QB 52.1 C 3 THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID HUMBOLDT LIBRARY, [No. 49. Supplied to the Trade. R KTI.:KNARI.K, /^ //*< A'V?t/.f O;w/ w/V.v THE SUN: ITS CONSTITUTION; ITS PHENOMENA; ITS CONDITION BY NATHAN T. CARR, LL.D., JUDGE OF THE NINTH JUDICIAL CIRCUIT OF INDIANA. Covers for the LIBRARY, to hold firmly any number of copies from one to twelve Price, 60 Cents ; to Subscribers, 35 Cents. J. FITZGERALD, PUBLISHER, 20 LAFAYETTE PLACE, NEW YORK. PRIVATE LIBRARY OF CHARLES A. KOFOID. Cost. . VOLUMES OF THE HUMBOLDT LIBRARY, I. Containing the first twelve numbers. Octavo, cloth. Price, free by mail, $1.75. III. Containing the third twelve numbers. (25-36.) Price, free by mail, #1.75. IV. Containing the fourth twelve numbers. (37-48.) Price, free by mail, $1.75. Vol. II, containing the second twelve numbers. (13-24) will be ready soon. SPECIAL NOTICE. The abore-named bound volumes arc sold by IMF PIBI ISHKR ONLY. 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HUMBOLDT LIBRARY?! 5 POPULAR SCIENCE LITERATURE, No. 49.] NEW YORK : J. FITZGERALD. [FIFTEEN CENTS. October, 1883. Entered at the New York Post-Office as Second-Class Matter. $i 50 per Year, (12 Numbers). THE SUN: Its Constitution; Its Phenomena; Its Condition. BY NATHAN T.\ARR, LL.D., OF THE NINTH JUDICIAL CIRCUIT OF INDIANA. WITH AN APPENDIX. COPYRIGHT, 1883, BY N. T. CARR. PREFACE. The treatise here presented was not originally designed for publication in this form, but as a chapter in a more extended work on the "Evolution of Worlds," now in preparation. Its present publication, as a separate es- say, is by request, to which the author has given his assent the more readily as he hopes that his views upon the important subject here discussed, be- ing presented to the public now, may win for the main work, when it shall be completed, easier access to the minds of intelligent readers. The purpose has been so to treat the subject that the essay can be un- derstood by readers who may know nothing of the technical terms used in a scientific study of the Sun, and who know but little of even the most elementary facts developed by those who have pursued that study ; yet it is hoped that, modest as are the pre tensions of this little work, it will not be deemed even by the scientist to be unworthy of his attention. The forces and laws of matter, as known to us here on the earth, are made the basis upon which every pos- tulate and conclusion are made to rest, and all speculations not actually com- pelled by our knowledge of these laws are strictly avoided. Attraction is recognized as the primary cause of every feature observed in the Sun, producing the exterior crust (photo- sphere) by concentration, and by con- tinuance the interior heat, from whose repulsive or expansive force come the interior gas^s, eruptions, sun-spots and chromosphere. While it was impracticable to con- fute in detail each of the erroneous theories which have been advanced concerning the Sun, yet it is believed that the exposition here offered of its constitution, condition and phenom- ena affords a criterion of the scientific value of all such theories. N. T. C. COLUMBUS, Ind., Sept. 20, 1883. THE SUN; ITS CONSTITUTION, ETC. 1. PURPOSE OF THIS ESSAY DIFFI- CULTIES OF THE SUBJECT. So much has been written by learned physicists concerning the central luminary, that any further discussion of the subject, save upon the basis of new~ researches, might appear either rash or useless. Yet, those who have written are in such irreconcilable conflict in the deduc- tions which they have drawn from observed facts ; while the results of their labors are in so many instances presented to us in comparatively brief essays, or special lectures, the sole purposes of which have been to elucidate some limited feature, or elaborate some particular theory, that a hope of reconciling inconsistencies, or of presenting the subject so as to embrace all that is substantially val- uable contained in the many essays and lectures, may be reasonably en- tertained. If, however, in pursuing these mod- est purposes it appear to be necessa- ry, at times, to advance a new thought, recall a forgotten fact, or even pro- pound a new hypothesis; these thoughts, facts and hypotheses must be estimated according as they may be shown to harmonize with physical facts and natural laws. The subject will be treated as if nothing had before been written upon it, in the hope of being thus better understood. While this method will necessitate the repetition of much which is so well known as to need no such reiteration, yet the close asso- ciation of facts well known with those less known may cause the latter to be more clearly apprehended. Indeed, such facts as are universally recog- nized as truths may serve as valuable postulates in the demonstration of indispensable hypotheses, and should, therefore, accompany the enunciation of the main proposition. It should be borne in mind, on the \ery threshold of this task, that se- rious obstacles to the acquisition of a direct aud accurate knowledge of the subject confront us at every point. Among these, although not the most serious, is the refractive power of the Earth's atmosphere, which, while it apparently displaces the Sun, some- times to a distance equal to its own diameter, thirty -three minutes (33'), may, and undoubtedly does, distort in like manner, though in less degree, the relative positions and forms of the details upon its surface. An obstacle still more serious is the undulatory and absorptive properties characteristic of the Sun's own sur- roundings; for, while the former lends an apparent, and, it may be, real unsteadiness to the object looked upon, the latter alters or changes the light which comes to us, and causes it to produce upon our admeasuring aud testing instruments results, the significance of which is yet unknown. More fatal still to an accurate knowl- edge is the immense distance at which the object must be examined, and the limited powers of the aiding instru- ments which man has, as yet, been enabled to bring to his assistance. Under such circumstances it is not astonishing that our knowledge of the Sun should be in such a state of un- certainty as must be disheartening to all, save those who, fully reali/ingthe magnitude of the many obstacles to be overcome, entertain feelings of the highest satisfaction that so much has been learned, although that much is at the best but little. 2. DISTANCE FROM EARTH TO SUN. The question which first demands our consideration is that of the dist- ance of the Sun from us. The laws of gravitation and the principles of geometry suggest to us several methods for measuring this distance; but, upon trial, each of them; whether because of disturbing elements whose values can only be approximated, or because of unascer tained details appertaining to the heavenly bodies, produce variant re- sults in all final calculations. The third law of Kepler, that the square* THE SUN? ITS CONSTITUTION, ETC. 3 of the times of orbital revolution are as the cubes of the distance from the Sun, gives us only the relation of units of different denominations time and distance without giving the value of these relations ; and hence the paral- laxes must be relied upon as the only means of obtaining this desired in- formation. Yet here the as yet unknown value of the orbital movement of the Earth, in miles, which is at the base of these calculations, and can be approximated only, will render any calculation un certain ; and different calculations will be variant in proportion to the variations of the approximation made. A number of years ago, a parallax was determined from the planet Mars, and with the approximations then made an angle of 8. "96 (eight seconds and ninety-six hundredths) was re- solved upon, which would make the distance of the Sun nearly 96,000,000 miles. A parallax determined at the transit of Venus in 1 869 was estimated to distend an angle of 8."58, making the distance 95,300,000 miles. Ob- servations of the transit of Yenus in 1874 are calculated to give a distance of 93,300,000 miles. These calculations, however, by no means establish the actual distance of the Sun. Eminent English astron- omers, Proctor arid Lockyer among others, from the same sources of ob- servation make different approxima- tions, and arrive at quite different conclusions. One of these gentlemen makes the distance 92,500,000 and the other 91,430,000 miles. Thus a difference of little less than five millions of miles in the computed distance to the Sun enters into our con- siderations of that body, with no data existing by the aid of which the dis- crepancies can be removed or the un- certainties eliminated. The best American authorities upon this subject have agreed upon 92,- 750,000 miles as the most probable distance; and this being most in har- mony with calculations made upon the basis of the supposed velocity of light, is the most satisfactory; and it may be considered as sufficiently deter- mined, for the purposes of this discus- sion, that the Sun is distant from us 92,750,000 miles. 8. THE DIAMETER OP THE SUN. Logically, the next point to be as^ certained is the dimensions of that body. Here, again, equal uncertain- ties confront us. Since the micro- meter and the heliometer have been brought into universal and successful use, little difficulty is experienced in agreeing upon the angles which its disk distends; but the uncertainty upon this subject lies in determining which of the many angles distended by it at different periods of time shall be accepted as its real and true di- ameter. Owing to the eccentricity of the Earth's orbit, there are periods when the Earth, at perihelion, is at least 3,070,538 miles nearer the Sun than when farthest away, at aphelion. The greater the distance, the smaller will appear the Sun's disk, not only to the naked eye, but to every measuring in- strument which may be applied as well. Therefore, when the Earth is at perihelion, the disk of the Sun distends an angle of 32' 36", while when at aphelion it distends an angle of only 31' 32". Owing to the many irregu- larities in the orbit of the Earth, pro- duced by the perturbations, the mean of these angles can only be approxi- mated. Some astronomers take 32' 3" as the mean angle, and, assuming 95,300,000 miles as the distance to the Sun it is the distance which de- termines the values of these angles make the diameter of the Sun 888,812 miles. Most European authors, how- ever, adopt the lower mean angle of 32' even, and, taking 91,430,200 miles as the distance, make its disk only 852,584 miles in diameter. Most of our American astronomers also adopt 32' as the angle ; but, tak- ing 92,750,000 miles as the distance, they arrive at the conclusion that its diameter is 860,000 miles. THE SUN; ITS CONSTITUTION, ETC. Here we have discrepancies ranging over a difference of 36,000 miles in the diameter of the Sun. What con- clusions may be reached from the many careful observations made dur- ing the transit of Venus on the 6th of December, 1882, cannot now be anticipated. In the mean time, how- ever, let the diameter of the Sun be regarded as 860,000 miles. 4. THE FORM OF THE SUN. The feature next in order for con- sideration is the form of that body. When rising or setting, and still close to the horizon, the disk, to the naked eye, appears larger at its horizontal than at its perpendicular diameter. At any marked distance from the hori- zon, however, this appearance van- ishes: the disk presents a perfect ircle, and we are led to conclude that the horizontal appearance was but an optical illusion, occasioned by the re- fraction of our own atmosphere. When subjected to the most careful admeasurements by the heliometer, no differences in the diameters are de- tected; this fact impels to the conclu- sion that the disk is bounded by a per- fect circle. Upon the supposition, however, that the Sun is a rotating globe, our knowledge of the effects of centrifugal force would lead us to con- clude that in fact it had been oblated at the poles, and therefore, that it is at least slightly spheroidal in form. Yet if this feature exists, the oblate- ness cannot possibly exceed ^ parts of the equatorial diameter, a quantity so small as to be rendered impercepti- ble by the intense luminosity of the Sun's surface. Although to the unaided eye the Sun presents the appearance of a flat, circular disk, yet when carefully ex- amined through a powerful telescope, slight indications of a spherical form are observed. Faint, indeed the very faintest possible degradation of light near its limb may be observed. True, the evidence thus obtained would not, perhaps, by itself justify a conclusion of its rotundity ; yet it would be strongly suggestive of thi? fact, and prepare the mind to apply evidence of the same tendency more readily in this direction. Upon ap- plying the thermopile to the exami- nation, further evidence of rotundity is secured in the disclosure of the fact that the heat rays from the center which in the case of rotundity would be most direct are more :. tense than those from near the margins and re- moved from the center, which in the case of rotundity would also be more indirect. Convincing proof of its rotundity lies in the indubitable fact that it rotates on an axis. 5. ROTARY MOTION OF THE SUN. As has just been said, the Sun ie not a fixed and immovable body. On the contrary, it is known to revolve, or spin round on an axis. Proof of this is found in the observation of spots seen upon its surface, which ap- pear first on the eastern side of the disk, and move with a regular motion toward the western side: there they disappear, to reappear after the lapse of a comparatively regular period of time on the eastern limb again, and so on, repeating the same circuit. Of course this motion of the spots can be but seeming ; and the appear- ance must be produced by the actual movement of the Sun in an opposite direction. Hence, the facts which assure us of the rotary motion also inform us that this motion is from west to east. While these spots furnish satisfac- tory evidence of the rotation, in a general way, the proof presented by them is not yet understood to be so satisfactory as to the actual period of time occupied by the Sun in making a complete rotation. From an obser- vation of these spots made by a Scotch astronomer, Prof. Carrington, in 1863, he concluded that the time was 24 days, 23 hours and 19 minutes. Prof. Schwabe, in 1865, from similar observations made the time 25 days and five hours. In 1868 Pro'f. Sporer arrived at the conclusion that THE SUN; ITS CONSTITUTION, ETC. it waa 25 days, 5 hours and 37 min- utes. Later still, in 1871, Prof. Hornstein calculated it to be 25 days and 13 hours. Thus it is seen that even here we are confronted with perplexing uncertainties. In this instance the diversities arise from the fact of these spots not being stable or fixed upon the surface of the Sun, but having certain motions which are irregular, and others which are supposed to be separate; and they have therefore afforded to the observ- er no standard of time. The duration of the spots is uncer- tain, appearing and disappearing at widely different periods of time. One selected for observation may vanish under the eye of the examiner, and his labor upon that spot be lost. But other spots have been known to endure for quite long periods in one instance for nine months. If for such a period the locality of the spot upon the sur- face should remain the same, it would afford sufficient foundation for a satis- factory deduction. But it having been further observed by Prof. Carrington that spots on or near the equator move more rapidly than spots away from it on any of the latitudes or parts of latitudes, some astronomers have con- cluded that each zone of spots, so to speak, from the equator toward the poles, revolves in a different period of time, and that, therefore, this self- movement of their own affords no re- liable evidence of the time in which the sun makes a revolution. The dif- ference in the velocity of the move- ment of these spots is said to be such that, while a spot on the equator is making a circuit in twenty-five days, a spot at 30 latitude makes one in twenty-six and a-half days. As will be seen hereafter, the calcu- lations based upon this fact are mis- leading, and should have been elimi- nated from the elements upon which the results are reached. 6. PERTURBATING MOVEMENT. Besides the rotary motion just de- scribed, the Sun has another move- ment, which, although not important in results, should, however, not be overlooked. It is known that all the planets of the solar system revolve in orbits round the Sun in different pe- riods of time. Speaking in round numbers only, Uranus makes nearly two revolutions to one for Neptune, Saturn nearly three to one for Uranus, Jupiter about two and a-half to one for Saturn, Mars seven to one for Ju- piter, Earth nearly two to one for Mars, Venus one and a-half to one for Earth, and Mercury more than two and a-half to one for Venus. It is there- fore apparent that times may arrive when several, if, indeed, not all of these planets may be so nearly in conjunc- tion as to be on one side of the sun. In the event of such a concurrence, the combined attraction of these sev- eral bodies will suffice to draw the Sun toward them for a distance quite equal to one-half its disk or diameter. As the planets move on from this point of conjunction, their differing velocities and orbits cause them to separate ; and as they become more equally distributed around the Sun, that body vibrates back to its original locality. This translation or pertur* bation of the Sun is a movement seL dom mentioned in works on astron- omy, yet it is one which the unerring laws of gravitation compel us to recog- nize as a physical fact, and our knowl- edge of that body would be incom- plete in the absence of this evident truth. 