God's glory in the heavens/The Structure Of The Planets
Broken Appearance of Saturn's Rings.
THE STRUCTURE OF THE PLANETS.
Were a city, in the heart of Africa, bombarded by an enemy employing the deadly projectiles of modern warfare, it would be possible for the besieged, though they had never before seen such objects, to discover, when picking them up, a unity of purpose. The Armstrong bolt and the Minié bullet, however different in appearance, would be found to be essentially the same in structure and design. Both are alike constructed to pass through the air with the least resistance. The marks of the rifling would tell the inquirer that this contrivance served the same purpose as the feathering of his own arrow—steadiness of flight. Were he to examine the Moorsom and the Armstrong shells, he would find a corresponding similarity, with the same object to be served—the bursting of the shell at the moment of striking. Amidst the diversity he would discover unity of plan. It is this synthesis of diverse elements that communicates such a charm to the study of the works both of God and man. The child takes a delight in tracing fanciful resemblances; the matured mind finds its enjoyment in discovering latent but real analogies; and to the devout mind, these analogies are so many steps of the pyramid, leading to the apex—the divine unity that synthetises all diversity in nature.
We have already examined the structure of the sun. We have pried into the central furnace, and seen how curiously complicated its structure is. We have seen its surging flames, and the edges of its concentric strata, appearing like the bars of a mighty furnace. Our object is now to shew, that the sun and planets belong to the same family, however diverse they appear to be. We speak of the sun as if separated from the planets by a wide gulf, and as if belonging to a totally distinct class of bodies; but we M shall find more points of resemblance than of difference.
The central position of the sun may seem to claim for it a distinctive character, but it is really only the last of a series. The link that terminates a chain is nothing: more than a link. The innermost case of a mummy is only a mummy case, though painted with brighter hieroglyphics. The last of a nest of boxes enclosing a jewel, though immediately enveloping the precious object, is only one of the set. The centre of the solar system is the jewel, and the sun revolves around it just as the planets do. The only difference is, that its circle is the narrowest.
It may be urged that the structure and constitution of the sun completely separate it from the planets, but there is evidence to shew that there is a type to which the planets and the sun equally belong. The sun, no doubt, is an intense furnace, while the planets are in themselves dark bodies, but the structure may be still alike. If you saw only one furnace in action at an iron-work, you would not conclude that the others, which have been put out, belong to a quite different class of buildings. The hot-blast apparatus, the tuyeres, the furnace-bars, the well, and the slag before the furnace, would at once shew the purpose of the erection, and prove that it had been used as a furnace. Though the sun is now the only body of the system in active operation as a furnace, there are evident indications that the planets were at one time incandescent bodies. Geology gives abundant proof of igneous action in our globe at a former period, and we have reason to believe that we now stand on a crust floating on a molten sea. When we look to the moon J we find innumerable extinct volcanoes, like so many furnaces in an iron district, put out by a general strike. The other planets do not allow us to see their minuter features, but analogy fairly leads to the conclusion that they were all, at one time, active furnaces.
The concentric envelopes of the sun are, by no means, a distinctive feature, or one that should separate it from the family of planets. The rings of Saturn are* only a special case of this concentricity — the ring being merely a flattened sphere. The envelopes of the sun are somewhat flattened, and Saturn's rings are only an extreme case. The spherical mop, when twirled, becomes a flat ring, so that the mere circumstance of motion explains the difference. The sun has, indeed, rings similar to those of Saturn. We have seen that the zodiacal light, and the zones of asteroids and meteorites are analogous to these rings. The earth also afl'ords an example of the concentric structure. In an eclipse of the moon, an inhabitant of that body would behold a spectacle similar to what is presented in a solar eclipse. He would see a faint corona, and, along the margin of the earth, he would see a copper-coloured stratum, with prominences like the rose-coloured shell of the sun, this stratum being the lower regions of the air loaded with moisture and clouds; and were he to see down through the crust of the earth, he would in all probability discover a concentric arrangement of the interior.In the case of Jupiter and Saturn, it is obvious that we see only the outer shell, within which the bodies of the planets are concealed. The disc of Jupiter presents very singular phenomena. There are indications of constant commotion, and the markings of the belts often present very perplexing forms, of which no account can be given. We only know that the visible disc is not a fixed and solid crust. It is like the visible envelope of the sun, which conceals the solid nucleus in its interior. The shadows of the satellites are seen as dark spots when they cross the disc of the planet, and the satellites themselves can also at the same time be detected by powerful telescopes. Besides these, there are other spots of which no account can be given. They sometimes appear in clusters, as shewn in our figure of the planet. They have a proper motion like the spots on the sun, and, probably, are due to the same general cause—the rotation of the body combined with the higher temperature of the equatorial regions. They will, therefore, correspond with the circular storms or cyclones in the atmosphere of our globe. There is no evidence that we have ever as yet seen the kernel within the outer shell of Jupiter. The usual explanation of the dark belts of Jupiter is, that
