There are two distinct species of evidence which we are accustomed to employ in the investigation of Natural Truth: the evidence of demonstration and the evidence of analogy.1 To one or the other of these we have recourse in questions to which that direct evidence afforded by the senses, or by testimony, is inapplicable. The first species of evidence, that of demonstration, is of chief utility in the higher physical and mathematical sciences, its office being to reduce observed phenomena to the dominion of fixed laws, and again from fixed and ascertained laws to deduce the succession of phenomena. This induction of laws and derivation of phenomena has constituted in all the more important sciences the labour of many minds, and of successive ages. Thus in the science of Astronomy, it is to Newton that we owe the discovery of the law of Gravitation. It is to him in part, and to the Astronomers of France in the next age in a greater degree, that we must assign the honour of having traced that law to its remoter consequences. It will be seen that the entire process, whether of induction or derivation, rests on the general principle, that there is an appointed order of nature, that her sequences of cause and effect are invariable. Hence, were our means of analysis sufficiently powerful and comprehensive, it would be possible from a knowledge of the existing state of the material universe, to determine its condition at any future period. One of the questions which I have proposed to consider this evening—the question of the stability and permanency of the existing planetary system, is of this character, and to a certain extent admits of being answered by that species of evidence which I have endeavoured to describe. I do not however, when I come to speak of the question, design to offer any special account of the evidence on which it rests. Such an attempt would certainly fail of its object. I shall on that subject restrict myself to a simple exposition of results.2
The second species of evidence to which I have alluded, the evidence of analogy, is of familiar application in the common events of life. It takes not the high and absolute ground of demonstration but confines itself to such affirmations as these—that where we see a likeness of cause or of associated circumstances, we may with some probability infer a likeness of result; that from an imperfectly seen, or partially unfolded plan, we may form some conception of the finished performance. It is manifest that this species of evidence admits of degrees, and that the confidence with which we regard its conclusions will materially depend on the clearness of the observed analogies. It is on such evidence that the question which I shall first consider, i.e., whether the planets are inhabited, must be decided, and the question is one of probability, and does not involve the long and connected chain of reasoning in which demonstrative evidence usually consists—it is obvious that it belongs to all, when in possession of the necessary facts, to form a judgment for themselves.
In order then to prosecute the analogy, we shall first consider the general conditions to which life as here manifested, appears to be subject; secondly, the adaptations of the earth as the abode of life; and lastly the presumptions in favour of such adaptation on the part of the remaining orbs of the planetary system.
Now the most striking characteristic of life, whether animal or vegetable, as developed in this planet is its periodicity—the circumstance that it is marked by alternate periods of action and repose. The sleeping and waking life of animals is a great illustration of this fact. Many plants, it is observed, shut up their leaves at the approach of night, and extend them with the dawn, and it is perhaps true of all, that the functions which they exercise during the hours of darkness, are different from those which are carried out under the influence of light: the exceptions to this remark, if any, are so few, and as doubtful, that we are, I conceive, justified in assuming that this alternation of opposing states, this constant order of successive activity and remission, is a law of organized beings as manifested here—a necessity to which all the tribes of earth are subject.
Another characteristic of the life around us, and one that is closely connected with the general law we have just noticed, is, that the animated structure, passing through certain appointed stages of renovation and decay, tends finally to dissolution. The dominion of this law is universal. Such however may not be the condition of life in the abstract, it may be merely an accident of its present state.
We may, and often do, conceive of life as manifesting itself according to a different law, not needing repose, not subject to decay; but this is not the character of terrestrial life, nor could it be, so far as we can judge of the adaptations of our present abode. Let us consider what those adaptations are.