7. THE SUN'S ORBITAL MOVEMENT. The Sun has still another move- ment which, while it in no wise affects its present condition, is yet of vast importance with respect to the past history and future destiny of that body, and all its attendant satellites as well. Long continued observation of the starry heavens has caused the beholder to suppose the bright gems which besprinkle the firmament to be in motion. More minute examination proves this motion to be apparent only, accounted for by either the axial or the orbital motion of the THE SUN; ITS CONSTITUTION, ETC. Earth 5 yet at the same time we learn that there is also a movement among the stars which cannot be ac- counted for upon the hypothesis of these motions of the Earth. Es- pecially is this true of such of the stars as seem to move continually along great circles, which as yet have never been known to return into themselves. Herschel by the aid of his, then, magnificent teles- cope, discovered that in portions of tlie heavens the stars seemed to be growing less dense, while in opposite portions they were growing more crowded, and that all appeared to move in one general direction, not- withstanding their own apparent in- ternal motions. This general move- ment appeared to be from the Con- stellation Hercules, and toward the Constellation Argo on the opposite side of the celestial sphere. Assum- ing this movement to be apparent only in the stars, and not susceptible of being accounted for by either of the two motions of the Earth which have been named, it must follow that this appearance is produced by some other movement of the Earth which is in a direction diametrically oppo- site. As the Earth has no third movement, unless it be one common to all the bodies of the system to which it belongs, and inappreciable, for this reason, it must be concluded that this appearance of the stars is produced by a contrary movement of the entire Solar System. In such an event the Sun would be moving to- ward the Constellation of Hercules, carrying with it, of course, all its at- tendant bodies. Argelander, Struve, Dunkin, and other astronomers since Herschel's time, have carefully surveyed this field of inquiry, and arrived at con- clusions strikingly confirmatory of the views held by that Nestor of the science. Since then, also, the spec- troscope has been brought into ser- vice, and it reveals more clearly the same fact. Not only does this new worker in the great field of nature confirm the fact of this movement of the Sun and its children through space, but it also teaches us that it is moving in that direction at the rate of four rniles per second of time. From the fact that the Sun and its system of planets seem moving to- ward a given point in the distant heavens, it should not be inferred that it is therefore moving in a straight iine. On the contrary, this movement must be supposed to con- form to the forward movement of all other heavenly bodies, which in every instance is curvilinear. From this species of evidence it is indeed more than merely probable that the Sun revolves about the center of gravity of the group of stars mentioned, of which it is a member, this center of gravity being situate nearly in the plane of the Milky Way, perhaps not distant from the star Rho Herculis to exceed ninety degrees. 8. THE SUN'S ATTRACTIVE FORCE DENSITY OF THE SOLAR MASS. From what has been said it will be learned that in diameter the Sun is quite 109 times greater than the Earth, and exceeds it in the mass of matter contained 355,000 times, and in the volume of space which the matter occupies 1,400,000 times. These facts being taken in connection with the power of its attraction as mani- fested upon other heavenly bodies, it is estimated that the attractive power of that body is but 27 times in excess of the Earth's attractive force. The matter of the Sun is in density but one-fourth that of the Earth, while it is 1.44 times greater than water. Using these results, it is computed that the Sun contains 360 quintillions of cubic miles of matter, and that it weighs two octillions of tons. It is further estimated that the light of the Sun, while 450,000 times greater than that reflected by our moon, is yet one hundred times less than the light emitted by the brilliant star Sirius. The estimated heat of the Sun will be considered later. THE SUN; ITS CONSTITUTION, ETC. 9. THE STJN'S ATMOSPHERE. When looked upon with the naked eye, the Sun appears as a huge ball of flaming fire ; but farther than this the eye teaches us nothing. With the aid of a telescope, however, many features of the body and its surroundings are developed which would have never been anticipated. Indeed, this vastly multiplied eye also discloses many things of which it gives no knowledge beyond the naked fact of their exist- ence, and of whose details man would have remained entirely ignorant had not the spectroscope, photograph, thermopile, and other assisting in- struments and processes been discov- ered and applied. While these searches after hidden truths bring us much valuable in- formation, yet all combined form but inadequate means of ascertaining the nature and constitution of the Sun. By their aid, however, we learn that the body itself is undoubtedly en- veloped by what may be called in a general way an atmosphere, which extends out beyond its periphery in all directions for a distance of 200,000 or even 300,000 miles. On approach- ing the sun we first encounter an at- mosphere, which is inappreciable on account of its rarity and the immense distance at which it is viewed. All along our path is found the omni- present interstellar ether ; but as we approach closer a point is reached where some other light and quite im- ponderable gas is mingled with the ether. If the ether be not nitrogen, then nitrogen, which, of all the gases, is least subject to the force of attrac- tion, and hence is the least massed around attracting bodies, will be first found mingled with it. At another stage of progress to the Sun, unques tionably oxygen next to nitrogen in the smah degree of attractive force will be found mingled with these, at first rarely, but increasing in quantity with the approach At still another step on our advance evidences of luminosity in the sur- rounding atmosphere may be detected. During a total eclipse of the Sun by the Moon, and while the intense light of the luminary is shutout from di- ect view, slightly luminous rays are seen mingled with the surroundings which we have described. At first, only mere points of the luminous matter present themselves, but as the Sun is neared, they grow broader, until at their base, so to speak, they are mingled with a mass of luminous matter, entirely pervading the space and surrounding the Sun, in a form which in its general aspects may be said to be spherical. At times, these projections are seen to extend out- ward beyond the mass of the lumin- ous surrounding for distances ranging" from one to two hundred thousand miles. These rays or projections are pinkish in color, and are not in- variably in the direct line of the radii of the Sun, but at different places and times have now a tan- gential direction; again, a curved one. Whether the atmosphere proper, into which they are projected, is in motion, as is sometimes our own, whether it serves as an irregular re- tarding medium, or whether both these conditions combine to produce these features cannot be satisfactorily settled. While this luminosity was first discovered during an eclipse of the Sun, yet later, both Janssen of Paris, and Lockyer of London, were enabled to detect its presence at any time when our own atmosphere was quiet, by the aid of the spectroscope. These protuberances have been sub- jected to spectroscopic analysis, but without entirely conclusive results. These efforts, however, disclose a faint continuous spectrum, in which the dark lines of the solar spectrum are discernible, indicating a reflected sun- light. This evidence also assures us that they are in part, at least, com- posed of gases, which, while lumin- ous, are not in such a highly heated state as to be self-luminous. The dark lines of the spectrum teach us that the light, before reaching our at- THE SUN; ITS CONSTITUTION, ETC. mosphere, passes through or among incandescent gases which have culled out some of the light vibrations of the body emitting them. This spec- trum is, therefore, silent but impres- sive proof that the projections are, indeed, thrown out into a gaseous at- mosphere not wholly unlike our own. Lockyer unhesitatingly pronounces other portions of this spectrum to be dncontestible evidence of burning or glowing hydrogen a substance which, as all physical astronomers ad- mit, predominates in the mass of lu- minous matter nearer the Sun Prof. Young also holds these projections to be hydrogen flames. There is still another feature of this spectrum which must not be for- 'gotten. It is a single bright line in the green portion, which has not been identified as the spectrum of any known substance. Whether this in- dicates the presence of some substance not yet known and named, or of some known substance placed in a condi- tion unknown to us is uncertain, as man is as yet learning only the alpha Jbet of the langauge of the spectrum. Unfortunately, nearly all authors treat of these projections as if they 'were poi tions of matter distinct and different from that found nearer or farther from the Sun. They are given a name Corona which is calculated to confuse, if not actually mislead ; but it should ever be borne in mind that they are but portions of the more interior surroundings of the Sun projected through this atmospheric surrounding by some force within or beneath it Mr. Lockyer, the eminent English spectro scopist, with the hope of making the subject clear to all, says the Sun is immediately surrounded by an atmos- phere composed principally of hydro- gen gas, portions of which are here and there thrown out beyond the general mass in the form of enormous hydrogen flames. 10. THE CHROMOSPHERE. As has just been incidentally men- tioned, after another stage of advance upon the Sun, following inward on the line of these projections, we find that the luminous matter first observed in distinct parts, has become general throughout the space surrounding the body, and that this entire stratum of atmosphere is ren- dered luminous. The region of space between the point where the luminos- ity becomes general and the surface of the Sun, from the fact of its pos- sessing color (chrome), is named the Chromosphere. This portion of the Sun's covering is variously estimated, at from one to two hundred thousand rniles in depth, not accurately uniform in shape, but growing constantly more dense as the Sun is approached. With the telescope no differences are observed between the Corona- projections, and the Chromosphere, save in the mere form. Within this chromosphere, as a pirt of it, may be seen by the telescope during eclipses, or detected by the spectroscope at almost any time, projecting outward- ly from the surface of the Sun, cer- tain prominences, distinguishable in color, density, and intensity, from the general mass of luminous matter in which they appear. When seen they are invariably noticed to be at, or near the equatorial regions of the Sun, and always in the line of the projections which have been named the Corona. Mr. Swift, who ob served the eclipse of 1878 from Capi- tol Hill, Denver, saw two of these prominences, which he describes as be- ing near the chromospherical crescent (from the drawing accompanying his description, it must be understood that he means by this, the edge of the Chromosphere nearest the Sun) pos- sessing the same general tint a bright pink located each in the line of immense projections beyond the Chromosphere. Their spectrum con- sists chiefly of bright lines on a dark ground, several of which are coinci- dent with the known lines of glow- ing hydrogen. A spectrum analysis THE SUN; ITS CONSTITUTION, ETC. of the entire Chromosphere, shows us that its outer portion is largely hydrogen, while in the portions nearer the Sun, iron, magnesium, oxygen, nickel, sodium, and many other sub- stances known to us, are discovered. Thus their spectra compel us to con elude, that these prominences are of the same nature and character as the surrounding Chromosphere. 11. OOBONA, PROMINENCES, AND FACULJE. A critical review of all that has been learned of these so-called prom- inences, leaves no reasonable doubt that they differ in no respect, except in extent, from the phenomena which have long been observed on the mar- gins of many solar spots, and given the name of faculae. On the edges of some of these spots are seen ele- vated ridges of a lighter color, and brighter than the general surface of the Sun. As early as 1859, the En- glish astronomer, Dawes, proved by observation that when viewed obliquely, as at the limb of the Sun, these faculas rose in elevated ridges far above the general level. In 1862, Prof. Hewlett observed an appear- ance which renders the connection between the faculse and these promi- nences quite certain . Just as a large spot was passing off the Sun's disk, he saw, on either side of the nucleus, these faculae thrown up far above the Sun's surface, like mountain ridges or peaks. Father Secchi, of Rome, re- moves any lingering doubt upon this question. He says : " When a spot is on the Sun's border during its first period, although the dark region (nu- cleus) is not visible, its position is in- dicated by eruptions of metallic va- pors."* This important discovery is confivmed by the observations of Prof. Young, who says : " It is cer- tain that very commonly, if not in- variably, there is a violent uprush of hydrogen and metallic vapors all around the outer edge of the penum- bra 1 ' of the spots. Newcomb's Astronomy, p. 276. It being thus admitted by these learned scientists, that the .spots are accompanied with an eruptive foroe and in fact no one can doubt it philosophy requires us to assume that this power is commensurate witlrthe magnitude of all things with which it is associated. With a powef of such immensity, it would not be sur- prising to find it projecting the light- est of the erupted gases to a distance of many miles miles at least equal to one-quarter of the diameter of the body from which they are projected to the uttermost extremities of the Corona. The known appearances of the faculse are precisely similar to those known of the prominences, oc- cupy the same relative positions upon the , Sun, are in line with the radii of the circle, and the promi- nences are invariably at the base of the marked projections of the Corona, while the spectra of all are the same. The physical fact that these projec- tions are greatest in extent in the direction of the polai region affords no objection to this conclusion. It must be remembered that much the larger proportion of these eruptive spots lie on either side of the Equa- tor, and near thereto ; and as the eruptions are in line of the radii, the projections would, and as a matter of necessity must be, mostly in a direc- tion poleward. This would cause the Corona to be and appear more nearly a cuboid than a spheroid While it is within the range of a reasonable probability that all the luminous matter of the Corona, and much of the luminous matter of the Chromosphere is thrown into space by the eruptive process from these spots, yet it does not follow that all the luminous matter of the latter is placed in its locality, in this manner. Upon any possible hypothesis concerning the body of the Sun, which admits it to be in a highly-heated state whether the matter be in a vapor, cloud, or fluid condition there will be continuouslv emitted from thesur^ 10 THE SUN; 'ITS CONSTITUTION, ETC. face, at all points, in every direction, with comparatively equal force, atoms of heated gases precisely as they are seen to escape from the surface of any terrestrial body when highly heated. These particles, or atoms, united with those erupted, suffice to form the Chromosphere. 12.