God's glory in the heavens/The Sun: Its Work And Structure
Section of the Sun.
VIII.
THE SUN: ITS WORK AND STRUCTURE.
John Kitto, before leaving for Cannstadt to lay his ashes in its quiet churchyard, was persuaded to have his likeness taken by the photographic process. Notwithstanding the sadness that weighed on his heart, he could not restrain the humour which so often served to buoy up his sinking spirits. He remarked to his daughter, while the photographer was adjusting the apparatus, that "the sun had hitherto lived like a gentleman, but that now lie was obliged to work for his living." But he was mistaken in thinking that the sun had ever the life of a gentleman. He has always worked as a slave, nay, he has been always the slave of slaves. He has really done all the work, while men and their machines have taken all the credit to themselves. They have only directed the work, while all the power has been supplied by the sun. We speak of the marvellous power of the steam-engine; but to what does it owe its power? The answer is, the elasticity of steam. But how is this elasticity accounted for? The answer is equally ready, that the heat of the furnace has produced it. But the circle of causation is not yet complete. From what source has the coal derived its heat? Till lately the answer would be held satisfactory, that the coal is fossil wood, and therefore it produces heat by burning. But we must now wring from nature the secret of this possession of heat and power by coal. The answer of science is, that the coal is merely a receptacle for the heat and light of the sun. The sun's energy is bottled up, as it were, in the coal, and the burning of it is the uncorking of the bottle. It may be said that this is only a play upon words, as it is a mere truism to hold that a tree could not grow without the influence of the sun, and that there could be no coal without trees; but that this does not imply that the heat of the coal is the very heat of the sun. Now, what we wish to impress is, that the identity is complete, and this results from the grand generalisation of recent times, that force, and heat is but a form of force, is indestructible, just as matter is indestructible. God has created a certain amount of force, as well as of matter, in the universe, and it is inconceivable that either should ever bo lessened in amount, except by a miraculous act of annihilation. This generalisation now looks like a truism j but how strano-e is it, that the human mind should arrive at it only in very recent times. But so it is in the whole history of human thought. The inscrutable mystery of one period is the self-evident axiom of another.
Another source of power of which we avail ourselves is the fall of water. We plant our mills on the banks of a stream, and the descent of the water turns the wheel. We do not readily think of the impalpable rays of the sun turning the spokes of the wheel; and yet the connexion is easily traced. The rays elevate the water in the form of vapour from one level to a higher; the vapour is deposited in the form of rain; the rain accumulates in the river; the river fills the buckets of the wheel, and through the operation of the wheel, the heat of the sun is converted into useful, industrial work; and this is done as really as if the rays turned round directly the spokes of the wheel.
It may be said that there is one kind of power at least which cannot possibly be traced to the sun—viz., animal power. The horse in harness, or the labourer with his spade, surely exercises a power that has no relation to the sun. Is not volition a power altogether distinct from material force? Does not the will create force? Science, however, clearly shews that this is no exception to the general rule. The body is to man what the coals are to the steam-engine. The mind may direct, but it cannot create. And every time that a man strikes a blow with a hammer, he as surely wastes a certain amount of physical force stored up in his body as every stroke of the piston in a steam-engine wastes a certain amount of coals in the furnace. The waste of tissues in the body corresponds to the combustion of coals in the furnace. But whence the power stored up in these tissues? The answer is, from the sun. All animal structures can be ultimately traced to vegetable food; and the vegetable world is only the storehouse of the force emanating from the sun. The only force existing on the face of the earth not traceable directly to the sun is that of the tides. The tides would exist if the fluidity of the ocean could be maintained, even though the heat of the sun was extinguished. The trade winds are also in part independent of the sun, the direction being due to the rotation of the earth. These, however, form but insignificant exceptions to the general rule, that the power available for the purposes of man can be traced to the sun as the great source.
The sun, then, is the great worker, and the slave of man. He works every spinning-jenny in our manufacturing towns, forges every shaft, propels every ship, turns every water-wheel, and moves the limbs of every man and animal. Man, with the power of intellect, merely stands over him with the rod of dominion, and directs his giant strength to suitable tasks. In one point of view, we may well exclaim, "What is man, that thou art mindful of him? or the son of man, that thou shouldst visit him?" But the above views give new force to the declaration, "Thou hast crowned him with glory and honour; thou madest him to have dominion over the works of thy hands: thou hast put all things under his feet."
