THE CONSTITUTION AND PHENOMENA OF THE SUN.
The various theories thus reviewed, while not sufficient in themselves to account for the facts of our own solar system, are fatally defective in another respect. While they aim to account for the sun’s light and heat, they all fail to consider the active medium of the solar light and heat in the sun itself. It is not simply a highly-heated central mass glowing in space. It is a vast orb surrounded by different envelopes of incandescent vapors or gases, and by far the most vast in volume, as well as in light and heat-radiating power, are the photosphere and its superincumbent chromosphere, composed almost entirely of free hydrogen gas in a state of intense incandescence. Whence comes this enormous mass of hydrogen? And how explain the entire absence of free hydrogen gas from our own atmosphere and its replacement by oxygen? There is a recent theory propounded by Mr. A. Mott, which is set forth in detail in Professor Ball’s “In the High Heavens,” and which endeavors to account for the remarkable absence of free hydrogen gas from the earth’s atmosphere, for, as the author states, “It is a singular fact that hydrogen in the free state is absent from our atmosphere.” The theory, in brief, is that the molecules of hydrogen gas have an average speed of about a mile a second,—which, however, is only one-seventh that required to shoot them off into space,—but that these molecules are continually changing their velocity, and may sometimes attain a speed of seven miles a second; the result is that “every now and then a molecule of hydrogen succeeds in bolting away from the earth altogether and escaping into open space.” During past ages the molecules of hydrogen would thus have gradually wiggled up through the air, and finally disappeared into outer darkness for good and all; and thus “the fact that there is at present no free hydrogen in the air over our heads may be accounted for.” Since the molecules of oxygen have only a velocity of a quarter mile a second, that unfortunate gas remains behind and is consumed.
The first difficulty with this theory is to explain how, if the hydrogen wiggled off in this unceremonious manner, it ever wiggled on. There is no objection to a gait of this rapidity, however; it is highly creditable, in fact; but we have a right to expect some degree of consistency in even so light-headed a body as hydrogen gas. The article quoted thus continues: “If the mass of the earth were very much larger than it is, then the velocities with which the molecules of hydrogen wend their way would never be sufficiently high to enable them to quit the earth altogether, and consequently we might in such a case expect to find our atmosphere largely charged with hydrogen.” It will be seen that, according to this theory, hydrogen is able to achieve a speed of seven miles per second under exceptional excitement, and that this molecular velocity is just enough, and no more than enough, to give it egress. We know that Jupiter’s mass is three hundred times as great as that of the earth, and the attraction of gravity is so powerful on the surface of that planet that, as the writer just quoted says, “Walking, or even standing, would involve the most fearful exertion, while rising from bed in the morning would be a difficult, indeed, probably, an impossible, process.” We also know that the atmosphere of this planet is laden with enormous clouds floating at various altitudes and with incessant movements. We are told that “the molecular speed of aqueous vapor averages only one-third of that attained by the molecules of hydrogen.” Of course, on the planet Jupiter, hydrogen would have no chance of escape at all: it would just have to stay and take it, like the rest of us. Jupiter must thus have an atmosphere like our own, except that it is “largely charged with hydrogen.” Of the clouds upon this planet, Professor Ball says, “In fact, the longer we look at Jupiter the more we become convinced that the surface of the planet is swathed with a mighty volume of clouds so dense and so impenetrable that our most powerful telescopes have never yet been able to pierce through them down to the solid surface of the planet.” With the densities, molecular velocities, and specific gravity of the oxygen, nitrogen, and the hydrogen, with which latter the atmosphere of Jupiter must be “largely charged,” as it is said, it is difficult to understand how such enormous clouds of aqueous vapors, themselves composed of oxygen, which is a very slow-footed gas, and hydrogen, could travel about with such facility; we ought to find them packed down like London fog, to say the least, upon the surface of that planet, with the supernatant gases all adrift overhead. Jupiter is a hot body; it has not yet cooled down; and if it is provided with volcanoes, such as its great red spot and the analogies