- CHE PHOTOSPHERE. Within the center of this Chromo- sphere is seen the disk or body of the Sun. This even and comparatively unchanging surface is by astronomers and physicists styled the Photosphere meaning the sphere of light. Of this sphere the unaided eye teaches us nothing beyond its mere existence in a heated and luminous condition. With the aid of a telescope of suffi- cient magnifying power to apparently bring the body within 200,000 miles of us, the details of this surface may, to a slight extent, be studied. Under such an examination it will be seen to present a mottled appearance, Comparable to that of very light and -ieecy clouds. The outlines of these fjloud-like masses are indistinct, and seem subject to constant changes. The same portions will differ at differ- ent times in general appearance to the same eye, while different impres- sions are made upon different visions. Hence the diversities in the descrip- tions given by different observers. Nayemith, of England, examining with the best of instruments, says the appearance presented to him was not unlike that which would be pro- duced by the interlacing of long, nar- row objects, which, running andcros sing in all directions, form a net- work of interwoven willow leaves. Prof. Newcomb says it presents to him the appearance of a fluid in which rioe grains are held suspended. To others, it presents such an appear- ance as might be produced by a body of red-hot iron, at such a distance that the heat waves and escaping gases, coming from it in every pos- sible direction and with every degree of velocity, seemed to constitute a part of the body itself. This uncer- tainty renders a study of its telescopic appearance quite profitless. The only physical fact learned re- garding the Sun's surface by the as sistance of the telescope is, that at or near its equatorial regions, are fre- quently seen, here and there, compar- atively small patches or spots, whose centers are quite dark in appearance, and whose outer rims, while less so. are yet darker than the surrounding surface of the Sun. These spots are found not to be stable in endurance, but to come and go, each independent of the others ; all of which details will be more fully developed as we proceed. The spectrum of the surface is seen to be continuous, giving evidence of matter in such a condition that its constituent parts are in contact, as in the case of solids or fluids, but excluding the condition of free gases. The further details of this surface can be learned only in studying the condition of the matter competing iu 13. THE SUN'S HEAT. The most ordinary experience teaches us that the sun is a source of heat, and since in this day it is not contended that the heat lies in its at- mosphere, it must be conceded that the body itself is in a heated state. By applying the common focus lens we are admonished that it is, indeed, intensely hot, but this instrument does not register the degrees of tem- perature there attained. To deter- mine a mode of measuring these de- grees man has striven for years. Sir Isaac Newton devoted much atten- tion to this subject, and finally form- ulated what was long supposed to be a law of radiation, by which the effective temperature of the Sun could be correctly registered in degrees of the thermometer. This law was based upon an assumed proportionality be- tween the heat radiated and the tem- perature of the radiating mass, which had been deduced from artificial heat. It has since been ascertained THE SUN; ITS CONSTITUTION, ETC. 1? that this basis is erroneous when ap- plied to the Sun, giving the degree of heat in that body as being much higher than it could possibly be. Since Newton's time other theories of radiation have been conceived which have been made to conform to the more accurate knowledge ac- quired and more perfect instruments applied. But the results of different experiments are so variant that no certainty can be attained. Pouillet, Deville and Rosetti differ in their estimates widely, giving respectively 3,000, 10,000 and 18,000 Fahr. as the effective heat of the Photosphere. The method adopted by Rosetti is the most satisfactory to many learned men, while others regard his estimate as entirely too high. It is possible that in the future the spectrum of the Sun-surface will be so read as to ac- quaint us with the true state of the temperature; in the mean time, since all other methods are unreliable, we are left to what inferences may be drawn from such manifestations or phenomena of the Sun as give evi- dence of the condition or state of matter found there. At the temperature given by Ro- setti the most refractory substances known to us, even platinum, fire-clay, and the diamond itself, would be re- duced to a molten state, while most others would be dissipated in vapor or gas but for several philosophical reasons, which will be developed in the further examination of this sub- ject. 14. CONDITION OF THE INTERIOR. Prof. Young, of Princeton College, one of the best authorities upon this subject, says : " The temperature of different portions of the solar envel- ope (Photosphere), must vary enor- mously, increasing as we descend below the surface, so that in all probability there may be a difference of thousands of d agrees between the temperature at the upper surface of the Photosphere and that at the Sun's center, or even at the depth of a few thousand miles."* Prof. Newcomb r in speaking upon this subjeet, says : " For the temperature of the Photo- sphere, it seems likely that the lower estimates are more nearly right, being founded on experimental law, but the temperature of the interior must be immensely higher/' Again, he says: " The be^t sustained theory of the in- terior is the startling one that it is neither solid nor liquid, but gaseous ; so that our great luminary is nothing more than a mere bubble." Indeed all who of late years have given this subject due consideration concur in the conclusion that the interior of the Sun is heated several thousand de- grees higher than the surface. 15. EFFECTS OF HEAT ON MATTER. A knowledge of the effects which heat has upon matter, assures us that a temperature so high as that which must prevail in the interior of the Sun, is sufficient to reduce all matter affected by it to a gaseous state ; but as the process by which this result on matter is secured, is so imperfectly understood or generally forgotten as to lead to important errors in assign- ing this gaseous matter its proper office in the production of other ma- terial manifestations in the Sun, it will be briefly stated. The phenomenon of matter which is called temperature, caloric and heat, is but a status of that matter in which its atoms or molecules, or both, are, as among themselves, in commotion more or less active. The greater the activity of this commotion, the higher is said to be the degree of heat. Now, space is an essential condition of this commotion among the molecules or atoms. In dense matter, one atom or molecule, to make this motion, presses against a neighboring atom or molecule, and to the extent of "Its >power displaces the obstructing neighbor, which in turn displaces its neighbor, and in this manner the commotion is spread * Popular Science Monthly, Nov., 1880. THE SUN; ITS CONSTITUTION, ETC. throughout the mass of matter. This commotion, like all other results from natural forces, is commensurate with the cause. If the cause be great and persistent, the commotion will be ac- tive and powerful. As the commo- tion is increased in these particulars, the pressure for room between the constituent particles rises to a degree of violence, which may be called con- cussion. These concussions increase through the active force producing them, in number, frequency and power, and the distance between one molecule or one atom and another is correspondingly increased, the de- gree of separation being, of course, dependent upon the extent of the force which produces the commotion. If the degree of separation produced is but partial, the matter is said to be in a fluid state, while, if the separa- tion produced is complete and abso- lute, the matter is said to be in a gaseous condition. Thus, when it is said that the matter constituting the interior of the Sun is in a gaseous state, it will bo understood that such a com- motion has been excited and main- tained among the constituent parti- cles of the matter, as to drive them BO completely asunder, that all at- traction of cohesion or adhesion be- tween them has been destroyed and they are left free to move independ- ent of their former associations or connections. It may, therefore, be correctly concluded, that while the higher degree of heat in the interior may be sufficient to reduce matter to a gaseous state, the less degree of heat at the Photosphere may be suf- ficient only to reduce it to a fluid con- dition. 16. TUB EXPANSIVE POWER OF HEAT. The description of heat just given brings us to the consideration of another feature of its effects upon matter. The separation of the con- stituent particles causes them to oc- cupy more space as a whole than when in quiet contact as a solid. That all solids expand and increase in size under the influence of this force is a fact too well known to need proof. The extent to which this ex- pansion may.be carried, even in me- chanics, is shown to be comparatively limitless. The force or power which accompanies this expansion is beyond our comprehension, even when excited by the very limited causes at the command of man. The power of an expanding iron bar is vastly in excess of the fire which produces it ; the ex- pansive power of steam can be made to excel any resistance which may be applied against it, while the irresisti- ble force of burning gunpowder is but the expansive power of heated air. Whoever recalls these well-known effects of heat upon matter, and re- members that this expansion and its irresistible power are inseparable results of commotion among the molecules or atoms of matter, can certainly not fail to appreciate that while the matter composing the in- terior of the Sun is being reduced to this gaseous condition, it is being ex- panded, and tljat this expansion is ;i force commensurate with the cause which put the atoms in such commo- tion as to impel their separation. Yet it is remarkable that this expan- sive force which universally accom- panies the reduction of matter by heat has been overlooked by even the most learned and careful of scholars when treating of the Sun and its phenomena. The importance of this element will be developed as we proceed. As this expansive power in terres- tial matter will prevail over all infe- rior force which may attempt to re- tard or resist it; so the expansive force accompanying the reduction of matter to a state of gas in the inte- rior of the Sun would prevail over any or all inferior forces which rai^ht serve as a hindrance or retarding element. If no retarding forces were arrayed against it, the atoms or molecules would assume their sepa- rate distances, and occupy increased THE SUN; ITS CONSTITUTION, ETC. 13 space without violence, while if, from any source, a hindering force to this expansion was presented, the in- creased space would be secured with a violence necessary to overcome the opposing force. As the two contend- ing forces expansion and resistance increased in power, the violence with which the victory is finally won by the former, might increase in in- tensity until that grade is reached, which is designated by the term ex- plosion. The question naturally pre- sents itself here: Is there any re- sistive force presented to the expan- sive power of the matter being re- duced in the interior of the Sun? Let us see whether this question can be satisfactorily answered. 17. THE SUN'S CKUST. Since it is now quite universally conceded by the learned, that the supply of heat in the Sun is mainly if not wholly maintained by the molecular disturbances produced by the constant contraction of a crust, which has condensed over the more interior portion of the" Sun, an argu- ment to prove the existence of such a crust might seem quite unnecessary. Yet in considering so important a matter as the condition of the Sun, nothing should be assumed, and everything be proven. It were impossible to determine, by philosophy, the existence of the crust without considering the causes which produce it. Therefore, let us ascertain whether there are present in or about the Sun, such causes or forces, as would cause a crust to form or remain over the interior of the Sun. In the very nature of matter and its forces there must be a far less de- gree of heat in the atmosphere sur- rounding than in the body of the Sun. The correctness of this conclusion will be apparent when another study of the phenomenon of heat is made. It is evident that when the commotion among atoms and molecules has so completely separated them, that they are diffused into free gases, that is to say, into their atomic condition, the spaces between the atoms are too great to permit further concussions and rebounds. The instant they cease to come thus in contact, that in- stant the commotion between them begins to decline in activity, and the atoms ultimately relapse into a state of comparative quietude. This dif- fusion into space is a " cooling" pro- cess, the degree of heat decreasing with an increased degree of expansion. Therefore, it is universally true of atmospheric gases that they are, in and of themselves, incapable of en- gendering, or of long maintaining, a heated condition, and must become cold. It will, however, not be overlooked that atmospheric gases immediately surrounding,andin contact with incan- descent bodies, cannot relapse into a condition of absolute coldness, for the reason that the commotion amongthe atoms of the body will be communi- cated by conduction not radiation to the atmospheric atoms in contact, which commotion these in turn will communicate by conduction from ac- tual contacts, or by the interstellar ether always in contact, to neighbor- ing atoms more remote from the in- candescent center, until the effect is finally lost in repetitions or from other causes. Still, the very diffused condition of the atoms thus affected precludes the possibility of their com- motion ever becoming exceedingly active; hence, they must necessarily be in degree of heat immensely below that of the body which they surround a degree of heat BO low that it may be designated as a condi- tion of comparative coldness. The coldness of this surrounding atmosphere produces upon the in- candescent surface of the body re- sults in turn which demand our con sideration. The atmospheric atoms in a state of quietude are in contact with the photospheric atoms in a state of commotion. While the com- motion of the latter would be slightly communicated to the former, as has 14 THE SUN; ITS CONSTITUTION, ETC. just been described, it also follows that the inertia of the atmospheric atoms would serve as a resistive force to the commotion in the body, and, to the extent of this inertia, would put the atoms of the body in a state of quie tude. The proficiency of this quieting force will be greater as the pressure of the atmospheric atoms againstthe others are increased. This pressure will be most powerful in case metal- lic gases which are strongly attrac tive largely permeate the surround ing space. Thus the laws of natural forces and they are the same everywhere require us to hold that matter at the surface of the body in contact with the cold strata of the surrounding atmosphere, must be in a state of quietude, compared with interior atoms, not subject to this influence. Yet it will not be understood that the surface atoms only are thus af- fected, but that the result will follow inwardly as the commotion of each stratum of interior atoms is lessened by the communicated retarding in- fluence, which lessens as it proceeds, and is finally lost in the presence of a greater disturbing influence. The consequences of such a condition of things should now be examined. As has been seen, the commotion among atoms or molecules acts as a repulsive force and separates the atoms. Attraction is a concentrat- ing force, and would bring atoms into close contact. They are, therefore, conflicting forces, the inferior of which will be overcome by the superior. The repulsive force is a created one, which ebbs and flows with the cause that gives it birth, while the attractive force is inherent in matter, and is ever present, ever equally ac- tive, although it may be rendered less effective, and, indeed, entirely over- come by a superior force. It follows then, that the effectiveness of the at- tractive force is in an inverse ratio to the repulsive power. At the surface of the body, and it matters not whether the body be a mere vapor, cloud, fluid or solid, the commotion among its constituent j> articles must be slight when under the influence of such retarding and resisting influences, in which case the attractive force must be effective, and succeed in drawing the atoms into close contact, producing greater con- densation as it proceeds. Density of matter is the result of attraction and attraction only. An irresistable conclusion from these premises, is that the matter at the surface of the Sun, where the attractive force is effective, must be and is more dense than in the inte- rior where the commotion, called heat, has engendered an overpowering re- pulsive force. How deep into the interior of the mass, these condensing powers may in the course of time succeed in overcoming the expansive force can be judged only from effects and results hereafter to be observed. This condensed portion of the mass is designated by the different names of "shell" and "crust," and, as has been remarked, is recognized by all modern writers upon this subject, al- though most of them have invented processes for its formation which are hardly in accord with the principles of natural philosophy, chemistry and mechanics. Such a crust of matter on the ex- terior of the Sun would afford a re- sistance to the passage of atoms of matter through it, as well as to the expansion of matter interior to itself directly proportionate to the density of this crust. Physicists differ widely n their conclusions as to this density, holding either : 1. That it is gaseous and under in- tense pressure ; 2. That it is highly vaporous in density between gases and fluids ; 3. That it is cloud-like a state of density between a vapor and fluid ; or, 4. That it is a fluid. 