they are the more transparent parts of Jupiter's atmosphere, while the brighter parts are the region of clouds which reflect the light more abundantly. In this hypothesis, we see the body of the planet down through the transparent region of dark belts; but it is more probable that, in the dark belts, we see only a part of an interior shell, and that the real body may He far beneath. The dark belts would, in this way, correspond to the penumbra of the spots in the sun, which is only an micovered part of the stratum immediately under the luminous envelope. Jupiter is by far the largest of the planets, and yet it may have only a small solid nucleus. Though, taken as a whole, Jupiter is not heavier than a sphere of water of the same size, we can readily suppose the real body of the planet to be of much heavier matter. It may be compared to a bullet of lead forming the core of a sphere of cork. Dr Whewell's argument then is of no force, when he holds that Jupiter can only be the abode of molluscs, and other lower forms of life suited to a watery abode. Even though the body of Jupiter had only the density of water, it would not at all be necessary to assume that it must necessarily be fluid, for we know of many solid substances as light as water. But there is no necessity for holding that its density is only that of water. The Jovial ball may be as dense as that of the earth, and may afford to the teeming inhabitants as sure a footing as our roads and streets.
How astonishing must the sight of Saturn have been to Galileo when he first descried its strange form! It was, however, long before the character of the monstrosity was understood. A telescopic power as small as that which Galileo used, is sufficient to convince any one, at the present day, that there is a ring round the body of the planet; yet Galileo did not see a ring. He called the parts of the ring, projecting on each side of the planet, ansæ as they appeared like the two handles of an antique vase. We may see nothing more at the present day, and yet every schoolboy would at once know that they are only parts of a ring seen obliquely; and would maintain that he was indebted only to his sight. This is only one illustration of a thousand, that, for what we see around us, we are as much indebted to the intellect as to the eye. The organ of sense gives only skeleton forms, which the intellect and imagination fill up. When shewing objects through a microscope to one unaccustomed to the use of it, you are sometimes astonished that he does not see what is so obvious to yourself; but the mere objective nucleus is unmeaning, unless the previously trained mind can clothe it with significance. It is sometimes matter of surprise that men, living amongst the beautiful and interesting scenes of nature, should be totally uninfluenced by them; but the truth is, the objects that interest us, may not be really seen by them. For thousands of years, the spots on the sun, and the zodiacal light, must have impressed an Image on the human retina, and yet we have no evidence that they were ever really observed till modern times. Another case, still more in point, is the obscure and innermost ring of Saturn. It must have been often pictured on the retina of observers, and yet it was not really observed till a few years ago. Some, indeed, suppose that it must have been developed in recent times, but the ordinary laws of observation furnish us with a sufficient explanation.
When the rings of Saturn were fairly descried, the structure of the planet must have appeared still more marvellous. How contrary to all preconceived notions of the stars! But no sooner is the human mind struck with astonishment, than it seeks to divest the wondrous object of its singularity. There is an instinct that makes us seek for points of similarity. The idea of one presiding intelligence leads us to the conviction, that, however strange the phenomenon may be, it must be in harmony with the other works of God, and this, not merely in reference to adaptation, but to style. Every architect must conform to certain structural rules, without which he cannot erect any edifice; and we find design and adaptation in every building. But, over and above this, there is the undefinable idea of style, and we expect, amidst all diversity, to detect the manner of the man of genius. Genius confers a unity on works of the most diverse structure, and design. We expect to find this unity in the style of God's works, apart from mere adaptation. But is it possible to detect a unity of structure in the solar system, when we have the singular and startling exception of Saturn? Is it really in gear with the other parts of the solar system, as far as style is concerned? It is to this interesting point we would now address ourselves.
