Ralph Allen Sampson

“ In consequence of the radiation of heat the whole body will be more condensed than before, but whether it is hotter or colder than before will depend on whether the contraction set up is more or less than enough to restore an exact balance. If we are dealing with comparatively recent periods there is no evidence of progressive change, but if we go to remote epochs and suppose the sun to have once been diffused in a nebulous state, it is clear that its shrinkage, in spite of radiation, has left it hotter, so that the shrinkage has outrun what would suffice to maintain its radiation. ”

“ Now under the law of attraction according to the inverse square of the distance, or any other inverse power beyond the first, the energy of even a single pair of material points is unlimited, if their possible closeness of approach to one another is unlimited. If the sources of energy within the atom can be drawn upon, and the phenomena of radio-activity leave no doubt about this, there is here an incalculable source of heat which takes the cogency out of any other calculation respecting the sources maintaining the sun’s radiation. ”

“ The radiation from a spot changes little as it approaches the sun’s limb; in fact Hale and Adams find that the absorption from the limb itself differs from that of the centre of the disk in a manner exactly resembling that from a spot, the same lines being strengthened or weakened in the same way, though in much less degree, with, however, one material exception: if a line is winged in the photosphere the wings are generally increased in the spot, but on the limb they are weakened or obliterated. ”

“ To understand the phenomena of the sun, we should reproduce them upon the earth; but this is clearly impossible since they take place at temperatures which volatilize all known substances. Hence our only guides are such general laws of mechanics and physics as we can hardly believe any circumstances will falsify. ”

“ The temperature gradient at the confines of the photosphere must certainly ascend sharply at first. When we say the sun's temperature is 6000°, of what level are we speaking? The fact is, that radiation is not a superficial phenomenon but a molar one, and Stefan's law, exact though it be, is not an ultimate theory but only a convenient halting-place, and the radiations of two bodies can only be compared by it when their surfaces are similar in a specific way. ”

“ It is equally clear that there is a point beyond which contraction cannot go, and thereafter, if not before, the body will begin to grow colder. There is thus a turning-point in the life of every star. The movement towards contraction and consequent rise of temperature which radiation sets up, like other motions, overruns the equilibrium point, only however by a minute amount ”

“ In the higher chromosphere on occasions metallic gases are carried up to such a level that without an eclipse a bright line spectrum of many elements may be seen, but it is always possible to see those of hydrogen and helium, and by opening the slit of the spectroscope so as to weaken still further the continuous spectrum from the photosphere (now a mere reflection) the actual forms of the gaseous structures called prominences round the sun’s rim may be seen. In the visual spectrum there are four hydrogen lines and one helium line in which the actual shapes may be examined. ”

“ The fall of meteoric matter into the sun must be a certain source of energy; if considerable, this external supply would retard the sun’s contraction and so increase its estimated age, but to bring about a reconciliation with geological theory, very nearly the whole amount must be thus supplied. It is easy to calculate that this would be produced by an annual fall of matter equal to one nineteen millionth of the sun’s mass, which would make an envelope eight metres thick, at the sun’s mean density ”

“ The name has no reference to the appearance of the body to the eye; when emitting energy, its radiations will be of all wave-lengths, and if intense enough will appeal to the eye as luminous between about wave-lengths 7600 and 4000 tenth-metres; this intensity is a question of temperature, and as it is exquisitely inappropriate to speak of the bulk of the solar radiations as black, the writer will speak instead of amorphous radiations from an ideal radiator. The ideal radiator is realized within any closed cavity, the walls of which are maintained at a definite temperature. ”

“ They have lost completely the gaseous characteristic of producing a line spectrum, and radiate like incandescent solids. The surface region which yields a continuous spectrum is called the photosphere; it possesses optically a sharp boundary, which is generally a perfect sphere, but shows occasionally at the rim slight depressions or more rarely elevations. Enclosing the photosphere is a truly gaseous envelope which is called the chromosphere, and which shows a spectrum of bright lines when we can isolate its emission from that of the photosphere. ”

“ The confines of the sun are visibly in a state of turmoil, for which sufficient cause can be assigned in the relative readiness with which the outer portions part with heat to space, and so condensing produce a state of static instability, so that the outer surface of the sun in place of being fixed is continually circulating, portions at high temperatures rising rapidly from the depths to positions where they will part rapidly with their heat, and then, whether perceived or not, descending again. ”

“ It is in fact an impossibility that; loss should go on without regeneration, for if any part of the sun’s body loses heat, it will be unable to support the pressure of neighbouring parts upon it; it will therefore be compressed, in a general sense towards the sun’s centre, the velocities of its molecules will rise, and its temperature will again tend upwards. ”

“ Stefan’s law of radiation according to the fourth power of the temperature is too difficult to pursue, but if we are content with cognate results we can follow them out mathematically in a hypothetical law of the first power. We then find that the density would increase as we go outwards, at first slowly, but finally with extreme rapidity, the last tenth of the radius comprising half the mass. The radiation from such a body would be practically nil, no matter how hot the centre was. ”

“ In the outer strata a different state must prevail. Rapidly falling temperature must (and visibly does) produce furious motions which wholly outrun mere restoration of statical balance. Portions change places so rapidly and so continually, that we may take it, where any average is reached, the energy is so distributed that there is neither gain nor loss when such a change occurs. ”