18. THE GASEOUS THEORY. There are but few scientists at this THE SUN ; ITS CONSTITUTION, ETC. 15 day who insist upon the gas theory. Yet some who are eminent maintain that the shiny appearance of the photosphere is produced by the heavy pressure of the superincumbent at- mosphere upon gaseous matter, and not by its own incandescence. It has, however, been well established that the photosphere is self-luminous, and would shine in any state or con- dition. The gaseous theory is based upon the proposition that the surroud- ing atmosphere rests upon the photo- sphere with great pressure, a proposi- tion which is antagonistic to every known natural law governing matter in a highly heated condition. There is no cause, save attraction, which can produce a pressure of matter in nature, and attraction would be less powerful in the free gases of the sur- rounding atmosphere in a somewhat heated state than in the more con- densed matter of the photosphere. Indeed, as attraction is weak in the gases of the Earth's atmosphere com- paratively unheated and creates too slight a pressure upon matter here to produce any visible effects, so must it be even in a much greater degree with the Sun whose chromosphere is highly heated. Beside this considera- tion, there is another which is quite as conclusive. If the photosphere was gaseous, it could not possibly maintain the immobility of its level, in the presence of the innumerable eruptions which break through the crust in various places, and which would carry away in the uprush much of the surface to indefinable distances from the avenue of their escape, while on the contrary the cavities produced by this uprush are well de- fined and long preserved. The spec- trum, ilso, bears evidence against the theory, which cannot be gainsaid. But we will not pursue all the facts which controvert this theory, at this point, as most of them bear equally strong evidence _ and cloud theories, in tion of which many will be reviewed. against the vapor the considera- of these facts 19. THE VAPOR THEORY. A respectable number of distin- guished physicists conclude the pho- tosphere to be in a vaporous condi- tion. Prominent among these was Father Secchi, and is Prof. Langley of Pennsylvania. The former says : " The photosphere is a mass of sub- stances, mostly known to us, raised to an enormous temperature, and in a state of vapor, whose spectrum is rendered continuous, either by the heat or the pressure to which the vapor is subjected." He is, however, undoubtedly undecided as to the de- gree of density to which his supposed " vapor " may have attained, as in the course of his elaboration, it will be observed that he conceives it to be so strong in its connection and this is incident to condensation only as to present such a resistance to the expansive force within, that the latter frequently breaks forth "in strong and violent eruptions." Prof. Langley, not intending to be misunderstood upon the question of density, says : " The photosphere is purely vaporous, and I consider the upper (outer) vapors to be lighter than the thinnest cirri of our own sky." As the cirri are the very lightest and least dense of the most vague and fleecy of the perceptible hazes float- ing highest in our sky, we need not misapprehend his meaning. Yet, like Father Secchi, the Professor could not have sufficiently studied the subject to methodize his own thoughts, for later on he makes this significant ad- mission. "The Sun spots give evi- dence of cyclonic action, such as could only occur in a fluid." 20. THE " CLOUD-LIKE " THEORY. There are physicists of high stand- ing, who, recognizing so many phy- sical evidences precluding the con- clusion that the photosphere can be either gaseous or vaporous, say that it is matter in that condition of den- sity which is a step nearer the liquid than vapor, and call it " oloud-like." Ifl THE SUN; ITS CONSTITUTION, ETC. Of 8neh are Prof. Faye of Paris, and Prof. YouDg of our own country. Prof. Faye in his incomprehensible manner of expressing his thoughts, says: "There are ascending vapors from the interior which go to form a cloud of condensed matter." We close the quotation here, lest if we pursue it, the thought be lost in thickening confusions. Prof. Young says: "The visible surface of the Sun, the photosphere, is composed of clouds formed by the condensation and combination of such of the solar gases as are cooled suf- ficiently by their radiation into space." Fearful that this slightly condensed mass would not be suf- ficiently strong to present so much hindrance to the expansive force from within as to produce the violent erup- tions seen at the Sun-spots, or entire- ly forgetting the presence of this ex- paneive power, he invents the follow- ing ingenious theory to account for the explosions. " The weight of the cloud-shell, and the resistance offered to the descend- ing products of condensation (from the interior side of the shell into the interior of the mass), act to produce on the enclosed gaseous core, a con- stricting pressure, which forces the gases upward through the intervals between the clouds with great veloc- ity." It is very probable that the Pro fefisor would be astonished at the ig- norance of the person who, not knowing the real cause, should re- mark in his presence that the heated gases of the Earth's interior were forced up through the Earth's crust at the volcanoes, by the weight of the crust and the atoms falling from its innerside into the gaseous core ; and upon recovering his equilibrium, would correctly inform him that this phe- nomenon was produced by the mighty expansive power of the heated matter within. Certainly he is mindful of the fact that the crust of the Sun would have no weight upon the more interior portions, and that " products of condensation r would not fall into the interior except through the power of attraction, which is wholly ineffect- ual in the presence of such immense- ly high temperature as reduces mat- ter to gases. Here a remark made by Prof. Simon Newcomb is apposite. He says: "Since the properties of matter are the same everywhere, the prob- lem of the physical constitution of the Sun is solved only when we are able to explain all solar phenomena by laws of physics, which we see in operation around us. The fact that the physical laws operative on the Sun, must be, at least, in agreement with those in operation here, is not always remembered by those who have speculated on the subject. 1 ' 21. SUPPOSED SUPPORTS OF THE FOREGOING THEORIES. The gaseous, vapor, and cloud theories have not been arbitrarily assumed, regardless of facts and care- less of consistencies, but on the con- trary, their respective advocates seem driven to the adoption of them as the only hypotheses upon which many of the solar phenomena can be at all accounted for. Most prominent among the phenomena, seemingly re- quiring this rare condition of matter, are supposed to be those seen in, or about the so-called Sun-spots. For instance, spots have been observed to change their locality on the surface of the Sun, with a velocity of 1,000 miles in a second of time, which, it is urged, could not take place in a density greater than that of vapor. But the error of this conclusion lies in the thought that the spots are "substance " moving through matter. The truth is, the spets are only cavi- ties, and we are required, not to con- ceive the possibility of one body of matter moving through another at this velocity, but only the possibility of a given body of matter changing its own relations at this velocity un- der an inconceivably immense press- THE SUN; ITS CONSTITUTION, ETC. 17 ura, aided by the most violent vol- canic action forces which are sus- ceptible of gaining such power as would suffice to hurl the entire body of that mighty luminary in fragments for millions of miles, in the twinkling of an eye. A more prominent phenomenon connected with these spots which is supposed to require this rare condi- tion of matter, is a supposed sepa- rate arid distinct movement of them (the spots) from the Equator toward the poles, and toward the Equator from the latitudes, which, if true, is unmistakable evidence of separate currents of movement in the matter of the photosphere itself a feature which could exist only in the rarest of matter. Upon the real existence of this phenomenon observers are not agreed. Some report having seen spots move poleward, others re- port having seen them move toward the Equator, while others see nothing in them which they regard as such a movement. Prof. Faye denies such a motion, and says: "These strips (of separate currents, in which he also conceives them moving, on ac- count of a supposed movement other than this), move nearly parallel to the Equator, and never give indica- tions of currents constantly directed toward either pole." Yet, there can exist no doubt that under the prevailing conditions, these spots do present the appearance to some minds of moving longitudinally as described by the observers who re- port them. That this is however an optical illusion, is rendered evident by the following considerations. Let a" spot be selected which is midway between the eastern and western limbs of the Sun, and at thirty degrees above the Equator. Here, the eye and mind appreciate only the alti- tude of the spot from the Equator, which, say, is 143,310 miles, and are wholly unmindful of the fact that the spot is also farther from us than the Equator by 21 ,500 miles. The circular angle of the hypothenuse of this tri- angle whose base is 21,500 miles, and whose altitude is 143,310 miles is lost to the mind by the foreshortening in- cident to its direction in the line of sight. As the Sun rotates, this spot is gradually carried toward the west- ern limb, and as it moves on, this angle of the hypothenuse becomes more and more appreciable both to eye and mind, until when the lirnb is reached, the angle of 214,980 miles is duly appreciated, and the spot has thus seemed to have moved a distance of 71,670 miles from the Equator. Hence, an observer watching a spot passing from near the center of the Sun toward the limb, is ready to as sert that it has in fact moved from the Equator. An opposite illusion will present itself to the person who selects a spot when making its ap- pearance on the limb of the Sun, and watches it while approaching the center. When first observed by him, his mind fully appreciates the angle there presented, and recognizes the spot as being 214,980 miles from the Equator. As it approaches the cen- ter, however, this angle constantly foreshortens, so that when the cen- tral position is reached, the spot seems but 143,310 miles from the Equator, and/ this observer is also ready to swear that he has observed spots move toward the Equator.* Hence, these supposed conflicting movements, neither of which is real, vanish from the list of physical phe- nomena that seem to render neces- sary the theories of extremely rare matter in the photosphere. There is, however, a supposed movement of these spots, which ia universally recognized by observers, and which serves as the ruling ne- cessity for supposing the surface of the Sun to consist of extremely rare matter. In the year 1859, Prof. Carrington reported to the world of science, that the spots immediately on or near the Equator of the Sun * The disk of the Sun appears flat, and neither the eye nor mind appreciates its ro- tundity. 18 THE SUN; ITS CONSTITUTION, ETC. moved to the westward with greater velocity than those at any of the latitudes, while the movement of spots on latitudes nearest the Equator was invariably more rapid than on the latitudes more remote. Immediately upon this announce- ment, every telescope in the civilized world was focused upon the Sun- spots, and a very few hours' observa tLn sufficed to confirm the dis- covery so recently made. Whether comptnion spots at the Fquator and on a high or low latitude, or on several latitudes, at or near the cen- ter, at or near the eastern or western limb were selected, in every instance the spot on the Equator was seen to move more rapidly than one on any of the latitudes, while on any lower latitude the motion was found to be more rapid than on any higher one the movement regularly decreasing in velocity on approaching the poles. No sooner was this difference in r the velocity of rotation universally j recognized as an actual physical fact, than the savants, knowing the spots did not move tnrough the matter of the photosphere, but with it, wisely concluded th :t at least the outer <;over of the photosphere, in which the spots moved, was but a gaseous, vapoious, or cloud like substance, moving in separate currents parallel to the Equator, each with a differing velocity. M. Fayo formulates the conclusion as follows: " The contiguous strips, (lines of currents), of the photosphere, are animated with a velocity of rotation nearly constant for each filament (slender strip), at least during a pe- riod of several months or years, but varying with the latitude from one strip to another." It is not designed to combat in detail this theory of separate cur- rents or movements, yet for the pur- pose of making apparent the thought- lessness of many speculators in con- structing the premises upon which to found their theory, the following pro position is advanced: If the rotation velocity of these separate currents on the photosphere differs for every ten degrees of de- parture f r om the Equator poleward, then also must the velocity of the cur- rents vary proportionately for every ten inches of distance. 'This being true, it follows that however little the distance by which one spot exceeds another in remoteness from the Equator, there must be a difference in the velocity of each, since their rota- tion velocity is determined by the rotation velocity of tho currents. Suppose two spots, 15,033 miles each in diameter, tho one being 1 o,003 miles from the Equator, the other lying in right line at a distance of 00,000 miles from the Equator. No\v, suppose a spot just westward of these two spota, to be equal in diameter to tho diame- ter of both the other spots, and tho distance dividing them. Each of the two smaller spots, under the theory, must be moving in sepa- rate currents the difference in their velocities being many hundreds of miles per hour. The large spot must move in these two currents, also, in as much as it is right on the heels of tho two others. *" Now, will these theorists inform us why it is that the large spot is not torn into frag- ments by these separate currents of different velocities? Large spots and smaller ones aro seen moving without disturbance, in clusters, every year, right in the face of these theorists, who appear never to have noticed them, or if so, regarding the phenomena as of vastly less import- ance than their theories. The truth concerning this rotary velocity of the spots is quickly told. There is precisely that difference in the speed with which they rotate at, or away from the Equator, which Prof. Carrington has reported. He made separate daily observations of spots upon the Equator, and found the daily angular velocity of rotation to be 865', while several daily observa- tions of spots at latitude 30, showed: THE SUN; ITS CONSTITUTION, ETC. 19 their daily angular velocity to be 816'. From these observations it was deduced as a legitimate mathe- matical conclusion, that as the latitu- dinal spot moved slower by 49' daily than a spot on the Equator, it would require one more day to complete its revolution and hence the move- ments are, and must be separate. The error of this conclusion is ren- dered apparent by the statement of a few very simple mathematical pro- positions. The Sun at the Equator is 860,000 miles in diameter, and in round num- bers 2,580,000 miles in circumfer- ence. At a latitude of 30, suppos- ing it to be a perfect sphere, it is 81 7,000 miles in diameter, and 2,450,- 000 miles in circumference. It is evident that a spot on the Equator would be required to travel 103,200 miles daily, in order to complete its circuit in twenty-five days, while a spot at 30 latitude could make its circuit in twenty-five days if it trav- eled but 98,000 miles per day. In other words, the latitudinal spot traveling 5,160 miles less each day would complete a rotation of its smaller circuit in the same period of time occupied by the equatorial spot