The triumphs of mechanical genius are the boast of our age, as well as the foundation of much of our national wealth; but how rude are the inventions of men compared to the adjustments of the Divine Mechanician in the solar system! We place a furnace on the ground, and by means of a system of boilers, cylinder, piston, levers, shafts, and wheels, are enabled, in the topmost storey of a factory, to spin thread of gossamer fineness; and no intelligent person has ever witnessed the sight without being impressed with the marvellous dominion of man over the material world. But how puny, after all, is this effort compared to that which the working power of the sun exhibits! Here the furnace is not placed a few yards distant, but 95 millions of miles, and on what a stupendous scale! This world, compared to the sun, is no larger than a single stone of St Paul's compared to the whole fabric. It is one of the most difficult problems in practical mechanics to transmit power to a distance, and we have to employ the rude device of long shafts, as in factories; rope and drum, as in the case of railway inclines; or air-pumps, as in the case of atmospheric railways; and, after all, we can only act at a very limited distance. But the sun transmits its power many millions of miles without the aid of mechanical contrivances, and so smoothly and silently that we are almost unconscious of its working. It is by the impalpable lever of the sunbeam that the central power acts on our distant globe. And mark how conveniently concentrated the sunbeams are for our daily use. Were we under the necessity of relying upon the diffused heat of the sun, it would be very difficult to apply its power. We might, no doubt, employ glasses to condense the rays of the sun upon steam-boilers, but the result would be more curious than useful. We have, in nature, a far more useful condensation, viz., fuel, which is just a vehicle for the sun's power. The water-fall is another convenient form of condensed power supplied to oar hand. The sun's rays are imprisoned by the very act of raising the water to a higher level; or, in other words, they are transformed and condensed into mechanical power.
This wondrous mechanism, by which the power of the sun is transmitted to our globe, and conveniently stored up for man's use, is to us a far more striking illustration of divine intelligence, than the mechanism of the solar system by which its stability is maintained. The attention of theologians has been almost exclusively turned, since the days of Newton, towards this one point, as the grand proof of a presiding intelligence. But it may be questioned whether a divine intelligence might not as well be proved from the order of a system, one element of which was, that the present arrangement was not permanent, but only a cycle in some grander evolution. Were it proved, as some astronomers hold, that the solar system and the system of Saturn's rings are hastening to a dissolution, or rather fulfilling their rôle as parts of a grander scheme, would we be forced to abandon the whole as proving a divine intelligence? There may be as much beauty and order in a mutable as in a permanent system, and where these elements are found, we have proof of intelligence. The argument for intelligence rises to a higher species of proof, when we consider not merely the beautiful adaptation of one part of the material machine to another, but also the correlation of the machine to life and intellect Now, the most marvellous of such correlations are those which are furnished by the sun, as the grand moving power on the face of our globe, and a moving power in virtue of its light and heat. Gravitation is not properly a moving power. It is only a condition, not a source of power to man. No doubt, if we raise a stone it will fall by gravity to the earth, when we drop it from our hand; but the great want of man is a power to raise the weight, and what we mean by a moving power is just one that can raise a weight. Now, the sun, as the great central furnace of the machine, is the prime moving power of the world—the lifter of every weight. He drives the great shaft of the machine, and all that man does is merely to put on a belt upon the drum when he wishes to utilise the power.
Man's body may, no doubt, be regarded as a working machine, its power being derived, as that of all other machines, from the sun; but its chief function is, as the vehicle of intellect, to direct the illimitable power at his command. Man, valued simply as a source of mechanical power, is worth only three tons of coals. Let a man labour all the days of his life, and his labour will not exceed the mechanical power stored up in a single truck of fuel. Nothing can illustrate more strikingly the superiority of intellect, and afford a more convincing proof that the differentia of man is mind, and that his body is but an accident. It was needful, however, that his body should, to some extent, be a source of power to open the sluices of energy stored up in the material world around him. The engine-driver needs bodily strength to work the valves, and so direct the giant power that is to propel a floating palace across the ocean with the swiftness of a race-horse. Intellect thus enables man to multiply indefinitely the strength of his body.
Let us now turn to the structure of the vast furnace which supplies us with all our moving power. It is strange how little attention has been paid till recently to this function of the sun. The human mind seemed to be quite satisfied with the grand discovery of Newton, that the sun is the centre of gravitation in the solar system; and can we wonder that it should, for a time, be entranced with the discovery, so that still more interesting relations of the sun to man should be overlooked? The attention of physicists has now been fairly arrested by this subject, and much light has already been thrown on the constitution and structure of the sun.
Much of our ignorance of the constitution of the sun may be ascribed to the awe and mystery with which it has always been regarded. The oriental worshipper of the luminary would shrink from the idea of unravelling the mystery of the universe by too curious a scrutiny, and a similar feeling appears to have restrained the prying eye of the astronomer. The spell of mystery is now broken, and the sun must submit to examination like any of his subject planets.