In the first place, the revolution of the earth on its axis, and the consequent succession of day and night, is an evident adaptation to that law of the animal constitution, by which it is subject to the necessity of repose. Again, the presence of a surrounding atmosphere seems to be clearly adapted to that condition of perpetual renovation and decay in the animal structure, to which I have called your attention. The earth might have been formed without an atmosphere, and the various tribes of animal and vegetable nature might have been created free from the need of that purifying and stimulating influence, which the air perpetually administers. But for wise ends it has been ordered otherwise, and what I wish to remark is, that between the two arrangements in question, there is a connection not certainly of cause and effect, but of mutual adaptation. I might here observe on several other points of relation, but those we have considered are the most important, and the others will be noticed in the sequel.
Now the first point of the analogy which I propose to trace is, that so far as we are able to judge, every planet of the system revolves on an axis, and is enveloped in an atmosphere. The sun revolves in 23 days, but to him of course, there is no vicissitude of light and darkness. He moves surrounded with perpetual day, environed at the same time by an atmosphere of immense extent. Mercury and the other planets in their order revolve, but in different periods: Venus and Mars in nearly the same as the earth, Jupiter in 10 hours, Saturn in about the same time; those periods making the respective lengths of their days. The moon and all the satellites revolve around their own axes in the same period in which they accomplish their revolutions around their primary planets. Thus the lunar day is of the duration of a month.
The existence of the planetary atmosphere is detected in various ways, sometimes by the appearance of twilight on the planet, or evening shade separating its dark and its perfectly illuminated hemisphere. Sometimes its presence is shown by the burden of clouds and vapours which it supports, and sometimes by peculiar optical phenomena which are exhibited when the planet surrounded by an atmosphere passes over a fixed star or satellite, or over the rim of the sun disk. By one or more of these methods, for all are not applicable in all cases, has the existence of an atmosphere been proved in every orb that is not either too small, or too distant for sufficiently accurate observation. Venus for example has a very extensive atmosphere. The twilight, which borders her sun lighted realms, has in certain positions of the planet been distinctly seen. Mars is surrounded by an atmosphere of greater density, and Jupiter and Saturn have each a like appendage. The atmosphere of the moon is very rare, and of small extent. Indeed it is probable that in various respects, the constitution of the satellites differs from that of the primary planets.
Another condition which appears necessary to the maintenance of animal and vegetable life on this planet is the presence of water. For the supply and distribution of this important element, it is requisite that the earth’s surface should be indented by oceans, diversified by hill and dale, spread out into extended plains, and crossed by lofty mountains. The water systems of continents and large islands depend in a great measure on the positions and magnitudes of their mountain chains. It is to this cause that we must ascribe much of the difference which exists between the green savannahs of America and the African deserts, between the well-watered plains of Europe, and the thirsty wilds of Australia. Let us then consider the evidences which favour the existence of water, and of a diversified surface, on the sister planets. The facts which observation has presented bearing on this question are the following.
On the disc of the planet Mercury, dark greyish spots have been observed, but from its distance and proximity to the sun, their existence only is known. The presumption is, that they are mountains.
Venus has unquestionably mountain ranges of great extent, probably much greater than any existing on the earth’s surface. These are found to be invariable in form and position. The edge of her enlightened portion, like that of the moon, is broken and irregular. The horns are sometimes seen to be rounded off, as if, says Prof. Nichol, by the shadow of a line of eminences.3 Bright points are observed within the boundary of her dark region, the peaks undoubtedly of isolated and lofty mountains. Her atmosphere supports clouds, the true character of which is shown by their change of place and varying aspect. Of course it is only by telescopes of extraordinary power and excellence, that these phenomena are revealed to our gaze.
The surface of the planet Mars is divided into distinct regions, which are marked respectively by a reddish and a greenish tinge. The former are supposed to represent continents, the latter oceans. It is established, that the relative positions of these do not change—that their boundaries are invariable. Thus it has been found possible to delineate on a map the surface of the planet. In support of the opinion that Mars is possessed of water, or of some similar fluid, there is another fact of a very striking character, which I shall briefly explain.