in making its correspondingly greater one. Hence the matter of the pho tosphere at the Equator, and at the latitude of 30, has not changed its relative position notwithstanding this difference in rotary velocity. The same results would be present on a globe of the most solid iron. Here observers have not been mis- led by an optical illusion, but have erred by drawing a conclusion from a partial fact only. Prof Carrington and other observers have noted the rate of speed with which a spot on the Equator moved for a few days, then in like manner the rate with which a spot on some of the latitudes has moved ; and discovering the dif- ferences in the rate of velocity without stopping to consider the dif- ference in the distances which each had \o move on account of the rotun- dity of the body have drawn the erroneous conclusion referred to, and which has forced many a deluded spectator, like M. Faye, to rack his brain over every species of currents, except a current of thought toward the misleading error of deduction. It must now, however, be deemed conclusively settled that the differ- ence in the velocity of the spots at the Equator and latitudes is no evi- dence of a movement of the matter constituting the photosphere, and hence presents no necessity for the assumption of matter in so rare a condition as gas, vapor or cloud. There are, however, many physical facts now known of the Sun which bear strong evidence against so rare a condition of matter at its surface. The spectrum assures us of an inten- sity in its heat which could not possi- bly be attained and held by matter so rare. This spectrum is neither of lineal nor of fluted bands, as would be the case if the molecules were in so imperfect contact as indicates gaseous or vaporous conditions, but on the contrary its continuous fea- ture is conclusive evidence of matter in a state not less dense, at least, than fluid. The difference in the rotating velocities of the spots, which was so long regarded as conclusive evidence of matter in a very rare state, must now be held to be as conclusive proof that this surface is in a condition which at all points maintains its re- lations ; and to this extent is evidence against either a gaseous, vaporous or cloud-like density. The absence of oblateness in the Sun, with its velo- city of rotation, is also conclusive evidence against these theories, it being incontestable that centrifugal force arising from a given rotary velocity will posses an effective power proportionate to the rarity of the matter on which it operates. The photosphere could not, in the presence of such frequent and violent eruptions as admittedly prevail there, main- tain its continuous level and un- changing rotundity if in so rare a 20 THE SUN ; ITS CONSTITUTION, ETC. condition, but on the contrary, large be required to contract but 220 feet portions of it would be continuously : a year in order to produce its present displaced. Again, such violent erup | heat.* We are not aware of the basis tions could not possibly obtain in a ' of this calculation, but it is evident body whose surface afforded no great that the contraction would have to er resistance to the expansive force exceed these figures very largely, if of the interior heat than would be | the matter be more rare than quite a presented by gases, vapors or clouds. | dense fluid. Still again, in such light and easily j At this point, however, it may be disturbed matter the spots would not I well to suggest that attraction exerts and could not maintain their existence, I no pressure upon gases atoms in a their forms, and even the minutiae of j state of commotion called heat al- their projections, depressions and ! though it will exert a drawing pressure sharp angles for mouths, as they are known to do. Another disproving physical fact is found in the method by which the heat supply is maintained in the Sun. However wild or unnatural may be the theories of most speculators con- cerning the Sun in relation to all else, they are each, by our advanced knowl- edge of this subject, compelled to ad- mit that the heat of the Sun is en- gendered by the friction between atoms when coming in contact, while in process of contraction or conden- sation, to produce which, the outer .atoms move inward If it were ne- cessary that the atoms should move to any considerable distance to be brought in contact, the Sun would diminish in dimensions rapidly. In matter as rare as gas, vapor or clouds, the atoms are so remote from each other, that in order to bring them into actual contact, a considerable movement would be required.* We have no evidence of any perceptible diminution in the size of the Sun since man first measured its disk ; while the angle which it distends would have grown visibly less in that gaseous and must either upon atoms in a state of quietude, when they are no longer gases, but atomic substances and that if the surface of the Sun is gaseous, there is no power to hold them in contact, nor cause them to draw closer together. Hence the advocates of the vaporous conditions abandon their theories, or disprove that the heat supply of tho Sun is kept up by the process of contrac- tion. 22. - TIIK CRUST IN A FLUID CON- DITION. A few words now concerning the theory that the Sun crust is a fluid. But few modern scientists have had the hardihood to urge this theory in the face of the many apparent facts BO long and so forcibly presented as proofs of matter in a rarer condition pecially those supposed to exist in the movements of the Sun spots. Yet some of the very ablest of rea- soners, without attempting to account for these movements, but intuitively feeling that they had not yet been clearly nor correctly understood, af- ter viewing the whole field and seeing period, were the matter of which its | so many p i a i n an a incontestable phe- surface is composed so rare. Philo- sophically, we are constrained to ad mit that in order to maintain the heat supply, that body is in fact con- tracting in size, yet it must be slowly. An estimate has been made in which it was concluded that the Sun would * It is unphilosophical to think of the phe- nomenon of heat being produced without a contact of the atoms. nomena in absolute conflict with the conclusions of the theorists, have de- clined to accept either the gas, vapor or cloud hypothesis. Most prominent of this class of independent thinkers stands Prof. Simon Ne \vcomb, who, while dissenting from these theories and declining to present one in their Newcomb's Astronomy, page 519... THE SUN; ITS CONSTITUTION, ETC. stead, yet suggests one in very sig- nificant language when he says: "The opinions of students respect- ing the constitution of the photo- sphere, are so different that it is hard ly possible to express any views that will not be challenged in some quarter. Although a contrary opin- ion is held by many, we may venture to say that the rays of light and heat aeem to come not from a^as, but from solid matter. This is indicated by the fact that their spectrum is con- tinuous, and also by the intensity of the light which far exceeds any that as has been made to give forth t does not follow from this that the photosphere is a continuous solid or crust, since floating particles of solid matter will shine in the same way. That it is not continuously solid, like our earth, seems to be fully shown by the variations and motions of the spots, which have every appearance of going on in a fluid."* All the reasons which have been advanced against the gas, vapor, and cloud theories, are equally effective affirmative supports of the hypothesis that the photospheric matter is in a condition at least as dense as the very densest of all our fluids. In the face of the frequent changes which are seen in the Sun-spots, no one would have the temerity to re- gard the matter as solid. That this fluid must have a density beyond that of water, is made evi- dent by the persistency with which the very details of the spots are sity of mater must be found in this crust. It has been for years conced- ed by physicists, that taking the vol- ume of space occupied by, and the force of gravity in the Sun into con- sideration it was a correct deduction, upon a strictly mathematical basis, to say that tho density of the body, as a whole, was greater than water by 1.414. This being true, and who would now dispute it? and it be- ing further true that by far the great- er density of the body must exist in this crust, it follows as an irresisti- ble and incontrovertable conclusion, that the matter of the Sim's photo- sphere is in a condition far denser than water. Considering how vastly inferior in quantity of matter this crust must be when compared with the immense interior, it would not be entirely em- pirical to say, that the matter of this crust is as dense as tar, or not greatly unlike heated iron in that condition when it is fitted to run into molds. 23. PRODUCTION OF THE SUN SPOTS. With matter of such density form ing the crust of the Sun, there can be no difficulty in understanding how it presents a resistive force to the ex- pansive power of the heated matter within, nor will doubts exist in the mind of the observer as to the suffi- ciency of this resistance, when over- come by a superior power, to pro- duce such violent eruptions as not only form immense cavities within its depths, but whose lateral pressures maintained, as well as by the well de- j serve as successful aids in their long maintenance. So can it be easily un- derstood how the violent uprushof the fined forms into which it is broken by the violent eruptions on the break- ing out of these spots. A more con- clusive fact on this point is found in the following relations. It is con- ceded that the entire central region of the Sun, indeed all but a mere exterior crust, is in a highly gaseous state, whose density must be rare, very rare, and that the greater den- * We omit the words * p orgas" here for the reason that he immediately proceeds to show it could not be gas. erupted matter, following, of course, the radii of the sphere, produces cavities not unlike inverted cones in form, the angles of whose *udes are made greater than the angle of the radii by the wash incident to the lateral pressure of the out-rushing metallic gases, thus producing the penumbra of these spots, the lines of projections and depressions precisely as they are seen by the telescope. THE SUN; ITS CONSTITUTION, ETC. 24. THE AREA OF SUN SPOTS LIM- | ITED. We are aware that the outward pressure of these interim expanding gases would be equal on every con- ceivable portion of the enclosing spherical walls presented by this crust, and that, under this sole influ- ence evidences of these eruptions would be as likely to be seen on one portion of the surface of the Sun, as on another; while in truth but one instance has been known of an erup- tion above 40 latitude, though thou- sands have been observed on and near the Equator, From a series of ob- servations extending over a period of ten years, and comprehending 1,700 spots, Prof. Loomis compiles the fol- lowing table, giving the per centage of their occurrence m different locali- ties: LOCATION OF SPOTS. j q s 7 3 ii LOCATION OF SPOTS. m M Beyond 30 North L at. Between 20 & 30 " 10 & 20 " M o&io Beyond 30 South Lat Between ao & 39 " " 10 & 20* " " o&io" " 2 15 7 12 By this table it is seen that twenty- three per cent, of the spots appear upon or within ten degrees of the Equator, and sixty-three per cent, within twenty degrees, while but thirty-seven per cent, occur at a greater distance, and comparatively none beyond thirty degrees. No one has ever attempted to account for this limitation of the Sun spot area. Faye, Langley, Young and New- comb, are silent upon this subject, while Father Secchi says, " It is re- markable that the parallel of thirty degrees divides the hemisphere into two sections of equal volume." He further recognizes these sections as exceeding all others in activity, but does not attempt to show why it is so. Yet, in concluding that these are the most active regions of the Sun, the learned observer has mistaken evidence of activity for activity itself. The spots are but evidence of inte rior activity, which has made itself apparent in these particular regions only, owing to some cause which he has not sought to divine, but which is explicable on the most satisfactory basis. The expansive force of the strug- gling interior heat is exerted equally upon all sides of the enclosing walls the crust and would break through wherever these walls were weakest; and if they were constructed by a uniform force attraction or gravita- tion there can be no reasons for supposing them to be weakest in the region of the Equator. What would be equal to such a weak spot in the walls, however, would be some force acting in conjunction with the expan- sive force at some points on the crust which did not combine with it in equal power at other points. Is there such a combination of forces at or near the Equator? The Sun is rotating on an axis once in every twenty-five days. The cir- cumference at its Equator is about 2,580,000 miles, and hence a given point upon it moves through space at the rate of 103,200 miles per day, 4,300 miles per hour, and one mile and eighteen-one hundredths of a mile for every second of time. It is known that rotary motion engenders centrifugal force and that the degree of this force is proportionate to the velocity. With a velocity as great as that prevailing at the Equator of the Sun, this power, which would draw the matter away from the center and hurl it into space, must be immense. This force, however, while greatest at the Equator, is existent at every conceivable degree of latitude, lessen- ing regularly in power, of course, with the decrease of velocity, as ob- served on approaching the poles, un- til when forty degrees are reached, the power is very weak, as the ve- locity is very slow. While the centrifugal force would be greatest on, and in the immediate vicinity of the Equator, yet it would not materially vary in power for the THE SUN; ITS CONSTITUTION, ETC. first few degrees removed, and a slight inherent weakness in the crust at these points would equal the dif- ference in the strength of the centri f ugal force. It is not entirely specu lative to conclude that this identica" centrifugal force, during the process of condensation has weakened the crust at some little distance from the Equator on either hand, by draw- ing down to the Equator from these regions, matter which the attrative force would otherwise have distribu- ted equally throughout the condensed crust. Hence it is seen that the two forces, centrifugal and expansive, have combined most effectively in the very region of the photosphere where these spots are found to be most fre- quent and most active. Who will doubt that these forces determine the region of the Sun spots. 