“ Apart then from absorption there will be a discontinuous change in brightness in the apparent disk at that value of the angular radius d which corresponds to tangential emission from the upper lever r ′ of this mirage-forming region. Of course we are unable to say whether such a region is an actuality in the sun, on the earth it is an exception and transient, but the greater the dimensions of the body the more probable is its occurrence. The theory can be put to a certain test by considering its implications with respect to colour. ”

“ The sun’s nearest neighbour, is α Centauri, which is separated from it by 270,000 times the earth’s distance, a space which it would take light four years to traverse. It is fairly certain that not more than six stars lie within twice this distance. No certain guide has been found to tell which stars are nearest to us; both brightness and large proper motion, though of course increased by proximity, are apparently without systematic average relation to parallax. ”

“ The body of the sun must consist of uncombined gases; at the surface the temperature is some 2000° C. above the boiling point of carbon, and a little way within the body it may probably exceed the critical point at which increase of pressure can produce the liquid state in any substance. ”

“ Its temperature must be dominated directly or indirectly by the surface radiation, and since the matter is gaseous and so open to redistribution, the same is true of density and pressure. It is true thatMechanical State Internally. within the body radiations must be stifled within a short distance of their source; none the less, they will determine a temperature gradient, falling from the centre to the borders, though for the most part falling very slowly, and we may ask what relative temperatures in different parts would maintain themselves if once established. ”

“ Though few follow him so far, an explanation Anomalous Dispersion. of the principle will make it clear that there are numerous possible opportunities for anomalous dispersion to qualify inferences from the spectrum. Theoretically anomalous dispersion is inseparable from absorption. When a system vibrating in a free period of its own encounters, say through the medium of an enveloping aether, a second system having a different free period, and sets it in vibration, the amplitude of the second vibration is inconsiderable, except when the periods approach equality. ”

“ The earth would intercept an amount of it proportional to the solid angle it subtends at the sun; that is to say, it would receive a deposit of meteoric matter about one-tenth of a millimetre of density say 2, over its whole surface in the course of the year, So far there is nothing impossible in the theory. ”

“ The sun is a small target for a meteorite coming from infinity to hit, and if this considerable quantity reaches its mark, a much greater amount will circulate round the sun in parabolas, and there is no evidence of it where it would certainly make itself felt, in perturbations of the planets. ”

“ These planets are more remote than Mars, but that loss is more than outweighed by the fact that they are indistinguishable in appearance from stars. The measures were made with the Cape heliometer and have never been superseded, for the latest results with the minor planet Eros exactly confirm Gill’s result—8.80′′—while they decidedly diminish the associated probable error. The planet Eros was discovered in 1899, and proved to have an orbit between the earth and Mars, while every one of the other five or six hundred known asteroids lies between Mars and Jupiter. ”

“ A second objection is that it fails in its purpose, because 20,000,000 years ago it would give a sun quite as much changed as the contraction theory gave. If we examine chemical sources for maintenance of the sun’s heat, combustion and other forms of combination are out of the question, because no combinations of different elements are, known to exist at a temperature of 6000°. A source which seems plausible, perhaps only because it is less easy to test, is rearrangement of the structure of the elements’ atoms. ”

“ Taking the value at 2.1 the earth is therefore receiving energy at the rate of 1.47 kilowatts per square metre, or 1.70 horse-power per square yard. The corresponding intensity at the sun's surface is 4.62 × 104 as great, or 6.79 × 104 kilowatts per square metre = 7.88 × 104 horse-power per square yard—enough to melt a thickness of 13.3 metres (=39.6 ft.) ”

“ This supposes the present density nearly uniform; if it is not uniform, any amount added to the former period is subtracted from the latter. A contraction of 0·2′′ or 90 m. in the sun’s radius would maintain the present emission for 3500 years. Such a rate of change would be quite insensible, and we can affirm that for recent times there is no reason to look for any other factor than contraction; but if we consider the remote past it is a different matter. We know nothing quantitatively of the radiations from a nebulous body ”

“ It is found that atmospheric absorption is generally greater in summer than in winter, a difference of 20% being found between March and August; morning hours show a rapid and often irregular increase of transparency, culminating shortly after noon, after which the diminution is slow and comparatively regular. ”

“ They are carried across the disk by the sun's rotation, partaking in the equatorial acceleration; they also show marked displacements of their own, whether with, or relative to, the neighbouring photosphere does not appear; at the beginning of their life they usually outrun the average daily rotation appropriate to their latitude. ”

“ Other information about the spots is given below, in connexion with their spectra. It may be said that nothing definite has been established as to what they are. The statement known as A. Wilson’s theory (1774) , that they are hollows in the photosphere, long supposed to be proved by perspective effects as the spot approached the limb, is discredited by F. Howlett’s careful drawings, which, however, do not establish the contrary. ”

“ Two other causes of displacement call for mention in their bearing on the solar spectrum—pressure and anomalous dispersion. The pressure which produces a continuous spectrum in gases at a temperature of 6000° must be very great. Recent experiments on arc spectra at pressures up to 100 atmospheres by W. J. Humphreys and by W. C. Duffield show several suggestive peculiarities, though Effect of Pressure on Spectral Lines. their bearing on solar phenomena is not yet determined. ”

“ A few of the lines show a double reversal, the dark absorption line being greatly increased in breadth and showing a bright emission line in its centre. The umbra of a spot is generally not tormented by rapid line-of-sight motions; where any motion has been found G. E. Hale and W. S. Adams make its direction downwards; but round the rim and on bridges the characteristic distortions due to eruptive prominences are often observed. There appears to be some connexion between prominences and spots ”