of the earth and moon would suggest, we can tell pretty nearly what would have happened long ago with a Jovian atmosphere like ours; but “largely charged with hydrogen,” if we compare it with, say, an equal mass of dynamite touched off by a volcanic explosion; there would not have been enough of old Jupiter left to swear by, and what was left would not have had any atmosphere at all. On Mars, the same writer thinks the oxygen would still cling, like the fragrance of the rose, but that all the molecules of the fleet-footed and excitable hydrogen would long since have taken French leave, as it did from the earth; but at the moon, on account of its small size and mass, both gases would have gone off incontinently together. “It is now easy,” the author says, “to account for the absence of atmosphere from the moon …. Neither of the gases, oxygen or nitrogen, to say nothing of hydrogen, could possibly exist in the free state on a globe of the mass and dimensions of our satellite …. Indeed, the weight of every object on the moon would be reduced to the sixth part of that which the same object has on earth.” Nevertheless, it may be said that the moon has considerable weight, as weights go, but with a comet it is quite a different matter. “These bodies,” the author says, “demonstrate conclusively that the quantity of matter even in a comet is extremely small when compared with its bulk. The conclusion thus arrived at is confirmed by the fact that our efforts to obtain the weight of a comet have hitherto proved unsuccessful …. It has thus been demonstrated that, notwithstanding the stupendous bulk of a great comet, its mass must have been so inconsiderable as to have been insufficient to disturb even such unimportant members of the solar system as the satellites of Jupiter.” Now, here is a state of things; for the spectroscope shows that comets are fully provided with a large supply of hydrogen, enough and to spare for ornament, even, and of nitrogen also, while it is the abnormally fugacious oxygen which has, apparently, taken its departure. Of course, such facts demonstrate the untenability of the theory, which is, besides, in direct contradiction with the laws governing gaseous diffusion. Gases pass into each other with the same velocity as into a vacuum, and it is not to be imagined that the molecules of hydrogen could thus move individually off, unless forced upward by the pressure of some other gas, which the law of gaseous diffusion makes impossible. We should as readily expect to see a tumbler full of iron balls, into the interstices of which loose sand has been poured, manifest a similar phenomenon by the wiggling out of the less dense sand at the top of the glass. One might also ask whence, if this theory had any substantial basis, could come the enormous volumes of hydrogen gas in the atmosphere of a new or temporary star, in a few hours, or the changes manifested in the atmospheres of the variable stars. So, also, the nebular or any other hypothesis of creation would be impossible under this theory, as the heavier and less mobile gaseous elements would remain behind, or be condensed nearest the center of gravity of the aggregating nebula, while the more rapid gases would disappear outwardly, and in consequence the sun would be found to be composed of the heavier elements exclusively, and each of the planets, in turn, would consist of only one or two elements, in accordance with the more and more mobile character of their molecular movements, and the uniformity of chemical constitution between the sun and planets, as well as the fixed stars, would not be found to exist. The theory, in fact, is an example of the endeavor to explain an easily understood difficulty by a less easily understood impossibility.
None of the different theories even attempt to account for the prodigious volumes of hydrogen in the solar atmosphere, and without its presence the sun, so far as we know, would be almost an inert mass, considered as a source of energy for the supply of our planetary system. We know, of course, that meteors contain sometimes as much as six volumes of gases, largely composed of hydrogen, at our own atmospheric pressure. But the pressure at the sun’s surface is more than twenty-seven times that at the surface of the earth, and yet the volume of hydrogen there existing visibly is vaster beyond computation than any possible mass of meteoric material could supply. So, also, while it may be granted that condensation of volume must vastly raise the solar temperature, how could it produce the enormous masses of hydrogen, the lightest of all the elements, unless they have been temporarily occluded and finally thrown out from within, which is impossible? These vast volumes of hydrogen are to be considered first of all in any attempt whatever to solve the problem of the source and mode of solar energy.