25. PERIODICITY OF THE SPOTS. It is also urged that the expansive and centrifugal forces are constan t, and that under like prevailing conditions they must produce continuous and uniform results, while the frequency and activity of the spots vary in pe- riods of time. But it must not be forgotten that their variance has about it, in a general way, such reg- ularity as to approach periodicity. There is a period when in fre- quency, numbers and activity they are at their higtit; then they begin to decline in these particulars, and continue so to do for five or six years, at which period they reach the mini- mum of activity ; again their fre- quency, number and activity begin to increase, and continue so to do for five or six years, when they reach again the maximum the period from one highest point to another, or from one lowest point to another, generally being found to be about eleven years. Prof. Newcomb says of this pe- riodicity, that no satisfactory explana- tion of its cause has yet been given. Father Secchi says : " Whatever may be the cause of thesa changes of activity, we are completely ignor- ant of it. M. Faye, who does not seem inclined to acknowledge a want of full knowledge on any topic touch- ing the Sun, yet says of this: "It is mure difficult to account for the pe~ riodicity of the spots." Prof. Young- says : " I am unable to think the pe- riodicity of the spots due in any- way to planetary action ;* at least y the evidence appears to me wholly in- sufficient as yet, but I have no hy- pothesis to offer." Upon the hypothesis of the expan- sive power of the interior gases, this phenomenon is susceptible of the mo^t satisfactory explanation. All are aware that the longer we successfully restrain engendering steam, thegreat- er the power it attains. We are also- aware that when the pressure of the steam has reached a high point, if we permit some portion of it to escape, the pressure is relieved just to the ex- tent of the escape. Upon closing the avenue of escape, the steam again begins to gain head and pressure, and will repeat this ebb and flow just so many times as we open and close the escape. Suppose, now, in the case of the Sun that a large number of spots appear, through which the heated gases from within are permitted to- escape in immense volume for days. While this escape is going on, the pressure is being relieved precisely in proportion to the amount of matter which has been ejected, and as this pressure decreases, there is a corres- ponding decrease in the number of lew cavities produced. Finally, the entire pressure outward is exhausted, when the lateral pressure of the es- caping gases is withdrawn from the sides of the eavities, which are then 'orced inward by the pressure of the iquid matter of the crust, in an effort o seek a level, and the cavities are ;losed. Upon the closing of these * Strange to say, many learned men have attributed this periodicity to Jupiter, whose eriod of revolution is somewhat coincident with them. 24 THE SUN.; ITS CONSTITUTION, ETC. cavities, or avenues of escape, the in- terior heat begins to gain head and continues to do so until it (in combi nation with the centrifugal force) be- comes superior to the force of resist ance arrayed against it by the crust, when it again breaks forth in all its first vigor. Thus, the expansive force furnishes the causes for its periods of activity and exhaustion. Could any thing be more evident? But, it may here be asked, why are these vibrations from one extreme to the other measured by comparatively equal periods of time. The answer is found in this proposition : The same constant forces acting upon the same volume of matter under like re- curring conditions must prodi.se uni- form results. It is evident that so fast as the matter of the interior of the Sun is thrown by the eruptions into the sin-rounding atmosphere, it is cooled, and by the force of attraction brought back to the outer surface of the crust, where it enters into the pro- cess of condensation, supplying to the exterior the identical matter taken from the interior while the interior itself is refilled by the contraction of the more outward portions. Thus, for ages, will the same forces exist and continue their work upon the same volume of matter restored by- repeated processes under like condi- tions, and, if one century ago it re- quired eleven years to complete the circuit of this work, there remains no reason why it should not require about eleven years to repeat it again one hundred years hence. True, the causes would not produce a companion re- sult again in precisely the same pe- riod as before often not within a year, perhaps not within two, and at times not within three years; nor are the maxima of these spots more reg- ular than this, as will bo seen by ob- serving the table prepared by any ob- server. $ 26 THE SPOTS AHK CAVITIES IN THE SUN. Although much space has been oc- cupied in considering this particular phenomenon, yet it would be improp- er to omit a notice of the proof ad- duced by observation of the concavity of these spots. As early as 1684, Cassini, one of the first observers with the telescope, declared that he had seen a notch in the limb of the Sun, directly upon the point where a Sun-spot was just go- ing off. Since his time, a number of other observers have witnessed the same appearance, both when the snots were coming on and going off. If further proof of this concavity were needed, it is abundantly afforded in the perspective presented by them while passing from one limb to the other. In 1869 Prof. Wilson, of Glasgow, made such close examina- tion of a series of spots, for the pin pose of ascertaining the real facts of this phenomenon, that no physicist now doubts that these spots are im- mense cavities in the crust of the Sun. From the angles presented by the changes made in the penumbra, Wil- son estimated the depth of the crust to be 4,000 miles, which is in effect, an estimate that for a distance of 4,- 000 miles, the crust is sufficiently dense to preserve form and maintain distinctive features. Other estimates have been made upon like observations with some- what varying results, Prof. Young concluding that the crust could not | be less than 10,000 miles in thickness. These spots, then, are found to be immense hole.*? in the body of the Sun. whose diameters range from 13,000 to 100,000 miles, and whose depth is estimated from 4,000 to 10,000 miles. The walls or sides of the cavities form what is called the penumbru. and to an imperfect or weak instru- ment present the appearance of u broad inner rim, extending from the outer circumference cenlerward, to a more central portion of the spot, which is darker in color, and called the nucleus. These walls are not of uniform color, but are streaked with light and darker lines, running from THE SUN; ITS CONSTITUTION, ETC. 25 the exterior to the interior, and pre- senting to the eye the appearance of washes or gutters on a clay -bank or hill-side. While the central portion of the nucleus is darker in color than the penumbra, it is by no means black, nor does it appear to serve as the bottom of the cavity. Rather it pre- sents the appearance of being the dim light of luminous vapor away down in the regions of the solar interior seen through these openings in the crust. By a close observation it will be ascertained that the eruptions from the spots are most active upon their first appearance, during which time the spectroscope detects among the escaping gases those of the heaviest metals, such as iron, nickel, magne- sium, and sodium, while as the activ- ity subsides their presence grows less frequent, until when the spot is on the point of closing up they are not seen at all. When the spots are most active the faculse heretofore spoken of are most generally seen. It has been shown that these fac- ulae are but the prominences seen during an eclipse, and recognized as glowing hydrogen flames shooting out with inconceivable velocity through the chromosphere, and in the direc- tion of the Corona. When we consider the mighty fires which are raging within the interior of this vast body, the Sun, and the irresistible power of the expansive force created by it, in connection with the immense resist ive force which must be presented by a crust of such density and depth, it will not be deemed marvelous that at times the heated gases break forth with an explosive power so great as to hurl them into space through these cavities in the direction of the faculae and prominences, until the lightest of them is seen in the Co- rona and even in the projections, a distance of not less than three hun- dred thousand miles.* * Some have estimated this power to be sufficient to hurl the matter to a distance equal to that of the Asteroids from the Sun. 27. HOW THE HEAT OF THB SUN REACHES THE EARTH. Having ascertained the manner in which the heat of the Sun is engen- dered, it becomes of interest to know how that heat is communicated to the Earth and other planets of the solar system. We have learned that the phenomenon which we call the heat of the Sun is but an active commotion among its coastituent particles, as all heat is but motion in atoms of matter. We have now but to ascertain in what manner the commotion in the atoms of the Sun can be commu- nicated to the atoms comprising the Earth or the other planets of this system. In the first place, it is no longer held among scientists that the at- mospheres of the Sun and its satellites are each limited in extent, and bound- ed by clearly defined lines, the spaces between being void of matter, and hence vacuums ; but, on the cor- trary, it is no*v admitted by nearly all physicists that the respective at- mospheres of all the planets, and of the Sun, are densest at the surface of the bodies, gradually growing more rare outward until at length but one substance constitutes it, and that substance a very rare one in- deed. For the want of a more spe- cific name the terms " luminiferous ether " and "interstellar ether" are used to distinguish it from the other substance in Nature. This ether pervades all space everywhere and in all directions. It not only fills the space lying between neigh- boring planets, "but also all space, however small, existing between each atom of matter constituting the plan- ets and their atmospheres. Hence, all the way along the 92,700.000 miles from the Sun to the Earth this ether exists, starting from within the surface of that luminary in the di- rection of every conceivable radius of that spherical body, filling the inter- stices between the atoms composing THE SUN; ITS CONSTITUTION, ETC. the chromosphere, as well as those of j municated to the atoms composing its cooler atmosphere, and when ' our atmosphere, as well as to all other reaching a point still further outward | matter on or about the surface of the where no other substance is encoun-j Earth. This motion of the atoms so tered, it occupies the entire dominion. ; differs in certain particulars from nil Reaching the outermost regions of the atmosphere of the Earth, or any other of the planets, it mingles with the atmospheric gases, filling up the interstices, and pressing on- ward to the surface of the planet wher^ it in like manner crowds itself into every space, whether it be cavity or pore, of the body itself. other motion in matter, as to produce upon the sentient nerves by contact a sensation so different from all other sensations as to be readily identified; and this sensation we have denomi- nated heat. It is not within the legitimate prov- ince of this essay to describe the phenomenon of heat and its method While this ether, from its nature, ' of transmission, yet it will not be is wholly im perturbed by attraction or gravitation, yet it is extremely sensitive to every other known force. Like all other matter it is unquestion- ably composed of atoms, but whether its combination is complete in the single atom, as in mercury, or whether two or more of these atoms are com bined into molecules, is unknown, but the chromic effects of light can be best accounted for upon the hypothe- sis that it is molecular and that its molecules are composed of not less than two, nor more than three atoms. Although thus combining with itself, it has no affinity for other substances, and hence is never disturbed by ab- sorption or combinations, and there- fore ever presents the same volume and maintains the same universal profusion. wholly out of place to say that the motion of the atoms is transmitted through space by this medium, in a tremulous or vibratory movement that goes onward at a rate of speed which is ever indicative of the degree of activity in the commotion among the particles or atoms of the heated body radiating them. Hence, if the com- motion in the Sun is very intense that is, if the heat be high the undu- lations will be very rapid, while if the commotion be less active, the undula tionj will be slower. Thus, the rate of speed observed in the so called heat-waves is evidence of the degree of heat attained in the emitting body. As the heat in the Sun is intense, the vibrations of its heat-waves are very rapid. In this manner the heat We have seen the atoms or mole- 1 of the Sun is transmitted to the Earth cules of this ether mingled with the and made sensible to us. atoms and molecules constituting the The light of the Sun is communi- Sun. Its atoms thus in contact have jcated in precisely the same manner, imparted to them, by concussion, the Here it is proper to observe that light, commotion prevailing among the like heat, is no longer regarded as atoms of the Sun. The atoms thus set i a substance, but is admitted to be in motion communicate motion in turn 'only that phenomenon which is pre- to their own neighboring atoms out- sented to the sentient nerves we call ward, these to their outward neigh- bors, and so on, until the commotion is transmitted to the uttermost out- ward limits occupied by the ether, optic, by such an intense commo- tion among the constituent parti- cles of a body of matter, as drives these atoms completely asunder, de- intersecting in the path the planets ; stroying their cohesion, causing them Yulcan, Mercury, Venus, Earth, Mars, j to separate and assume their atomic the Asteroids, Jupiter, Saturn, lira- condition. Hence, light is a phe- nus and Neptune. At the Earth the | nomenon accompanying the phenome- motion of these atoms is also com- 1 non which we call heat, that is pro- THE SUN; ITS CONSTITUTION, ETC. 27 duced by a particular degree of motion among atoms in commotion. To make this clear, let us by any ade- quate means at our command put in motion the atoms composing a bar of iron With the least motion engen- dered we have produced some degree of that commotion which the sentient nerves begin to recognize as heat, and yet the optic nerves have not been able to appreciate the sensation. We increase the motion until it has reach- ed that degree indicated by the Fahr- enheit Scale as 976, when the merely sentient nerves are largely impressed with the sensation, and yet the optic nerves have not been sufficiently touched to respond. Let the motion be increased one degree more, to 977, and instantly the optic nerves become sensible to the existence of this con- dition, and recognize the phenomenon we call light. The body composed of the atoms in commotion is now be- coming luminous, but its light is faint, being barely perceptible to the vision. Run the motion up many degrees more and the body becomes intensely radiant. It is red-hot iron. At this stage a large proportion of the con- stituent atoms are being set free from their former relations, and assume their separate atomic condition. A degree of commotion analogous to this but still greater has been attained in the Sun, and hence it is not only what we call heated, but also self-lu- minous. The vibrations of the undulations or tremors indicating this luminous condition have been found to travel forward 185,500 English miles in one second of time, and hence to pass from the Sun to the Earth in about eight minutes. Recent satisfactory experiments have developed at least two facts in electrical science which render a few remarks relative to electricity not improper here. It has been ascer- tained, first, that electricity is but a manifestation of heat, and secondly, that the medium which transmits light will also transmit electricity. The highly agitated condition of the Sun, more especially during the great- est activity of the Sun-spot periods, must, and certainly does develop among the atoms of that body a very high degree of that particular com motion which we denominate Elec- tricity. This motion is communi- cated to the inter-stellar ether in the mariner above described, and by it is transmitted to the atmosphere of the Earth, and of all the other planets as well. Hence, it is not at all strange that there should be periods of electric disturbance in our atmos- phere which correspond with the periods of the Sun-spots, but on the contrary such results would be most natural sequences of a cause which philosophy thus connects with them. The Aurora Borealis is also thus ac- counted for upon the most scientific basis. In addition to this, it has long been observed that the magnetic needle is subject to irregular but periodical changes which are distinct from that regular variation which occupies years in making a cycle, and these changes can now be philosophically traced to those unusual discharges of electricity from the Sun through the medium of the inter-stellar ether. 