We know that during the winter of our hemisphere, the North Pole of the earth is enveloped in frost and darkness. During that period, there is a very great accumulation of ice, partly in the Arctic seas, and partly in the larger rivers of Siberia and of Northern America. At the same time the frozen soil is covered to a great depth with snow, which indeed is nature’s provision, affording to the dwarfed and stunted vegetation of those regions its only protection from the clemency of the season. With the coming in of the Spring, the Pole emerges into the light of the sun, the frost-bound deep is loosed, the snow disappears, and the ice is drifted by currents into warmer seas. Thus the limits of that wintery domain which girds the Pole are gradually contracted, until the revolution of the seasons restores it to its former dimensions.
Now there is reason to believe that this condition of things has an exact counterpart on the planet Mars. As either pole emerges from darkness, for Mars like the earth has its order and succession of seasons, it is observed to be surrounded with a brilliantly white covering, the dimensions of which are gradually contracted during the period in which it remains exposed to the action of the sun’s rays, until it totally disappears. To what shall we attribute this remarkable phenomenon, if not to causes like those, which on our own planet are productive of similar effects? If the white circle in question is not of the nature of ice or snow, why does it manifest itself at the poles, and why is it impatient of the summer? On the other hand, if it does possess the character which we have supposed, how close, how intimate, is the analogy which binds the remote orb of Mars to the earth we tread.
Between Mars and Jupiter revolve the asteroids, four small planets which occupy the place of a larger one. Of their physical constitution nothing is known, unless we suppose with some that their origin is connected with that of meteoric stones, and thence infer a likeness of internal structure. Now aerolites do not, so far as I am aware, contain any elements which are not found as a constituent of our globe, though the combinations are different. Sometimes they consist of malleable iron, with a small portion of that rare metal nickel. Of this kind was that vast mass which fell near the river Genesei, and which the wandering Tartars regarded with superstitious dread. Captain Owen I think mentions a district in south Africa, over which a shower of meteoric copper is believed to have fallen.4 That these bodies come to us from the planetary spheres, admits scarcely of any doubt, and whether they indeed originated in the event which gave birth to the asteroids or not, they to a certain extent afford a presumption, that the elementary constitution of the other planets is similar to our own.
The planet Jupiter, viewed through a telescope of moderate power, appears surrounded by a series of belts, or of shaded lines parallel to his equator, and separated from each other by broad white spaces. It is generally thought that these intervening spaces are clouds, and that the belts are portions of the dark body of the planet seen between them. As the appearances are among the most remarkable which observation has presented to us, I shall endeavour to explain their supposed origin.
In obedience to a well-known law, the great body of the atmosphere in the frigid and temperate zones of the earth has a tendency to move towards warmer regions, and a like tendency affects the waters of the oceans. As the two great currents approach the equator, they take a westerly direction; for as the velocity of the earth’s rotation from west to east is greatest at the equator, and as the currents on their arrival there do not partake of the same motion in an equal degree, they—so to speak—fall behind their place, and produce a general current both of air and water in the opposite direction, i.e., from east to west. In the ocean the current is sometimes impeded, and its direction changed by the presence of continents and large islands. Thus the great easterly current of the Atlantic perpetually setting into the gulf of Mexico is turned aside into the North Atlantic and forms the well-known Gulf Stream. In the air however the general easterly current is less subject to this interference, and under the name of the trade winds prevails round the globe. Particular interruptions do indeed occur, as in the Indian Ocean, when the heated planes of the Hindustan produce—if I may be allowed the expression—a trade wind of their own. Such exceptions apart, it may be said, that an east wind prevails on either side of the equator throughout the year.
Now on the surface of Jupiter, the causes which here produce the trade winds operate with tenfold power. Notwithstanding his vastness, it is ascertained that he revolves in 10 hours. This prodigious velocity of revolution has even sensibly affected the form of the planet. I say sensibly, for while the forms of all the planets have been thus modified, it is on Jupiter and Saturn alone that the protuberant equator and flattened poles are apparent to the eye. Produced by the same cause, his trade winds must in like manner exceed ours in strength, and extend not merely over a strip on either side of his equator, but over a large portion of his surface. It is then [not] unreasonable to suppose that his atmosphere, burdened with clouds, should present the appearance we have noticed, and indicate by their arrangement the duration of his prevailing winds. It is a confirmation of this view, that his supposed clouds have been seen dispersed over the surface, and that dark spots are observed (probably mountains) in the belts, but never in the white spaces between them.