Laplace attempted to establish a unity and a type by means of the nebular hypothesis. He conceived a mode by which the planets were manufactured, as the potter fashions artistic vases from the shapeless mass of clay. But our design is not to imagine a unity of process or development, but to detect a unity of result. We can detect the predominating style of Wren, though we are quite ignorant as to the precise mode of operation adopted by him in rearing St Paul's and other edifices. So in the architecture of the solar system, we can discover a plan independently of any theory of evolution. In like manner, we are not obliged to adopt the theories of Lamarck and Darwin in order to accept the fact of archetypes in natural history. Owen's results are altogether independent of such theories.Is there, then, apart from all theories of development, a general style of architecture in the solar system, to which the structure of Saturn conforms? We think there is, and that there is a traceable gradation of distinctive characters through all the planets. The
THE GREAT COMET OF 1858.
fish is the lowest form of the vertebrate type of animals, and the scale upwards to man is marked by the differentiation of limbs. They are undeveloped in the fish, and they rise, through innumerable steps, to perfection in the human species. Comparing the solar with the vertebrate system, the moon, with its naked ball, may represent the undeveloped form of the fish, and Saturn the highest form of vertebrate animals. When we speak of the typical perfection of a planet, we do not at all refer to its adaptation to life. We mean merely the degree in which the distinguishing characteristics of a general style are exhibited. The grand characteristic is the concentricity of structure, which we before traced in the sun. In the sun, we have seen that there are successive envelopes or shells around the core. Three of these were recognised before the last total eclipse, and the phenomena of the eclipse have clearly established, what was before surmised, another envelope of rose-coloured matter; and, extending beyond this stratum, there is the corona, which is, most probably, the atmosphere in which all the others are suspended, like strata of clouds at different heights of our atmosphere. If we accept the hypothesis of the Astronomer-Royal, that the corona is due to our atmosphere reaching nearly to the moon, we shall be forced to admit that this atmosphere exists as a zone or ring encircling the earth. It cannot be the ordinary atmosphere of the earth. Well-known dynamical conditions forbid this supposition. We must suppose it of a nature similar to that of the faint ring of Saturn. This idea would countenance the opinion held by some astronomers, that the zodiacal light is an appendage of the earth and not of the sun. There are, however, inexplicable difficulties in the supposition that the zodiacal light is a nebulous terrestrial zone. Whether we refer it to the earth or sun, it stands as an element of concentric structure.We have reason to believe that Saturn, as well as Jupiter, is constructed on a similar concentric plan, and that his belts are indications of an internal envelope. But does the similarity between the sun and Saturn cease here? By no means; the grand peculiarity of Saturn has its analogue in the sun. Saturn has a series of concentric rings, but so has the sun. Where are they? it will be asked; we have no hesitation in answering that the zone of asteroids between Mars and Jupiter, as well as the zodiacal light, are fairly analogous. Take the bright rings of Saturn, and let us compare it with the zone of asteroids. These rings have all the appearance of being solid bodies, when you take only a cursory glance, but on more minute inspection, proofs leading to an opposite conclusion will be found. There is only one large dark division, but a smaller one at both ends of the ansæ dividing the outer ring into two, is sometimes seen. The views, however, are so capricious, that the observer is naturally led to the conclusion, that there are changes going on in the constitution of the rings. Again,
some have observed a structure in the whole breadth of the rings, similar in appearance to a flat coil of rope, or the ribbed texture of corduroy, rendering it probable that the rings are composed of small bodies closely packed and arranged like concentric strings of beads laid flat on a table. The bodies, on this hypothesis, have no rigid connexion, and move in independent orbits. They are, however, so closely packed together, that they appear as one body. The zone of the asteroids quite corresponds to this. Seventy-one have already (1861) been discovered; and it is probable, from the rate of discovery, that there are thousands upon thousands within the circumscribed zone. To an eye properly situated, and at a sufficient distance, this zone would appear as a faint ring. If more compressed, they would be bright, like the rings of Saturn. These asteroids are probably of every size. Some are large as a kingdom or a county; others are miniature worlds, of the size of Arthur's Seat; and some may dwindle down to the magnitude of a cannon-ball. We may suppose them so arranged as to leave gaps corresponding to the divisions of Saturn's rings.
Again, the obscure ring of Saturn may be compared to the zodiacal light. It will be seen from our figure of the planet, that the recently discovered ring is transparent, as the limb of the disc is seen through it. It is most probably composed of some discrete substance like dust, as it does not comport itself like a gaseous body. This is probably also the constitution of the zodiacal light, which is another ring or zone nearer the sun, the boundaries of which are not well defined. It is shaped somewhat like a quoit. The sun being in the middle of the central hole, we see only the edge of it when it appears to rise as a long cone from the horizon. It is best seen in February and March above the part of the horizon where the sun has set. The generally received opinion is, that it is composed of meteoric bodies; and some hold that it may extend beyond the orbit of the earth, so that we pass through it twice a year. The meteoric bodies become incandescent when they meet our atmosphere, and the two annual periods of meteoric showers are accounted for by the intersection of the earth's orbit at two opposite points. To an eye at a great distance, the sun would appear as if surrounded by two faint rings, with a wide, dark space between, while the outer ring, or that of the asteroids, would likely be subdivided by smaller dark lines.