28. THE QUESTION OP THE EXTINC- TION OF THE SUN. One other topic will suffice to close our present consideration of this sub- ject. It would certainly appear a very obvious conclusion to draw from the Sun's combustion, that the body must ultimately be consumed. A few propositions may dispel the error of this inference. The first proposi- tion is that all substances are inde- structible, and although matter may be changed in form or combination, yet the substance composing the mat- ter still remains in other forms or relations. This is also true of the Sun, and hence that body could be consumed only in the event that when its matter is being reduced to a gaseous or atomic state, and thrown THE SUN ; ITS CONSTITUTION, ETC. into the stnrotmding chromosphere or j Then, again, since it has oeen de- atmosphere, it should never return to j termined that heat, light and elec- the parent body. This would follow tricity are not substances, we have only in case the explosions we have described as taking place in its crust were quite constantly sufficient to project the ejected matter to such an no evidence of any continuous emis- sion of matter from the Sun beyond the sphere of its immediate attrac- tion, to other planets or Suns, and immense distance that the power of hence there is no drain upon it from attraction for the Sun would be only ! such a source, equal to the projectile force, which I becomes tangential, in which event the matter would not return to the parent body, but revolve in a circle which returns into itself; or if the matter were projected to such a dis- tance and in such direction as to intercept the stronger, because the more immediate, attraction of some We have seen that nearly all, if indeed not all, the matter which is ejected from the Sun through the Sun spots by explosions, or from its surface by radiation in the process of reduction,* enters into the atmos- phere where in its separate atomic state it is cooled off, thereby becom ing again subject to the power of other body, and be thus absorbed by j attraction, and by this force is re- it. That the matter which forms all ! turned to the photosphere where it the planets of this system may have been so ejected at different periods of time, Mercury and Vulcan at com- paratively recent periods, is not im- possible nor even improbable ; but even if this be true, it furnishes no resumes the process of condensation on the exterior and reduction in the interior of that bodv, BO that no mat- ter is lost from the Sun by this pro- cess. While, however, it is manifest that evidence of an ultimate destruction of j the matter of the Sun will never be that manner, as the Sun yet contains exhausted, it is quite as manifest that six hundred and ninety-eight seven- hundredths of all the matter in the Solar Universe, and its explosive power must have so greatly declined since the period when even the Earth was thrown off, that it will never be able to eject the immense percentage of matter which remains. It may be possible, and, indeed, some scientists maintain it as proba- ble, that pome matter is ejected from the Sun by these explosions with such force and in such forms that it reaches the Earth as well as other planets in the condition we call comets and meteoroids, and as such is absorbed. Yet even if this be also true, it furnishes no evidence of a final extinction of the Sun, for the reason that notwithstanding both these processes have been carried on for millions of years, yet but two seven hundredths of the matter has been discharged, and evidences of decreasing explosive power are rapid- ly multiplying. the time will come when the conden- sation of the matter forming its crust will so far outstrip the process of re- duction within, that the atoms of this crust will be in such a state of com- parative quietude as to be not only no longer self-luminous, but that thii quietude will become so complete that the body will no longer send forth its volume of heat, but be as cold as the earth, and as dead, as regards both light and heat, as is now the lifeless moon. Prof. Young estimates that the Sun has been thirty millions of years reaching its present condition, and that ten millions of years will elapse ere its light and heat are en- tirely extinct. * It is the vibratory motion of the heated matter emanating from the surface of the Sun, through the process of radiation, reduc- tion, or vaporization, as may be observed in a highly heated mass of iron, that gives to the photosphere the "mottled" appearance described by observers. THE SUN; ITS CONSTITUTION, ETC. APPENDIX. 1. THE SUN'S CORONA AND HIS SPOTS. (By Richard A. Proctor.)* One of the most important results of observations made upon the eclipse of July 29, 1878, indicates the exist- ence of a law of sympathy, so to speak, between the solar corona and the Sun-spots. The inquiry into this relation &eems to me likely to lead to R very interesting series of researches, from which may possibly result an interpretation not only of the rela- tion itself, should it be found really to exist, but of the mystery of the Sun- spot period. I speak of the Sun- spot period as mysterious, because even if we admit (which I think we cannot do) that the Sun-spots are produced in some way by the action of the planets upon the Sun, it would still remain altogether a mystery how this action operated. When all the known facts respecting the San-spots are carefully considered, no theory yet advanced respecting them seems at all satisfactory, while no approach even has been made to an explanation of their periodic increase and diminution in number. This seems to me one of the most interesting problems which astronomers have at present to deal with; nor do I despair of seeing it satisfactorily solved within no very long interval of time. Should the rec- ognition of a sympathy between the corona and the Sun-spots be satisfac- torily established, an important step in advance will have been made, possibly even the key to the enigma will be found to have been dis- covered. I propose now to consider, first, whether the evidence we have on this subject is sufficient, and afterward to discuss some of the ideas suggested by the relations which have been rec- ognized as existing between the Sun- * From his collection of Essays entitled Rough Ways Made Smooth." spots, the sierra, the colored promi- nences, and the zodiacal light. The evidence from the recent eclip- ses indicates beyond all possibility of doubt or question, that during the years when Sun-spots were numerous, m 1870 and 1871, the corona, at least on the days of the total olar eclipses in those years, presented an appear- ance entirely different from the coro- na seen on July 29, 1878, when the Sun was almost free from spots. This will be more fully indicated further on. At present it is necessary to no- tice only (1) that whereas in 1870 and 1871 the inner corona extended at least 250,000 miles from the Sun, it reached only to a height of some 70,- . 000 miles in 1878; (2) in 1870 and 1871 it possessed a very complicated structure, whereas in 1878 the definite structure could be recognized only in two parts of the inner corona; (3) in 1871 the corona was pink, whereas in 1878 it was pearly white; (4) the co- rona was ten times bnghter in 1871 than in 1878; lastly, in 1871 the light f the corona came in part from glow- ng gas, whereas in July, 1878, the ight came chiefly, if not wholly, from. Rowing solid or liquid matter. I must icre point out, that the evidence of change, however satisfactory in itself, ,vould be quite insufficient to estab- ish the general theory that the corona sympathizes with the solar photo- phere in the special manner suggested :>y the recent eclipse observations. There are few practices more unscien- tific, or more likely to lead to erro- neous theorizing, than that of basing general theory on a small number of observations. In this case we have, in fact, but a single observed correspondence, though the obser- vations establishing it form a series. It has been shown that so far as the special Sun-spot period from the min- imum of 1 867 to the minimum of 1878 is concerned, there has been a certain correspondence between the aspect of the corona and the state of the Sun's surface, with regard to spots. To assume from that single correspond- 30 THE SUN; ITS CONSTITUTION, ETC. ence that the corona and Sun-spots I that my purpose is to ascertain where are related in the r:mie way, would be j the truth lies. I shall neither iutro- hazardous in the extreme. We may duce any observation of the corona, indeed find, when we consider other | because it seems specially favorable matters, that the probability of a gen- j to the theory that the corona sympa- eral relation of this sort existing is so I thizes with the photosphere, nor omit great antecedently, that but slight any, because it seems definitely op- direct evidence would be required to establish the existence of the re- lation. But it must be remembered that before the eclipse of 1878 was observed, with the special result I posed to that theory. To prevent any possibility of being unconscious ly prejudiced, I shall take a series of coronal observations collected to- gether by myself, on account of their have noticed, few were bold enough | intrinsic interest, several years ago, to assert the probable existence of any such relationship ; and certainly no one asserted that the probability was very strong. I believe, indeed, that no one spoke more definitely in favor of the theory that the corona probably sympathizes with the Sun- spots than 1 did myself before the recent eclipse ; but certainly I should not then have been willing to say that I considered the evidence very strong. We must then look for evidence of a more satisfactory kind. Now, although dining the two cen- turies preceding the invention of the spectroscope and the initiation of the solar physical researches now in pro- gress, observations of eclipses were not very carefully conducted, yet we have some records of the appearance of the corona on different occasions, which, combined with the known law of Sun spot periodicity, may enable us to generalize more safely than we could from observations during the present spot period, though these ob- servations have been far more ex- act than the older one-;. I propose to examine some of these. Neces- sarily I must make some selection. I need ha r dly say that even if there were no such relation as that which seems to be indicated by recent ob- servations, and if my purpose were simply to prove, either that such a relation exists or that it does not, I could very readily bring before the reader of these pages what would seem like the most satisfactory evi- dence that the relation is real. I must ask him to believe, however, when I had not in my thoughts any theory respecting periodic changes in the corona the series, namely, which is included in the sixth chapter of my treatise on the Sun. Each of these observations I shall consider in con- nection with the known condition of the Sun as to spots, and those results which seem to bear clearly^ whether favorably or unfavorably, on the the- ory we "are inquiring into, I shall bring before the reader. Kepler, whose attention had been specially drawn to the subject of the light seen around the Sun during to- tal eclipse, by certain statements which Clavius had made respecting the eclipse of 1567, describes the eclipse of 1605 in the following terms: "The whole body of the Sun was completely covered for a short time, but around it there shone a brilliant light of a reddish hue and uniform breadth, which occupied a considerable portion of the heavens." The corona thus seen may fairly be assumed to have resembled in extent that of 1871. A bright corona, reach- ing like that seen during the eclipse of July, 1878, to a height of only about 70,000 miles from the Sun's surface, would certainly not have been described by Kepler as occupy- ing a considerable portion of the heavens, for a height of 70,000 miles would correspond only to about a twelfth of the Sun's diameter ; and a ring so narrow would be described very differently. It seems, then, that in 1605 a corona was seen which cor- responded with that observed when THE SUN; ITS CONSTITUTION, ETC 31 the Sun has had many spots on his surface. Now we have no record of the condition of the Sun with regard to spots in 1605 ; but we know that the year 1615 was one of many spots, and the year 1610 one of few spots ; whence we may conclude safely that the year 1605 was one of many spots. This case then is in favor of the theory we are examining. In passing we may ask whether the observation by Clavius which had perplexed Kepler, may not throw some light on our subject. Clavius says that the eclipse of 1567, which should have been total, was annular. The usual explanation of this has been that the corona was intensely bright close to the Sun. And though Kepler considered that his own ob servation of a broad reddish corona satisfactorily removed Clavius' s dif- ficulty, it seems tolerably clear that the corona seen by Clavius must have been very unlike the corona seen by Kepler. In fact, the former must have been like the corona seen in July, 1878, much smaller than the average, but correspondingly in- creased in luster. Now with regard to the Sun-spot period we can go back to the yeir 1567, though not quite so securely as we could wish. Taking the average Sun-spot period at eleven years, and calculating back from the minimum of spots in the year 1610, we get four years of minimum solar disturbance, 1599, 1588, 1577, and 1566. We should have obtained the same result if we had used the more exact period, eleven one ninth years, and had taken 1610.8 for the epoch of least solar disturbance (1610.8 meaning about the middle of Octo ber, 1610). Thus the year 1567 was a year of few Sun-spots, probably oc- cupying almost exactly the same po- sition in the Sun-spot period as the year 1878. Clavius's observation, then, is in favor of our theory. But another observation between Clavius's and Kepler's may here be noticed. Jensenius, who observed the eclipse of 1598 at Torgau in Ger- many, noticed that, at the time of mid- totality, a bright light shone round the moon. On this occasion, remarks Grant, the phenomenon was generally supposed to arise from a de- fect in the totality of the eclipse, though Kepler strenuously contended that such an explanation was at variance with the relation between the values of the apparent diameters of the Sun and Moon as computed for the time of the eclipse by aid of the solar and lunar tables. The corona, then, must have resembled that seen by Clavius, and since the year 1598 must have been very near the time of fewest spots, this observation accords with the theory we are examining. The next observation is that made by Wyberd during the eclipse of 1H52. Here, there is a difficulty arising from the strange way in which the Sun-spots behave 1 during the interval from 1645 to 1679. Ac- cording to M. Wolf, whose investi- gation of the subject has been very lose and searching, there wa^ a max- imum of Sm spots in 1639 followed by a minimum in 1645, the usual in- terval of about six years having elapsed ; but there came a maximum in 1655, ten years later, followed by a minimum in 1666, eleven years later, so that actually twenty-one years would seem to have elapsed be- tween successive minima (1645 and 1666). Then came a maximum in 1675, nine years later, and a mini- mum in 1679, four years later. Be- tween the maxima of 1639 and 1675, including two spot periods, an inter- val of thirty-six years elapsed There is no other instance on record, so far as I know, of so long an interval as this for two spot-periods. In pass- ing, I would notice how little this circumstance accords with tho theory that the Sun-spots follow an exact law, or that from observations of the Sun, means can ever be found for forming a trustworthy system of weather prediction, even if we as- sumed (which has always seemed to me a very daring assumption), that 32 THE SUN; ITS CONSTITUTION, ETC. terrestrial weather is directly depend- ent on the progress of the Sun-spot period. But here the irregularity of the spot changes affects us only as preventing us from determining or even from guessing what may have been the condition of the Sun's surface in the year 1652. This year followed by seven years a period of minimum disturbance, and preceded by three years a period of maximum disturb- ance ; but it would be unsafe to as- sume that the Sun's condition in 1652 was nearer that of maximum than that of minimum disturbance. We must pass over Wyberd's observa- tions of the corona in 1652, a* least until seme direct evidence as to the Sun's condition shall have been ob- tained from the papers or writings of the observers of that year. I note only that Wyberd saw a corona of very limited extent, having indeed a height not half so great as that of many prominences which have been observed during recent eclipses. If the theory we are examining should be established beyond dispute, we should be led to infer that the year 1652 was in reality a year of mini- mum solar disturbance. Perhaps by throwing in such a minimum between 1645 and 1666, with of course a cor- responding maximum, the wild irreg- ularity of the Sun spot changes be- tween 1645 and 1679 would be to some degree diminished. We are now approaching times when more satisfactory observations were made upon the corona, and when also we have more complete records of the aspect of the Sun's surface. In 1706 Plantade andCapies saw a bright ring of white light extending round the eclipsed Sun to a distance of about 85,000 miles, but merging into a fainter light, which extended no less than four degrees from the eclipsed Sun, fading off insensibly un- til its light was lost in the obscure background of the sky. This corre- sponds unmistakably with such a coro- na as we should expect only to see at a time of many Sun-spots, if the theory we are examining is sound. Turning o Wolf's lis r , we find that the year 1705 is marked as a year of maximum solar disturbance, and the year 1712 as that of the next minimum. There- Pore 1706 was a year of many Sun- spots in fact, 1706 may have been the year of actual maximum disturb- ance, for it is within the limits of doubt indicated by Wolf. Certainly a corona extending so far as that which Plantade and Capiessaw would imply an altogether exceptional de- gree of solar disturbance, if the theory we are considering is correct. In 1715 Halley gave the following description of the corona: "A few seconds before the Sun was all hid, there discovered itself round the Moon a luminous ring about a digit v (a twelfth) "or perhaps a tenth part of the Moon's diameter in breadth. It was of a pale whiteness or rather pearl color, seeming to me a little tinged with the colors of the Iris, and to be concentric with the Moon." He added that the ring appeared much whiter and brighter near the body of the Moon than at a distance from it. and that its exterior boundary was very ill-defined, seeming to be deter- mined only by the extreme rarity of the luminous matter. The French as- tronomer Louville gave a similar ac- count of the appearance of the ring. He