The same thing will apply to the belts of Saturn which differ from those of Jupiter only in that they are of a more uniform character and less subject to change.
I have mentioned the existence of dark spots on the planets supposed to represent mountains. Assuming that they are such, it is an interesting point of inquiry whether those causes which have upheaved the Alps and Andes of the globe have operated with like effect on others. Our own satellite affords us to a certain extent the means of answering this question.
We know that in some parts of our world the volcanic energy operates with unceasing activity. The manifestation of this we recognized in the earthquake, another in the burning mountain. We are assured too that it was by this agency that infinite wisdom saw fit to work when preparing an abode for man. It broke up the stony crust of the earth and piled out of its fragments the everlasting mountains. Extinct craters on almost every line of eminences betokened the manner of its origin. Now that particular form of the volcanic energy which we observe in the eruptive crater, manifests itself in two ways. Sometimes it acts along the line of disturbance. Of this we have an example in the Andes; another in that chain of volcanic islands which skirts the entire Eastern shore of Asia, and presents a line of burning summits, extending from the polar seas to the equator. Sometimes again it acts around a centre of disturbance. Now to whatever extent this agency has been developed on the earth, there can be no doubt that its action has been much more general on the moon. Viewing her through a powerful telescope, we imagine that an amount of volcanic power, equal to that which has been expended on the entire crust of the earth, had been shot up in her lesser orb, and bursting from its prison, and so riven and shattered her outward frame, and so deeply pitted and corrugated her surface, as to leave nothing to the eye of the spectator but a wilderness of rocks and craters; and that the causes we have supposed, the volcano, and that which we call earthquake, have indeed produced the effect, is rendered the more probable by this one circumstance: Amid all their scouring disorder the same general laws are recognized in the deposition of the lunar mountains and craters, as in the arrangement of our own. We see then the distinction to which I have adverted between lines and centres of disturbance. In some cases we find the two forms associated, as when a series of volcanic ridges radiate from a central crater. Many other clear analogies have been observed, of which I shall here only notice one. It is the property of all the great mountain chains on our planet, that on one side they present a steep and bold escarpment, on the other a gradual slope. Thus the mighty range of the Himmaleh [i.e., Himalayas] rises like a rocky barrier from the sheltered plains of India, but descends by a gentle declivity to the elevated steppes of Central Asia. Now the same property is said to belong to the lunar mountains. Taken in connexion with what I have remarked respecting the existence and arrangement of lunar craters, it seems to point out most clearly a similarity of the causes by which effects as similar have been evolved.
To the above statement it might be added that some observers assert with confidence that they have seen a bright light shining for a short period on the enlightened part of the moon’s disk and gradually fading away. This has been supposed to be connected with a volcanic eruption. Others have imagined that they saw coruscations of electric light resembling the aurora borealis on the dark hemisphere of Venus, but further confirmation of the existence of this phenomenon is perhaps needed.
It will have been observed that many particulars of the general analogy which I have endeavoured to trace between the earth and the other planets do not apply to the moon. For want of water, the extreme rarity of her atmosphere, the total absence of those traces which the congregation of rational and intelligent beings on her surface might be supposed to have wrought, preclude us from affirming with any colour of probability that her orb is the seat of life. At the same time it may be proper to notice that some of her deeper and more sheltered valleys are said to reflect a green light which may for aught we know be the hue of vegetation. Considering how slight are the probabilities in favour of her being inhabited, it may be asked, why I have been so anxious to establish a relationship between her mountains and our own. I answer by remarking that on account of the immense distance of the primary planets we cannot hope to ascertain by observation to what cause the elevation of their mountain ranges is due. But if it can be shown that the process is the same in our satellites as it is here, there is good reason for supposing that the law is general and that it embraces in its operation the remaining planets of the system. Taking this view in connexion with the proved existence of water or of some similar fluid on their services, we see that their physical geology must in its principal features resemble our own. There is the same upheaving central force, the same abrading and dissolving agency. May we not extend the analogy and suppose that on the floors of their oceans are being deposited the strata destined to emerge in future continents and to preserve in enduring archives of stone the records of past changes?