Considering the phenomena presented within the limits of our own solar system alone, we find that the earth is one of a single family of planets, each of which very closely resembles it, and all of which circle, in slightly elliptical orbits, at various distances around the sun, their orbits occupying substantially the same plane, thus making our solar system a flat disk of space occupied by the sun as a center, with the planets and their satellites moving harmoniously around it. The planets differ from each other in size, mass, and temperature, but each is surrounded by an envelope of aqueous vapor, suspended in an atmosphere substantially like our own. Professor Proctor, in his “Light Science for Leisure Hours,” says of the planet Jupiter, “His real surface is always veiled by his dense and vapor-laden atmosphere. Saturn, Venus, and Mercury are similarly circumstanced.” Of Mars he says that it is “distinctly marked (in telescopes of sufficient power) with continents and oceans which are rarely concealed by vapors.” Now, whence comes this aqueous vapor surrounding all the planets? Whether received originally from the diffused nebular mass from which our solar system is supposed to have been condensed, or attracted by the force of gravity from interplanetary space, like the meteors which fall upon the earth’s surface, it is evident that interplanetary space must once have been pervaded with aqueous vapor, since the nebular mass from which our solar system was constituted must have occupied at least the space embraced within its largest planetary orbit, and doubtless much more; and if so, such aqueous vapor, and other vapors also, must still persist in space, just as the meteoric particles which so constantly manifest themselves in our atmosphere. If the planets had no common origin, the evidence is equally conclusive, since then this identical substance could only have been derived from a common source, which can only be interplanetary space. This also is in accordance with the laws of attraction, which would operate to gather and condense the rarefied aqueous vapor of space around the planetary masses in definite proportions. In his “Familiar Essays on Scientific Subjects,” Professor Proctor says, “In fact, we do thus recognize in the spectra of Mars, Venus, and other planets the presence of aqueous vapor in their atmosphere;” and in his “Mysteries of Time and Space” he says, “We may admit the possibility that the aqueous vapor and carbon compounds are present in stellar or interplanetary space.” But in addition to this aqueous vapor which surrounds the planetary bodies, we find free oxygen in vast quantities, and, with this, free nitrogen in mechanical admixture, and these together constitute the atmosphere we breathe, and which sustains organic life by a process of slow combustion. But we find no free hydrogen either in our own atmosphere or in that of other planets. Turning now to the sun, we find that it is surrounded by an atmosphere as well as the planets, but that this atmosphere is composed not of free oxygen, but of free hydrogen. In his article, “Oxygen in the Sun,” Professor Proctor says, “Fourteen only of the elements known to us, or less than a quarter of the total number, were thus found to be present in the sun’s constitution; and of these all were metals, if we regard hydrogen as metallic …. But most remarkable of all, and most perplexing, was the absence of all trace of oxygen and nitrogen, two gases which could not be supposed wanting in the substance of the great ruling center of the planetary system.” The researches of Dr. Draper indicated, however, that oxygen could be found in the sun; not in his external atmosphere but far down within his surface. Professor Proctor says, “Dr. Draper mentions that he has found no traces of oxygen above the photosphere.” Such free oxygen cannot be associated with the hydrogen, however, even if its presence be finally determined, but it may be due to the deoxidation of solid compounds precipitated upon the sun from space, and held at a temperature above that of disassociation, as hydrogen is sometimes generated at the surface of the earth.
The vast mass of the solar atmosphere is composed of hydrogen gas, with which are found commingled vapors of the various elements which enter into the sun’s constitution, and this solar atmosphere corresponds in proportion, speaking generally, with our own atmosphere, except that the volume of solar hydrogen is vastly greater than that of terrestrial oxygen, for the reason, as will be explained, that water contains two volumes of the former to one of the latter.
In Appleton’s Cyclopædia the sun is thus described, (article by Professors Langley and Proctor): “To sum up briefly the received hypotheses of the physical constitution of the sun: of its internal structure we know nothing, but we can infer, from the low density of the solar globe as a whole, that no considerable portion is solid or liquid. The regions we examine appear to consist of cloud layers at several levels floating in a complex atmosphere, in which probably most of the elements are known to us, and certainly many of them exist in the form of vapor. Outside this complex atmosphere extend envelopes of simpler constitution, though into them occasionally arise the vapors which ordinarily lie lower down. The sierra, for instance, consists in the main of glowing hydrogen gas and that gas, whatever it may be, which produces the line near the orange-yellow sodium lines. The prominence region may be regarded as simply the extension of the sierra.” Of these prominences, Professor Ball says, “The memorable discovery made by Janssen and Lockyer, independently, in 1868, showed that the prominences could be observed without the help of an eclipse, by the happy employment of the peculiar refrangibility of the rosy light which these prominences emit …. We can now obtain, not, as heretofore, merely