It is almost incredible that there is no authentic account of observations of the spots on the sun till a very recent period. Millions of worshippers for ages hailed the rising sun, or bowed their faces at his setting; and yet these spots seem never to have been observed, though quite noticeable often by the naked eye. One would almost be inclined to conclude that they are a modern feature of the sun, were it not that we have many parallel cases, where obvious facts have been overlooked for successive generations. The experience of most people will corroborate this fact from their own experience. How few have actually seen a spot on the sun, though every person must have had many opportunities of observing them! There is no town so favourably circumstanced for the observation of the spots as Glasgow. The cloud of smoke that usually hangs over it, mingled with the fog of the river, affords an admirable darkening medium for viewing them with comfort. Yet how few of the inhabitants have seen them, though there are few days in winter which do not present favourable opportunities for noticing objects often so conspicuous to the naked eye.
It was probably the advantages of the murky atmosphere of Glasgow that led Dr Wilson, the discoverer of the nature of the spots, to direct his attention to the subject. His theory is now almost universally adopted, though the recent results of spectrum analysis will probably lead to some modification. The spots are perforations in the luminous envelope of the sun, through which we see its dark body. This envelope or photosphere may be conceived as a stratum of luminous cloud, floating in a transparent atmosphere. But when we look down through the perforation, we see the edges of other strata, apparently non-luminous. Two of these have been detected, and there may be many more. The sun may then be conceived of as composed of a dark central body, encompassed by successive envelopes or shells, suspended at different heights in the atmosphere—the uppermost being the one which forms the luminous disc of the sun. A Chinese ivory ball, composed of carved concentric shells, represents very well the structure of the sun and the nature of the spots. In looking down the large holes in the ivory ball, we see the successive edges of the concentric shells, and in like manner do we see the successive edges of the concentric strata of the sun. The visible portion of the middle stratum forms the penumbra or shading round the black centre, which is merely the dark body of the sun seen down through the perforation or funnel. But recently another gradation of shade has been discovered, indicating another stratum. The figure at the head of this article illustrates this. The outermost unshaded ring represents the luminous stratum, and the other two interior rings are the non-luminous strata, which may so shade the body of the sun as to fit it for the abode of living beings.
The late solar eclipse was looked forward to with intense interest, as likely to throw new light on the constitution of the sun, and it has not disappointed expectation. The two grand points to be determined were, the nature of the red flames, and that of the corona seen during the time of totality. In regard to the red flames, the observations of Leverrier, who conducted the expedition, are quite conclusive. He has established beyond all doubt that they belong to the sun. But not only so, he has shewm that the flames are only prominences in a red stratum, enveloping the whole luminous disc of the sun. Another concentric shell has thus been added to the sun. The light of this stratum is so comparatively faint, that it is quite invisible, except when the moon, in a total eclipse, intercepts the overpowering light of the white disc. When we look at the disc of the sun, we are looking through this rose-coloured stratum, but its colour is quite obliterated by the light of the stratum beneath. It has been supposed that the prominent flames correspond with the spots in the sun, as if they were caused by a gas rising up through the spots, as through a chimney from below. When we view the disc of the sun with a telescope, we find that it is strangely mottled with bright wavy lines, called faculæ and minute dark points throughout its whole structure. The appearance is very much that of a sponge. The corrugation of the surface of the sponge represents the wavy appearance of the disc, and its numerous pores, the dark points in question. The large spots, or maculæ, may be represented by the rugged perforations through the mass of the spoage. The rose-coloured stratum may be supposed to be produced by some gaseous substance pressing up through the structural pores of the photosphere, and the prominences rising above the general level have been regarded as the same gaseous product issuing in greater volume from the spots or perforations. The stratum of smoke hanging over a large manufacturing town presents an appearance similar to that of the rose-coloured stratum of the sun. The smoke issuing from the innumerable chimneys of private houses corresponds to the red substance issuing from the pores of the photosphere, and a uniform stratum is in this way produced. Above the general level are the tall chimneys of factories, vomiting forth their volumes of smoke, which is carried away by the wind, parallel to the murky stratum beneath. The shapes, however, of the red prominences give us rather the idea of tongues of flame than of volumes of smoke, and the red stratum looks like a sea of flame violently agitated by the wind. The section of the red stratum, seen in the total eclipse, and represented in our illustrative figure, suggests the idea of the line of fire presented by a burning forest in Canada, or a pine barren in Florida. As the tide of fire sweeps along, there is a general level, but the flame is broken up into distinct tongues and waves; and when it meets with some ancient and lofty clump of trees, it rushes up to the topmost point, and this burning spire towers far above the sea of fire beneath. In some places there may be a calm, and the tongues shoot straight up; at other places, the flames are agitated by a fierce tempest, and they are bent at right angles to their original direction. In other cases still, the gas does not take fire till it has attained a considerable height, and then the flame appears quite detached from the general surface. It will help us to conceive the scale of the conflagration if we keep in view that some of the single tongues of flame were, in the late eclipse, more than 300 times larger than the earth. The observations in connexion with the recent eclipse do not, however, confirm the supposition that the red prominences coincide with the spots of the sun. Leverrier has called in question the generally received theory of the spots of the sun. He reverts to the old hypothesis, that they are not perforations in the photosphere, but clouds floating in the atmosphere. This is, however, quite inconsistent with the facts of the case. The spectrum observations of Professors Bunsen and Kirchhoff rather countenance the idea that the photosphere is not a gaseous envelope, but the solid body of the sun itself,—the atmosphere in which the metals are found being supposed to be exterior to the photosphere. The phenomena of the spots are irreconcilable with this theory. The supposition that the faculæ are due to waves in the red stratum is more plausible.