The calculations of Leverrier, and the discovery of Lescarbault, render it very probable that there is a zone of planets or asteroids within the orbit of Mercury, so as to form a third faint ring encircling the sun. Leverrier has also shewn that the perturbation of Mars indicates the existence of a zone of meteorites whose diameter is nearly equal to that of the orbit of the earth. Such a zone Avould most naturally explain the phenomena of meteorites and their periodicity.
The next marked example of the concentric structure is furnished by comets. We have ah'cady shewn that this is one of their most striking features. In this case, we see the very formation of the strata or envelopes. They grow before our eyes, and afford a type of the structure of the more solid bodies of the solar system.
Most of the planets are so remote from us, or so near the sun, that we cannot speak with certainty of their envelopes. As far as our knowledge extends, the moon stands lowest, as she has no shell of any kind surrounding the solid ball. Mars probably comes next. We can at all times see the fixed features of his surface, and nothing like clouds has been detected, though there is evidence for an atmosphere. Next comes the earth, with her far-extending atmosphere and her stratum of clouds. Jupiter ranks next in order; and lastly, Saturn, the most complete example of concentricity of structure.
In the case of the moon, taken as a whole, we do not indeed find a concentric structure; but in a former chapter we shewed that almost the whole surface is covered with volcanic craters, the principal feature of which is concentricity. The cone in the centre — the encircling cavity—the rim, with its successive terraces, all combine to carry out the planetary ideal.
When we descend from the cosmical type of the planetary system to the lowest forms of organisation, we discover the same concentric feature. The section of a tree exhibits the concentric rings of the planet. The flower with its pistil in the centre, and its encircling anthers, petals, and calyx, shadows forth the all-pervading plan, alike stamped on the orb of heaven and the lily of the valley.
When we range beyond the solar system, and extend our view to other suns and systems, we shall find diversity, but nothing to destroy the unity of plan, or shake our belief that all is the product of one divine idea. When we fathom the depths of space, we discover similar forms. We behold the masses of stars grouped into rings, and sometimes exhibiting traces of stratification. But there is a higher form, into which increased telescopic power is fast resolving other forms, viz., the spiral. The planetary type is the concentric arrangement of the section of a tree. The streams of stars constituting nebulæ, are coiled up like the mainspring of a watch, or wheeling round to the centre of a vortex. The spiral is the archetype, and comprehends the concentric circles of the planetary systems. We may not be able to trace the transition, but no one can compare the rings of Saturn with the spiral of a nebula, without feeling that they are allied forms, though the link may not yet be detected.
Our dwelling-place is in a small corner of a vast edifice, and, roam where we may, we shall find proofs that the plan is the same throughout. The cathedral of Cologne, now drawing towards completion, has had many architects employed upon it, but there is, in every part, evidence of one presiding mind. The successors of the original designer have only striven to carry out his ideas. There is one pervading style in the architecture of the heavens, and though subordinate agencies have been employed to carry it out, they do not in the least prevent us from recognising the hand of the Original Designer. The materialist may say that the concentric structure, as well as all the beauty and harmony of the system, can be explained by certain great material laws. But, granting that these laws do exhibit the modus operandi do they, in the least, supersede the necessity of a planning and presiding mind? The style of the solar system is an embodied idea; and an idea is a thing of mind, not of matter. We do not get rid of the necessity of genius by shewing how the artist handles his brush, and lays on his paint. The paints and the brush are only the material vehicles by which the ideas of genius are transferred to the canvas. No more do the laws of matter supersede mind. They are only the media through which the ideas of the Divine Mind are transferred to the gallery of the universe. The simpler the means of the artist, the more marvellous are his achievements, and the simplicity and generality of the laws of matter, only enhance the marvels of the divine idea imprinted on the heavens. And what, after all, are the laws of matter but the mode in which the Divine Artist works? The mere description of the movements of a brush over the canvas, surely does not supersede the hand, and the mind that guides the hand, of the artist? We might as well suppose the chisel of itself sculpturing the Apollo Belvidere, as the laws of matter, of themselves, fashioning the hosts of heaven into such wondrous forms of order and beauty.