sible to mathematical treatment, has been the means of increasing in the most marvellous manner the splendour of the higher forms of analysis, and has equally enlarged the limits of the extensive domain of optics; our earthly sphere, on the other hand, by its heterogeneity of elements, and by the complicated play of the expressions of force inherent in matter, has formed a basis for chemistry, and for all those branches of physical science which treat of phenomena, that have not as yet been found to be connected with vibrations generating heat and light. Each sphere has, therefore, in accordance with the nature of the problems which it presents to our investigation, exerted a different influence on the intellectual activity and scientific knowledge of mankind.

All celestial bodies, excepting our own planet and the aerolites which are attracted by it, are, to our conception composed only of homogeneous gravitating matter, without any specific or so-called elementary difference of substances. Such a simple assumption is, however, not by any means based upon the inner nature and constitution of these remote celestial orbs, but arises merely from the simplicity of the hypotheses, which are capable of explaining and leading us to predict the movements of the heavenly bodies. This idea arises, as I have already had occasion frequently to remark (Cosmos, vol. i, pp. 44-49 and pp. 124-125; vol. iii, pp. 2, 18, and 22-28), from the exclusion of all recognition of heterogeneity of matter, and presents us with the solution of the great problem of celestial mechanics, in which all that is variable in the uranological sphere is subjected to the sole control of dynamical laws.

Periodical alternations of light upon the surface of the planet Mars do indeed point, in accordance with its different seasons of the year, to various meteorological processes, and to the polar precipitates excited by cold in the atmosphere of that planet, (Cosmos, vol. iv, p. 504). Guided by analogies and reasoning, we may indeed here assume the presence of ice or snow (oxygen and hydrogen), as in the eruptive masses or the annular plains of the moon we assume the existence of different kinds of rock on our satellite, but direct observation can teach us nothing in reference to these points. Even Newton ventured only on conjectures regarding the elementary constitution of the planets which belong to our

own solar system, as we learn from an important conversation which he had at Kensington with Conduit (Cosmos, vol. i, p. 120). The uniform image of homogeneous gravitating matter conglomerated into celestial bodies has occupied the fancy of mankind in various ways, and mythology has even linked the charm of music to the voiceless regions within the realms of space (Cosmos, vol. iv, pp. 431-434).

Amid the boundless wealth of chemically varying substances, with their numberless manifestations of force-amid the plastic and creative energy of the whole of the organic world, and of many inorganic substances-amid the metamorphosis of matter which exhibits an ever-active appearance of creation and annihilation, the human mind, ever striving to grasp at order, often yearns for simple laws of motion in the investigation of the terrestrial sphere. Even Aristotle in his Physics states, that "the fundamental principles of all nature are change and motion; he who does not recognise this truth recognises not nature herself" (Phys. Auscult. iii, 1 p. 200 Bekker), and referring to the difference of matter (" a diversity in essence"), he designates motion in respect to its qualitative nature, as a metamorphosis, aMoiwois, very different from mere mixture, μiğis, and a penetration which does not exclude the idea of subsequent separation (De Gener. et Corrupt. i, 1 p. 327).

The unequal ascent of fluids in capillary tubes-the endosmosis which is so active in all organic cells, and is probably a consequence of capillarity-the condensation of different kinds of gases in porous bodies (of oxygen in spongy platinum, with a pressure which is equal to a force of more than 700 atmospheres, and of carbonic acid in boxwood charcoal, when more than one-third is condensed in a liquid state on the walls of the cells) the chemical action of contactsubstances which, by their presence occasion or destroy (by catalysis) combinations without themselves taking any part in them-all these phenomena teach us that bodies at infinitely small distances exert an attraction upon one another, which depends upon their specific natures. We cannot conceive such attractions to exist independently of motions, which must be excited by them although inappreciable to our eyes.

We are still entirely ignorant of the relations which reci

procal molecular attraction as a cause of unceasing motion on the surface, and very probably also in the interior of the earth's body, exerts upon the attraction of gravitation, by which the planets as well as their central body are maintained in constant motion. Even the partial solution of this purely physical problem would yield the highest and most splendid results that can be attained in these paths of inquiry, by the aid of experimental and intellectual research. I purposely abstain in these sentences from associating (as is commonly done) the name of Newton with that law of attraction, which rules the celestial bodies in space at boundless distances, and which is inversely as the square of the distance. Such an association implies almost an injustice towards the memory of this great man, who had recognised both these manifestations of force, although he did not separate them with sufficient distinctness, for we find-as if in the felicitous presentiment of future discoveries-that he attempted in the Queries to his Optics to refer capillarity and the little that was then known of chemical affinity to universal gravitation (Laplace, Expos. du Syst. du Monde, p. 384. Cosmos, vol. iii, p. 23).