We have now traced the general features of the analogy which was proposed to be considered, so far as observation has yet revealed them to us. In one or all of the planets, we have found evidence of the existence of clouds of water or of some fluid possessing similar properties, and of an atmosphere. Their surface, we have seen to be diversified with hills and valleys, and in one instance at least to present a supposed division of seas and continents: we have observed ice gathering around their poles, and currents like our trade winds manifesting themselves in the arrangement of their equatorial clouds. Their internal constitution we have reason to think similar to that of our own planet, though differing in respect of greater or lesser density; the agents of their physical changes are similar also. And now arises the question, to what final object does this analogy point? Are we justified in inferring that the planets were constructed to be habitations of life?
It is obvious that the inference supposed is the most natural one. If we discover on other planets such arrangements as on our own have a manifest adaptation to the wants of organized beings, it seems perfectly agreeable to our common modes of thinking to suppose that the planets are inhabited also. Let us examine whether there are grounds on which such a deduction may be formed as a logical and necessary consequence.
I think that the possibility of doing this depends on the admission that the universe is the work of an intelligent being, who acted not capriciously, but on fixed and immutable principles. Without this admission, I do not see how conclusions drawn from one part of the general system can be applied to another part. The ground of connection between those parts consists in this—that they have one common Author. And it is on this ground alone that we can maintain any deductions from the analogies which they present. Viewing the universe thus, in relation to its Author, we may from observation upon those parts of His works with which we are most familiar, derive some knowledge of the principles by which He has thought fit to direct the exercises of His creative power in reference to the whole. The conclusions which may with safety be drawn are, I conceive, the following:
From the fact that nature is governed by general laws we may infer that its Author acts by general rules, and hence, that in those parts of the universe which lie beyond the sphere of our observation, the same government of fixed laws is maintained. We have a remarkable illustration of this truth in the fact recently established that the law of gravitation extends to the fixed stars, where lesser suns revolve around greater, as the moon around the earth.
From external nature, and from innumerable examples in the animal and vegetable economy, we may infer that the Creator in the accomplishment of his designs, operates by secondary means, which are for the most part intelligible and uniform. The evidence of design and adaptation are indeed so palpable that the object of contrivance can in very few instances be mistaken. From the fossil remains of extinct animals, Cuvier inferred their forms and habits.5 The confidence which we attach to the results of such inquiries rests on this—that we believe there are evidences of design even in the structure of a bone, or the convolutions of a shell, and that the object of the design may be inferred from the uniformity of general principles by which all the Creator’s works are characterized.
From the present condition and past history of the earth, we may infer that it was specially designed by its Author to be an abode of life—not of life in mere subservience to the wants of man, but of life accomplishing in innumerable tribes of animated beings, its proper purpose of activity and enjoyment. The view which most faithfully represents nature, and most truly interprets the declarations of Holy Writ is, that there had been exceptional interpositions of creative power peopling the earth with successive races of beings adapted to its changing condition. Prodigious as is the development of the powers of life at the present time, it may be doubted whether it is equal in extent to that of remote eras. How exuberant must’ve been the vegetation from which the veins of coal were deposited! How great the abundance of animal life which covered with bones of elephants the inhospitable shores of Siberia, and keep them into vast accumulations on the islands of the polar sea!! But it is not only with respect to the larger forms of life that this prodigality of nature has been manifested. The discovery of the fossil infusoria of slate, establishing that extensive beds of that substance consist merely of the remains of animalcules, similar to those which are now found in stagnant waters, is a fact pregnant with instruction.6 Again that mysterious law, by which the decay and dissolution of one animal structure supplies to countless others the means of existence, and death administers to life, shows in an extreme case how wide is the dominion given to the latter. It is not affirmed that the maintenance of life was the sole object for which the earth was called into being, but we are justified in asserting that such was at least the chief design of its Author.