Foucault was intrusted with the observations on the corona, or broad zone of light, extending far beyond the red stratum, and presenting very much the appearance of the glory around a saint's head. He has satisfied himself that the corona is not the atmosphere of either the sun or moon. He holds that it is not an objective substance at all, but merely an affection of light, due to the edge of the moon. When light passes the edge of opaque bodies, it is diffracted and bent into the shadow. Foucault holds that the corona is merely the diffracted light of the sun. The radial beams of light seen in the corona, he ascribes to prominences in the contour of the moon. This conclusion cannot be admitted. There is, on other grounds, every probability that there is an atmosphere in winch the various solar strata float, and we would have reason to expect that this atmosphere would be rendered visible in a total eclipse. Father Secchi declares, that he saw the corona for a few seconds after the disc of the sun appeared; and such a phenomenon is incompatible with the theory of diffraction. None of the observations have given any countenance to the idea, that the corona is the atmosphere of the moon. Mr Airey holds that the phenomenon would receive a satisfactory explanation dn the supposition that the earth's atmosphere extended to the moon. The corona, in that case, would be only a portion of the earth's atmosphere illuminated by the sun. The result of the observations of the late eclipse amounts to this, that the red prominences have been proved, beyond all doubt, to belong to the sun, and that they are mere elevations of a stratum of the same matter enveloping the whole solar sphere. The photographic observations of Mr Warren de la Rue are very conclusive. He took several views, with short intervals between, which clearly exhibit the progress of the moon across the red prominences. While those on the one side were gradually elongated, those on the opposite side were shortened. This clearly proves that they belong to the sun, and not to the moon, the probability being that they are only the faculæ seen in profile. Vulcan was anxiously looked for, but it was not detected.
When we look with curious eye into the glowing furnace of a steam-engine, we have to shade our face from the fierce glare, and survey the bars and boiler-tubes in detail. When we look into the great central furnace of the solar system, we need a screen too, and the moon admirably serves the purpose. It most effectually intercepts the light and heat of the central parts, so that we may descry the fainter objects round the circumference. Night reveals to us a new glory of the heavens, by unveiling its innumerable hosts, and the darkness of the eclipse has revealed to us a new glory of the sun. This strange structure is not an isolated case; it has a typical significance. It reveals to us the unity of plan of the great Architect. This concentricity of structure is probably the grand archetypal element of suns and planets. Saturn presents a curious modification—the concentric shells being reduced to concentric rings; and it is singular enough, that the red shell or firmament should be added to the sun, almost simultaneously with a dark ring to Saturn. We might have little difficulty in tracing indications of this concentric structure in the other planets, but we may not linger on this tempting field of speculation.
Having inspected the furnace, which is the grand source of power on the surface of the earth, the inquiry naturally suggests itself: How is this power sustained? How is the furnace kept burning? Formerly, there was a vague idea that the sun could dispense heat for evermore without ever wasting; but the law of the correlation of physical forces tells us, that while the sum of force in the universe is ever the same, any special form of force must waste by exercise unless it is replenished. The sun cannot give forth force without loss, unless it receives in turn. The favourite theory at the present moment is, that the sun is surrounded with a zone of fuel in the form of meteorites, and that it is supplied from this source as the furnace of a locomotive is fed from the tender which follows it. But whence comes this zone? How is the circle of correlation to be completed? Here we have reached the boundaries of knowledge, and even speculation is silent. We can trace only a few links of the chain of causation depending from the throne of the Eternal; the last link is hid in impenetrable mystery. "Lo, these are parts of his ways, but how little a portion is heard of him! but the thunder of his power who can understand?"