Reptiles begin in like manner in the magnesian limestone, and if we now add that the first mammalia are met with in Oolite, the Stonefield slate; and that the first remains of birds have been found in the deposits of the cretaceous period, we shall have indicated the inferior limits, according to our present knowledge, of the four great divisions of the vertebrates.

In regard to invertebrate animals, we find corals and some sh.e.l.ls a.s.sociated in the oldest formations with very highly organised cephalopodes and crustaceans, so that widely different orders of this part of the animal kingdom appear intermingled; there are, nevertheless, many isolated groups belonging to the same order in which determinate laws are discoverable. Whole mountains are sometimes found to consist of a single species of fossil goniat.i.tes, trilobites, or nummulites.

Where different genera are intermingled, there often exists a systematic relation between the series of organic forms and the superposition of the formations; and it has been remarked that the a.s.sociation of certain families and species follows a regular law in the superimposed strata of which the whole const.i.tutes one formation. It has been found that the waters in the most distant parts of the globe were inhabited at the same epochs by testaceous animals corresponding, at least in generic character, with European fossils.

Strata defined by their fossil contents, or by the fragments of other rocks which they include, form a geological horizon by which the geologist may recognise his position, and obtain safe conclusions in regard to the ident.i.ty or relative antiquity of formations, the periodical repet.i.tion of certain strata--their parallelism--or their entire suppression. If we would thus comprehend in its greatest simplicity the general type of the sedentary formations, we find in proceeding successively from below upwards: (1) The Transition group, including the Silurian and Devonian (Old Red Sandstone) systems; (2) the Lower Trias, comprising mountain limestone, the coal measures, the lower new red sandstone, and the magnesian limestone; (3) the Upper Trias, composing the bunter, or variegated sandstone, the muschelkalk, and the Keuper sandstone; (4) the Oolitic, or Jura.s.sic series, including Lias; (5) the Cretaceous series; (6) the Tertiary group, as represented in its three stages by the _calcaire grossier_ and other beds of the Paris basin, the lignites, or brown coal of Germany, and the sub-Apennine group of Italy.

To these succeed transported soils (_alluvium_), containing the gigantic bones of ancient mammalia, such as the mastodons, the dinotherium, and the megatheroid animals, among which is the mylodon of Owen, an animal upwards of eleven feet in length, allied to the sloth. a.s.sociated with these extinct species are found the fossil remains of animals still living: elephants, rhinoceroses, oxen, horses, and deer. Near Bogota, at an elevation of 8,200 French feet above the level of the sea, there is a field filled with the bones of mastodon (_Campo de Gigantes_), in which I have had careful excavations made. The bones found on the table-lands of Mexico belong to the true elephants of extinct species. The minor range of the Himalaya, the Sewalik hills, contain, besides numerous mastodons, the sivatherium and the gigantic land-tortoise (_Colossochelys_), more than twelve feet in length and six in height, as well as remains belonging to still existing species of elephants, rhinoceroses, and giraffes. It is worthy of notice that these fossils are found in a zone which enjoys the tropical climate supposed to have prevailed at the period of the mastodons.

_V.--The Permanence of Science_

It has sometimes been regarded as a discouraging consideration that, while works of literature being fast-rooted in the depths of human feeling, imagination and reason suffer little from the lapse of time, it is otherwise with works which treat of subjects dependent on the progress of experimental knowledge. The improvement of instruments, and the continued enlargement of the field of observation, render investigations into natural phenomena and physical laws liable to become antiquated, to lose their interest, and to cease to be read.

Let none who are deeply penetrated with a true and genuine love of nature, and with a lively appreciation of the true charm and dignity of the study of her laws, ever view with discouragement or regret that which is connected with the enlargement of the boundaries of our knowledge. Many and important portions of this knowledge, both as regards the phenomena of the celestial s.p.a.ces and those belonging to our own planet, are already based on foundations too firm to be lightly shaken; although in other portions general laws will doubtless take the place of those which are more limited in their application, new forces will be discovered, and substances considered as simple will be decomposed, while others will become known.

JAMES HUTTON

The Theory of the Earth

James Hutton, the notable Scotch geologist, was born at Edinburgh on June 3, 1726. In 1743 he was apprenticed to a Writer to the Signet; but his apprenticeship was of short duration and in the following year he began to study medicine at Edinburgh University, and in 1749 graduated as an M.D. Later he determined to study agriculture, and went, in 1752, to live with a Norfolk farmer to learn practical farming. He did not devote himself entirely to agriculture, but gave a considerable amount of his time to chemical and geological researches. His geological researches culminated in his great work, "The Theory of the Earth," published at Edinburgh in 1795. In this work he propounds the theory that the present continents have been formed at the bottom of the sea by the precipitation of the detritus of former continents, and that the precipitate had been hardened by heat and elevated above the sea by the expansive power of heat. He died on March 26, 1797. Other works are his "Theory of Rain," "Elements of Agriculture," "Natural Philosophy," and "Nature of Coal."

_I.--Origin and Consolidation of the Land_

The solid surface of the earth is mainly composed of gravel, of calcareous, and argillaceous strata. Sand is separated by streams and currents, gravel is formed by the attrition of stones agitated in water, and argillaceous strata are deposited by water containing argillaceous material. Accordingly, the solid earth would seem to have been mainly produced by water, wind, and tides, and this theory is confirmed by the discovery that all the ma.s.ses of marble and limestone are composed of the calcareous matter of marine bodies. All these materials were, in the first place, deposited at the bottom of the sea, and we have to consider, firstly, how they were consolidated; and secondly, how they came to be dry land, elevated above the sea.

It is plain that consolidation may have been effected either through the concretion of substances dissolved in water or through fusion by fire. Consolidation through the concretion of substances dissolved in the sea is unlikely, for, in the first place, there are strata, such as siliceous matter, which are insoluble, and which could not therefore have been in solution; and, in the second place, the appearance of the strata is contrary to this supposition. Consolidation was probably effected by heat and fusion. All the substances in the earth may be rendered fluid by heat, and all the appearances in the earth's crust are consistent with the consolidation and crystallisation of fused substances. Not only so, but we find rents and separations and veins in the strata, such as would naturally occur in strata consolidated by the cooling of fused ma.s.ses, and other phenomena pointing to fusion by heat.

We may conclude, then, that all the solid strata of the globe have been hardened from a state of fusion.

But how were these strata raised up from the bottom of the sea and transformed into dry land? Even as heat was the consolidating power, so heat was also probably the elevating power. The power of heat for the expansion of bodies is, as we know, unlimited, and the expansive power of heat was certainly competent to raise the strata above the sea. Heat was certainly competent, and if we examine the crust of the earth we find evidence that heat was used.

If the strata cemented by the heat of fusion were created by the expansive power of heat acting from below, we should expect to find every species of fracture, dislocation, and contortion in those bodies, and every degree of departure from a horizontal towards a vertical position. And this is just what we do find. From horizontal, the strata are frequently found vertical; from continuous, broken, and separated in every possible direction; and from a plane, bent and doubled. The theory is confirmed by an examination of the veins and fissures of the earth which contain matter foreign to the strata they traverse, and evidently forced into them as a fluid under great pressure. Active volcanoes, and extinct volcanoes, and the marks everywhere of volcanic action likewise support the theory of expansion and elevation by heat. A volcano is not made on purpose to frighten superst.i.tious people into fits of piety and devotion; it is to be considered as a spiracle of a subterranean furnace.