Now if these conclusions are admitted, if it is granted that the Author of nature acts consistently in all his works, and that he accomplishes the purposes of his will by special means and adaptations, that his purpose with respect to the earth is, that it should be an abode of life, and that the mass and adaptations by which that purpose is accomplished are employed in other worlds, I see not how the conclusion is to be resisted, that those other worlds are intended to be habitations of life also. Refusing to admit the inference, we fall on such contradictions as these: that he acts inconsistently whose character is immutable; that he has created worlds without end or object, who made nothing in vain; that he has chosen to preside over an empire of death, who is the source and fountain of life and enjoyment.
I have observed that in maintaining that the planets are constructed to be abodes of life, we do not assert that this is the only object for which they were created. It is characteristic of the Creator’s proceedings, to accomplish many purposes by one system of means. We may thus conceive that while each planet is to its own inhabitants an abode of life, it may be designed to answer important ends in respect of the other planets. The science of navigation which is of such great consequence rests almost exclusively on astronomical observation. Again, a planetary system is a mechanism so wonderful, that we may suppose one design of its formation to have been, to display not simply the vastness of creative power, but in a more eminent degree, the resources of creative wisdom. That refined and efficacious instrument of thought, the modern analysis, has chiefly arisen out of the study of the planetary arrangements. It may thus be imagined that the material universe has been adapted by its author not only to the physical but also to the intellectual constitution of his rational offspring. We might pursue these speculations and inquire whether there are not also examples of adaptations to the moral, as well as to the intellectual and physical, constitutions: as for example, whether there is not an analogy between the government of material nature by fixed laws, and that of moral agents by the unalterable rule of duty. I merely notice these as questions, which although they may not lead to definite conclusions, can hardly fail of affording interest and profit.
We have now considered the designs for which the planetary system was called into existence. It remains only to inquire whether it possesses the element of stability
There is reason to suppose that the planetary system has not always existed in its present state and form. It may once have been in the condition of the nebula, like perhaps to that which shines with a different and irregular splendour in the constellation Orion. Out of this formless and chaotic state may have gradually been evolved the order and harmonious arrangement which it now presents, a system of lesser orbs revolving around one predominant mass, in paths differing little from circles in the same direction, from west to east, and in nearly the same plane. The question to be considered is, whether this is the final condition of the system—whether, natural causes alone considered, such an order of things will always prevail. The results which the highest application of mathematics have yielded in reference to this question are the following:
First. One planet revolving around one central sun, through space, void of resistance, would constitute an undisturbed and permanent system. The planet would revolve in the same orbit, and with the same relations of distance and velocity forever.
Second. One or more planets revolving under the same conditions around a central sun, would constitute a disturbed but permanent system. The system would be a disturbed one, because each planet would, by virtue of its attraction, interfere with the motions of all the others. It would be a stable and permanent system, because all the irregularities of mutual disturbance would be confined within narrow limits. Increasing to a certain extent, they would afterwards diminish, and diminishing again, increase in such manner, that the system could never depart far from a mean state. If the orbit of the planet is at one period dilating, as is now the case with the earth’s orbit, it will subsequently contract. If the inclination of the orbit’s plane to the plane of the equator is diminishing, and such is the condition of the earth’s now, such diminution will be followed by increase. The dilation of the earth’s orbit, could it forever continue, would indefinitely lower the mean temperature of the year. In like manner, the other irregularity which I have named, would eventually abolish the distinction of seasons. Both have however their determined bounds which they cannot pass. All the perturbations of the planetary system produced by mutual attraction are of a self-correcting character. The unassisted intellect of man has achieved no higher triumph, than in establishing this great principle of the economy of the universe.