isolated views of special prominences through the widely opened slit of the spectroscope, but we are furnished, after a couple of minutes’ exposure, with a complete photograph of the prominences surrounding the sun …. The incandescent region of the chromosphere from which these prominences arise is also recorded with accuracy.” Resuming our quotation from Appleton’s Cyclopædia: “The inner corona is still simpler than the sierra, so far as its gaseous constitution is concerned; but here meteoric and cometic matter appears, extending to the outer corona and to great distances beyond even the visible limits of the zodiacal. Returning to the photosphere, we find it subject to continual fluctuations, both from local causes of agitation and from the subjacent vapor acting by its elasticity to burst through it; the faculæ, which are found to be above the general level of the photosphere, are taken to be heapings up of the luminous matter like the crested surges of the sea. All the strata are subject to great movements, which sometimes have the character of uniform progression analogous to our trade-winds, and sometimes are violent, and resemble in their effects our tornadoes and whirlwinds. Eruptive action appears to operate from time to time with exceeding violence, but whether the enormous velocities of outrush are due to true explosive action (which would compel us to believe that the sun is enclosed by a liquid shell, so as to resemble a gigantic bubble) or to the uprising of lighter vapors from enormous depths, as heated currents rise in our own atmosphere, is not as yet certainly known.” The sierra, or chromosphere, is thus described in the same article: “The sierra presents four aspects: 1, smooth with defined outline; 2, smooth but with no defined outline; 3, fringed with filaments; and, 4, irregularly fringed with small flames. The prominences may be divided into three orders,—heaps, jets, and plumes. The heaped prominences need no special description. The jets … originate generally in rectilinear jets either vertical or oblique, very bright and very well defined. They rise to a great height, often to a height of at least eighty thousand miles, and occasionally to more than twice that; then bending back, fall again upon the sun like the jets of our fountains. Then they spread into figures resembling gigantic trees more or less rich in branches. Their luminosity is intense, insomuch that they can be seen through the light clouds into which the sierra breaks up. Their spectrum indicates the presence of many elements besides hydrogen. When they have reached a certain height they cease to grow, and become transformed into exceedingly bright masses, which eventually separate into fleecy clouds. The jet prominences last but a short time—rarely an hour, frequently but a few minutes,—and they are only to be seen in the neighborhood of the spots. Wherever there are jet prominences there also are faculæ. The plume prominences are distinguished from the jets in not being characterized by any signs of an eruptive origin. They often extend to an enormous height; they last longer than the jets, though subject to rapid changes of figure; and, lastly, they are distributed indifferently over the sun’s surface. It would seem that in the jets a part of the photosphere is lifted up, whereas in the case of plumes only the sierra is disturbed.” Of these eruptions Professor Ball says, “Vast masses of vapors are frequently expelled from the interior of the sun by convulsive throes with a speed of three hundred, four hundred, and sometimes nearly a thousand miles a second …. The spectroscope enables the observer actually to witness the ascent of these solar prominences.”
The corona, which extends beyond the chromosphere, has been determined by its continuous spectrum to be a vast envelope extending at least a million miles from the sun’s surface. “It cannot be a solar atmosphere,” Professor Proctor observes in his article on this subject, in his “Mysteries of Time and Space.”… “It will be seen, then, how inconceivably great the pressure exerted by a solar atmosphere some eight thousand times as deep as ours would necessarily be, let the nature of the gases composing it be what it may.”… “If a man could be placed on the solar surface, his own weight would crush him as effectually as though while on earth a weight of a couple of tons were heaped upon him …. Now, it happens that we know quite well that the pressure exerted by the real solar atmosphere, even close by the bright surface which forms the visible globe of the sun, is nothing like so great as it would be if the corona formed part of that atmosphere.” In the article “Sun,” in Appleton’s Cyclopædia, it is stated that “Mr. Arthur W. Wright, of Yale College, has succeeded in showing that this light (the zodiacal) is not emitted from incandescent gas, but reflected from particles or small bodies, and hence derived from the sun.”… “There is reason to believe that the true solar corona extends much farther (than a million miles), and that, in reality, the zodiacal light forms the outer part of the solar corona.” Proctor, again, in his article on the corona, says, “It would seem to follow that the corona is due to bodies of some sort travelling around the sun, and by their motion preserved either from falling towards him (in which case the corona would quickly disappear) or from producing any pressure upon his surface, as an atmosphere would.” In his article on “The Sun as a Perpetual Machine,” he says, “There is every reason for regarding the zodiacal as consisting in the main of meteorolithic masses, a sort of cosmical dust, rushing through interplanetary space with planetary velocities. To such matter, assuming, as we well may, that space really is occupied by attenuated vapors, … the luminosity of the zodiacal would be attributable to particles of dust emitting light reflected by the sun or by phosphorescence (this last may be seriously questioned). But there is another cause for luminosity of these particles which may deserve a passing consideration. Each particle would be electrified by gaseous friction in its acceleration, and its electric tension would be vastly increased in its forcible removal, in the same way as the fine dust of the desert has been observed by Werner Siemens to be in a state of high electrification on the apex of the Cheops Pyramid. Would not the zodiacal light also find explanation by slow electric discharges backward from the dust towards the sun?” It may be observed in passing that such electrical glow is much more prominently, and more likely to be, the result of induction than of friction. In the article “Sun,” previously quoted, Professor Young says, “There is surrounding the sun, beyond any further reasonable doubt, a mass of self-luminous gaseous matter, whose spectrum is characterized by the green line 1474 Kirchhoff. The precise extent of this it is hardly possible to consider as determined, but it must be many times the thickness of the red hydrogen portion of the sierra, perhaps, on an average, 8′ or 10′, with occasional horns of twice that height. It is not at all unlikely that it may even turn out to have no upper limit, but to extend from the sun indefinitely into space.” In the same article the sun’s apparent diameter is placed at about 32′, so that the thickness of the above gaseous envelope would be not less than one-fourth the sun’s diameter, or more than two hundred thousand miles. This coronal envelope, extending out from the solar body until gradually merged into the attenuated matter of space, has a light so feeble that it can only be clearly observed during total eclipse. Professor Ball (“In the High Heavens”) says, “The sunlight is so intense that if it be reduced sufficiently by any artifice, the coronal light also suffers so much abatement that, owing to its initial feebleness, it ceases altogether to be visible.” During the great eclipse of 1893 it was photographed, and of these photographs the same author says, “One of the most remarkable features in the structure of the corona is the presence of streamers or luminous rays extending from the north and south poles of the sun. These rays are generally more or less curved, and it is doubtful whether the phenomena they exhibit are not in some way a consequence of the rotation of the sun. This consideration is connected with the question as to how far the corona itself shares in that rotation of the sun with which astronomers are familiar. I should perhaps rather have said that rotation of the sun’s photosphere which, as the sun-spots prove, is accomplished once every twenty-five days. Even this shell of luminous matter does not revolve as a rigid mass would do. By some mysterious law the equatorial portions accomplish their revolution in a shorter period than is required by those zones of the photosphere which lie nearer the north and south poles of the luminary. As to how the parts of the sun which are interior to the photosphere may revolve, we are quite ignorant …. We have no means of knowing to what extent the corona shares in the rotation. It would seem certain that the lower parts which lie comparatively near the surface must be affected by the rapid rotation of the photosphere; but it is very far from certain that this rotation can be shared to any great extent by those parts of the corona which lie at a distance from the sun’s surface as great as the solar radius or diameter …. The corona presents a curious green line that seems to denote some invariable constituent of the sun’s outer atmosphere, but the element to which this green line owes its origin is wholly unknown.” The same author quotes from Dr. Huggins as follows: “It is interesting to read what Dr. Huggins has to tell us about the solar corona. The nature of this marvellous appendage to the sun is still a matter of uncertainty. There can, however, be no doubt that the corona consists of highly-attenuated matter driven outward from the sun by some repulsive force, and it is also clear that if this force be not electric, it must at least be something of a very kindred character …. So far as the spectrum of the corona is concerned, we may summarize what is known in the words of Dr. Huggins: ‘The green coronal line has no known representative in terrestrial substances, nor has Schuster been able to recognize any of our elements in the other lines of the corona.’ ” The account given by General Myer—quoted in Professor Proctor’s article, “The Sun’s Corona”—of the great eclipse of 1869, as viewed from an altitude of five thousand five hundred feet above sea-level, is as follows: “As a centre stood the full and intensely black disk of the moon, surrounded by an aureola of soft bright light, through which shot out, as if from the circumference of the moon, straight, massive silvery rays, seeming distinct and separate from each other, to a distance of two or three diameters of the lunar disk; the whole spectacle showing as upon a background of diffused rose-colored light. The silvery rays were longest and most prominent at four points of the circumference, … apparently equidistant from each other. There was no motion of the rays: they seemed concentric.” Three diameters would make these rays extend two and a half million miles at least from the sun’s photosphere, or even its chromosphere. The coincidence between these rays and those observed (see above) in the eclipse of 1893 must be noted, since these latter were conceived at one time to be meteor streams. As those seen in 1893 radiated from the poles, and were curved in form, while those last noted radiated at four equidistant points, none polar, and were straight, it will be seen that, if both phenomena were of the same class, they could not have been due to meteor streams.
A typical sun-spot. (From the Popular Science Monthly, 1885.)