As in the physical world, more especially on the borders of the sea, delusive images often appear which seem for a time to promise to the expectant discoverer the possession of some new and unknown land; so, on the ideal horizon of the remotest regions of the world of thought, the earnest investigator is often cheered by many sanguine hopes, which vanish almost as quickly as they have been formed. Some of the splendid discoveries of modern times have undoubtedly been of a nature to heighten this expectation. Among these we may instance contact-electricity-magnetism of rotation, which may even be excited by fluids, either in their aqueous form or consolidated into ice-the felicitous attempt of considering all chemical affinity as the consequence of the electrical relations of atoms with a predominating polar forcethe theory of isomorphous substances in its application to the formation of crystals-many phenomena of the electrical condition of living muscular fibre-and lastly, the knowledge which we have obtained of the influence exerted by the sun's position, that is to say, the thermic force of the solar rays, upon the greater or lesser magnetic capacity and conducting

power of one of the constituents of our atmosphere, namely, oxygen. When light is unexpectedly thrown upon any previously obscure group of phenomena in the physical world, we may the more readily believe that we are on the threshold of new discoveries, when we find that these relations appear to be either obscure, or even in opposition to already established facts.

I have more particularly adduced examples in which the dynamic actions of attracting forces seem to show the course by which we may hope to approximate towards the solution of the problem of the original, unchangeable, and hence named the elementary heterogeneity of substances (for instance, oxygen, hydrogen, sulphur, potassium, phosphorus, tin, &c.), and of the amount of their tendency to combine, in other words, their chemical affinity. Differences of form and mixture are, I would again repeat, the only elements of our knowledge of matter; they are the abstractions under which we endeavour to comprehend the all-moving universe, both as to its size and composition. The detonation of the fulminates under a slight mechanical pressure, and the still more formidable explosion of terchloride of nitrogen, which is accompanied by fire, contrast with the detonating combination of chlorine and hydrogen, which explodes when the sun's rays fall directly upon it (more especially the violet rays). Metamorphosis, union, and separation afford evidence of the eternal circulation of the elements in inorganic nature no less than in the living cells of plants and animals. "The quantity of existing matter remains however the same, the elements alone change their relative positions to one another."

We thus find a verification of the ancient axiom of Anaxagoras, that created things neither increase nor decrease in the Universe, and that that which the Greeks termed the destruction of matter was a mere separation of parts. Our earthly sphere, within which is comprised all that portion of the organic physical world, which is accessible to our observation, is apparently a laboratory of death and decay; but that great natural process of slow combustion, which we call decay, does not terminate in annihilation. The liberated bodies combine to form other structures, and through the agency of the active forces which are incorporated in them a new life germinates from the bosom of the earth.

8

RESULTS OF OBSERVATION IN THE TELLURIC PORTION OF THE PHYSICAL DESCRIPTION OF THE UNIVERSE.

In the attempt to grasp the inexhaustible materials afforded by the study of the physical world-or in other words-to group phenomena in such a manner as to facilitate our insight into their causal connection, general clearness and lucidity can only be secured where special details more particularly in the long and successfully cultivated fields of observation—are not separated from the higher points of view of cosmical unity. The telluric sphere, as opposed to the uranological, is separable into two portions, namely, the inorganic and the organic departments. The former comprises the size, form, and density of our terrestrial planet; its internal heat; its electro-magnetic activity; the mineral constitution of the earth's crust; the reaction of the interior of the planet on its outer surface which acts dynamically by producing earthquakes, and chemically by rock-forming, and rock-metamorphosing processes; the partial covering of the solid surface by the liquid element-the ocean; the contour and articulation of the upheaved earth into continents and islands; and lastly the general external gaseous investment (the atmosphere). The second or organic domain comprises not the individual forms of life which we have considered in the Delineation of Nature, but the relations in space which they bear to the solid and fluid parts of the earth's surface, the geography of plants and animals, and the descent of the races and varieties of man from one common, primary stock.

This division into two domains belongs to a certain extent to the ancients, who separated from the vital phenomena of plants and animals such material processes as change of form and the transition of matter from one body to another. In the almost total deficiency of all means for increasing the powers of vision, the difference between the two organisms1 was based upon mere intuition, and in part upon the dogma of self-nutrition (Aristot. de Anima, ii, 1 t. i, p. 412, a 14,

1 See Cosmos, vol. iii, p. 54.