Third. Planets revolving around a central sun through a resisting medium cannot constitute a permanent system. The effect of the resistance in any given period may be but slight, perhaps imperceptible; accumulated through indefinite ages, it will cause each planet to revolve in a lessening orbit, and gradually to approach the sun. When once the existence of a resisting fluid in space is established, the doom of our own planetary system, and of all others, may be regarded as settled. Nothing short of a special interference with the laws of nature can avert its coming. The question then of the stability of our system ultimately rests on this: whether the planetary spaces are filled with a resisting ether or not. Reasoning from natural causes, we should say that if there is such an ether, the present arrangements of the universe exist but for a determinate period. If there is not, they may, unless other agencies interfere, endure to eternity.7
Now an opinion in favour of the existence of an ethereal fluid diffused through space has been very prevalent and it rests on two distinct kinds of evidence. It is thought to be proved by certain phenomena connected with the action of light, and also by observations on Encke’s comet.8
With respect to the first species of evidence, it is now generally believed that light is produced by the vibrations of a highly elastic and refined ether, as sound is produced by the vibrations of the air. The facts on which this theory is founded are very numerous and consist of a great variety of phenomena observed under different circumstances, as when light passes through narrow apertures, or is transmitted through crystals and precious stones, such as Iceland spar, the amethyst, [and] the topaz. These results it is thought can only be explained on the supposition that there is an ether diffused through space, as vibrations, propagated with inconceivable rapidity, excite through the medium of our visual organs, the sensation of light.
Encke’s comet is nothing more than an attenuated luminous vapour, revolving round the sun, in about three years and a half. If on any body, the effects of resistance could be perceived, it would be on one like this. Accordingly it is said that such an effect has been observed, and that the resisting ether is thereby rendered actively manifest. But it is to be remarked, that no effects of resistance have been traced in the motions of the planets. The disturbances produced by their mutual attraction were observed even before the cause was understood. They have been made the subjects of calculation, and enter into the construction of the most accurate tables. But the effects of resistance, constantly accumulating from the earliest period of accurate observation, are still imperceptible. This does not prove their non-resistance, but only shows that they are so slight, as to require the lapse of far longer periods before they can sensibly interfere with the existing arrangements of the universe.
From the above results I think we are entitled to infer that the planetary system may exist through periods of duration inconceivably great, but that it is not constructed for eternity. Indeed it is probable that there is no combination of things in the material universe to which eternal duration can with propriety be ascribed. We do in a certain sense speak of the eternity of the visible heavens, and we sometimes apply such modes of expression to describe the least perishable of the movements of human power, but it is only figuratively, and by comparison with the shortness of our own lives that this language can with any propriety be used. The physical agencies which under divine appointment have educed from a chaotic state the shining order of the heavenly frame would alone suffice for its dissolution.
We have however no right to affirm that the dissolution of the system will be left to the slow though certain operation of the physical causes which we have considered. The period which they would require is so incalculably great that long ere it shall have elapsed, all the designs for which the planetary worlds were called into existence may have received their final accomplishment. The power which has interposed to create, may be interposed again to destroy, and to create anew. The traditionary belief in all ages has pointed to a destruction by fire of the present order of things. This was the doctrine of some of the ancient philosophical sects in Greece, and it is finally alluded to by Ovid.9
An authority higher than that of Grecian sage or Roman poet has told us [of an]other day “in the which the heavens shall pass away with a great noise and the elements shall melt with fervent heat.”10 We should err if we should suppose that a declaration like the above is given us for the purpose of gratifying an idle curiosity as to the manner in which the great designs of Providence are to be realized, but we may lawfully receive it as an intimation that the existing constitution of material things is to pass away and to give place to a higher. The discussion of such questions does not however fall within the province of natural philosophy. It is well for us to know where that study should begin and when it should end. One of the best lessons it can teach us is, to trust, in things unknown, the wisdom and benevolence which are conspicuous in the things that are known.