added, however, that "there were interruptions in its brightness, causing it to resemble the radial glory with which painters encircle the heads of the saints." The smallness of the co- rona on this occasion corresponds with the description of the corona Rteii in July, 1878 ; and though Louville's de- scription of gaps is suggestive of a somewhat different aspect, yet, on the whole, the corona seen in 1715 more closely resembles one which would be seen at a time of minimum solar dis- turbance, if our theory can be trusted, than one which would be seen at a time of maximum disturbance. Wolfs list puts the year 1712 as one of min- imum disturbance, with one year of doubt either way, and the middle of THE SUN ; ITS CONSTITUTION, ETC. the year 1817 as the epoch of maxi- mum disturbance, with a similar range of uncertainty. The case, then, is doubtful, but on the whole inclines to being unfavorable. I may remark that because of its unfavorable nature, I depar ed from the rule I had set my- self, of taking only the cases included in my treatise on the Sun. For the corona of 1 7 15 is not,r! escribed in that treatise, as indeed affording no evi- dence respecting this solar appendage. The evidence given in this case isprob- ably affected in some degree by the unfavorable atmospheric conditions under which Halley certainly, and Louville probably, observed the eclipse. In any case the evidence is not ptiong; only I would call atten- tion here to the circumstance that if, as we proceed, we should come to a case iu which the evidence is plainly against the theory we are examining, we must give up the theory at once. For one case of discordance does more to destroy a theory respecting associ- ation between such and such phe- nomena, than a hundred cases of agreement would do iu the way of confirming it. In 1724, Maraldi noticed that the corona was broadest first on the side toward which the Moon was advanc- ing, and afterward on the side which the Moon was leaving. From this we may infer that the corona was only a narrow ring on that occasion, since otherwise the slight difference of breadth due to the Moon's eccentric position at the beginning and end of totality would not have been notice- able. Now, the year 1723 was one of minimum disturbance, with one year of doubt either way. Thus 1724 was certainl) a year of few Sun-spots, and may have been the actual year of minimum disturbance. The corona then presented an appearance accord- ing with the theory we are consider- ing. Few eclipses have been better ob- served than that of the year 1733. The Royal Society of Sweden invited all who could spare the time to assist, as far as their ability permitted, in recording the phenomena presented during totality. The pastor of Stona Malm states that at Catherinesholrn, there was a ring around the Sun about 70,OOP miles in hight. Of course these are not his exact words ; what he actually stated was that the ring was about a digit in breadth. This is the exact hight assigned to the coronal ring by the observers of the eclipse of last year. The ring seemed to be of a reddish color. Another clergyman, Vallerius, states also that the ring was of this color, but adds that at a considerable dis- tance from the Sun it had a greenish hue. This suggests the idea that the outer corona was seen also by Valle- rius, and that it had considerable breadth. The reddish color of the inner light portion would correspond to the color it would have if it con- sisted in the main of glowing hydro- gen. If that really was its constitu- tion, then the theory advanced by one observer of the last eclipse that at the time of minimum solar disturb- ance the glowing hydrogen is with drawn from the corona, would be shown to be incorrect; for 1733 w r as the actual year of minimum solar disturbance. The pastor of Smoland states that "during the total obscura- tion the edge of the Moon's disk resembled gilded brass, and the faint ring round it emitted rays in an up- ward as well as in a downward direc- tion, similar to those seen beneath the Sun when a shower of rain is impend- ing." The mathematical lecturer of the Academy of Charles-stadt, M. Edstrom, observed these rays with special attention. He says that "they plainly maintained the same position until they vanished along with the ring upon the re appearance of the Sun." On the other hand, at Lincopia no rays were seen. On the whole it seems clear from the ac- counts of this eclipse that the inner corona was bright and narrow; rays tssued from the outer faint ring; but ihey were very delicate phenomena, THE SUN; ITS CONSTITITIION, ETC. easily concealed by atmospheric haze and thus were not everywhere ob- served. As rays were seen in July, 1878, there is nothing in the evidence afforded by the eclipse of 1733, oc- curring at a time of fewlspots, which opposes itself definitely to the theory we are considering. But the reddish color of the corona as already noticed is a doubtful feature. In July, 1878, the bright inner corona was of a pearl color and luster. During the eclipse of February, 1766, the corona presented four lu- minous expansions, and seems to have presented a greater expansion than we should expect in a year of mini- mum solar disturbance. Such, how- ever, the year 1766 certainly was. The evidence in this case is unfavora- ble to our theory not quite deci sively so, but strongly. For we should expect that in the year of act- ual minimum disturbance the corona would be even narrower than in the year 1878, which was the year follow- ing that of least disturbance. And again, a strongly distinctive feature in the corona of July, 1878, was the absence of wide expansions, such as were seen in 1870 and 1871. Now if this peculiarity should really be at- tributed to the relation existing be- tween the corona and the Sun-spots, weshould infer that in 1 766 the corona would have been still more markedly uniform in shape. The existence of four well marked expansions on that occasion, forces us to assume that either the relation referred to has no real existence, or else that the corona may change from week to week as the condition of the Sun's surface changes, and that in February, 1766, the Sun was temporarily disturbed, though the year, as a whole, was one of minimum disturbance. But as the epoch of actual minimum was the middle of 176C, February 1766 should have been a time of very slight dis- turbance. I do not know of any ob- servations of the Sun recorded for the ' month of February, 1766. On the j whole, the eclipse of 1766 must be j regarded as throwing grave doubt on the relation assumed by our theory as existing between the corona and the Sun-spots ; and as tending to suggest that some wider law must be in question than the one we have been considering if any association really exists. The account given by Don An- tonio d'Ulloa of the appearance pre- sented by the corona during the total eclipse of 1778, is rendered doubtful by his reference to an apparent rota- tory motion of the normal rays. lie says that about five or six seconds after totality had begun, a brilliant luminous ring was seen around the dark body of the Moon. The ring became brighter as the middle of to- tality approached. " About the mid- dle of the eclipse, the breadth of the ring was equal to about a sixth of the Moon's diameter. There seemed to issue from it a great number of rays of unequal length, which could be discerned to a distance equal to the Moon's diameter." Then comes the part of d'Ulloa's description which seems difficult to accept. ' He says that ihe corona " seem e t j to be endued with a rapid rotatory motion, which caused it to resemble a fire- work turning round its center." The color of the light, he proceeds, '* was not uniform throughout the whole breadth of the ring. Toward the margin of the Moon's di k it appeared of a reddish hue; then it changed to a pale yellow, and from the middle to the outer border, the yellow gradually became fainter, until at length it seemed almost quite white." Setting aside the rays and their rotation, d'Ulloa's account of the inner corona may be accepted as satisfactory. The hight of this ring was, it seems, about 140,003 miles, or twice that of the ring seen in July 1878. As the year 1779 was one of maximum solar disturbance, there were doubtless many spots in 1778; and the aspect of the corona accorded well with the theory that the corona expands as the number of Sun-spots increases. THE SUN ; .ITS CONSTITUTION, ETC. We come now to three eclipses which are especially interesting as having been all carefully observed, some observers having seen all three, the eclipses, namely, of 1842, 1851, and 1860. Unfortunately, the eclipses of 1842 and 1851, occurred when the Sun-spots were neither at their greatest nor at their least degree of frequency. For a maximum of Sun-spots occurred in 1837, and a min- imum in 1844, so that 1842 was on what may be called the descending slope of a Sun-spot wave, nearer the hollow than the crest, but riot very near either: again, a maximum occurred in 1848, and a minimum in 1856, so that 1851 was also on the descending slope of a Sun spot wave, rather nearer the crest than the hollow, but one may fairly say about midway between them. Still it is essential in an inquiry of this sort to consider intermediate cases. We must not only apply the comparentia ad intellectum instartti- arum convenient ium, but also the comparentia instant iarum secundum magis ac minus. If the existence of great solar disturbances causes the corona to be greatly enlarged, as com- pared with the corona seen when the Sun shows no spots, we should expect to find the corona moderately en- larged only when the Sun shows a considerable but not the maximum number of spots. And again, it is conceivable that we may tiiid some noteworthy difference between the aspect of the corona when Sun-spots are diminishing in number, and its aspect when they are increasing. This point seems the more to need in- vestigation when we note that the evidence derived from eclipses occur- ring near the time either of maximum or of minimum solar disturbance has not been altogether satisfactory. It may be that we may find an explana- tion of the discrepancies we have re- cognized, in some distinction between the state of the corona when spots are increasing and when they are dimin- ishing in number. It is noteworthy that several care- ful observers of the corona in 1842 believed that they could recognize motion in the coronal rays. Francis Bail 7 compared the appearance .of tho corona to the flickering light of a gas illumination. O. Struve also was much struck by the appear- ance of violent agitation in the light of the ring. It seems probable that the appearance was due to move- ments in that part of our atmosphere through which the corona was ob- served. The extent of the corona was variously estimated by different observers. Petit, at Montpeliei, as- signed to it a breadth corresponding to a highth of about 200 OOJ miles; Baily a hight of about 509,030 miles; and O. Struve a eight of more than 800.000 miles. The last-named ob- server also recognized luminous ex- pansions extending fully four degrees (corresponding to nearly seven million miles) from the Sun. Picozzi, at Mi- lan, noticed two jets of light, which were seen also by observers in France. Rays also were seen by Mauvais at Perpignan, and by Baily at Paria. But Airy, observing the corona from the Superga, could see no radiation. He says "although a slight radiation might have been perceptible, it was not sufficiently intense to affect in a sensible degree the annular structure by which the luminous appearance was plainly distinguished." These varieties in the aspect of the corona were doubtless due to varieties in the condition of the atmosphere through which the corona was seen. Now it cannot be questioned that, so far as extension is concerned, the corona seen in 1842 was one which, if the theory we are considering were sound, we should expect to see near the time of maximum rather than of minimum solar disturbance. On the other hand, in brightness the corona of 1842, re- sembled, if it did not surpass, that of July 1878. U I had imagined," says Baily, "that the corona, as to its brilliant or lumin- ous appearance, would not be greater 36 THE SUK; ITS CONSTITUTION, ETC. than that faint crepuscular light which sometimes takes place (sic) in a sum- mer evening, and that it would encir- cle the Moon like a ring. I was there- fore somewhat surprised and aston- ished at the splendid scene which now BO suddenly burst upon my view." The light of the corona was so bright, O. Struve states, that the naked eye could scarcely endure it; "many could not believe, indeed, that the eclipse was total, so strongly did the corona's light resemble direct sun- light." Thus while as to extent the corona in 1842 presented the appear- ance to be exnected at the time of maximum solar disturbance, if our theory is sound, its brightness was that corresponding to a time of mini- mum disturbance. Its structure cor- responded with the former condition. The light of the corona was not uni- form, nor merely marked by radia- tions, but in several places interlacing lines of light could be seen. Arago, at Perpignan, observed with the un- aided eye a region of the corona where the structure was as of inter- twined jets giving an appearance reppinbling a hank of thread in dis- order. Certainly, for an eclipse occurring two years from the time of minimum, and live years from the time of maxi- mum disturbance, that of July, 1842,* has not supplied evidence favoring the theory with which we started. Whether any other theory of asso- ciation between the corona and the Sun- spots will better accord with the * 1 he actual condition of the .**un in 1842 may be infeired from the following table, showing the number of spots observed in 1837 the preceding year of maximum dis- turbance, in 184U, and in 1844 the following year of minimum disturbance ; the observer \vas fcchwabe of Dessau : Days of Days without New groups obst rvation. spots. obst rvtd. 1837 . 168 333 1842 . 307 64 68 1844 .321 111 62 Only it should be noticed that nearly all the spots seen in the year 1844 belonged to the next period, the time of actual minimum oc- curring earlv ;n 1844. evidence hitherto collected remains to be seen. Turn we now to the eclipse of 1851, occurring nearly midway between the epoch- of maximum solar disturbance (1848) and minimum solar disturb- ance (1856). I take the account given by Airy, our government astronomer, as he was one of the observers of the eclipse of 1842. " The corona was far broader," he says, "than that which I saw in 1842. Roughly speaking, the breadth was little less than the Moon's diameter, but its outline was very irregular. I did not notice any beams project- ing from it which deserved notice as much more conspicuous than the others; but the whole was beamy, radiated in structure, and termi- nated though very indefinitely in a way which reminded me of the ornament frequently placed round ;> mariner's compass. Its color was white, or resembling that of Venus. I saw no flickering or unsteadiness of light. It was not separated fiom the Moon by any interval, nor ha 1 it any annular structure. It looked like a radiated luminous cloud behind the Moon." The corona thus described belongs to that which our theory associates with the period of maximum rather than of minimum solar disturbance. Definite peculiarities of structure seem to have been more numerous and better marked than in 1842. It accords with our theory that 1851 was a year of greater solar disturb- ance than was observed in 1842, as the following numbers show: Days of Days without New groups observation. spots. obs rvtd. 1842 .317 64 68 1851 . 308 141 1860 . 332 211 I have included the year 1860, as we now proceed to consider the corona then seen by Airy. The year 1860 did not differ very markedly, it will be observed, from 1851, at regards the number of new groups af spots observed by Schwabe, especially when THE SUN; ITS CONSTITUTION, ETC. 37 account is taken of the number of days in which the Sun was observed in these two years. But 1 860 was a year of maximum solar disturbance, whereas 1851 was not.* Airy rein arks of the corona in 1860 : "It gave a considerable body, but I lid not remark either by eye-view or by telescope view anything- annular in its structure ; it appeared to me to resemble, with some irregularities (as I stated in 1851), the ornament round a compass card." Bruhns of Leipsic noted that the corona shone with an intense white light, so lustrous as to dim the pro- tuberances. He noticed that a ray shot out to a distance of abou^ one degree indicating a distance of at least 1,500,000 miles from the Sun's surface. This was unquestionably a coronal appendage as neither the di- rection nor the length of the ray va- ried for ten seconds, during which Bruhns directed his attention to it. Its light was considerably feebler than that of the corona, which was of a glowing white, and seemed to co- ruscate or twinkle. Bruhns assigned to the inner corona a height varying from abont 40,000 to about 80,000 miles. But this was unquestionably far short of the true height. In fact, Secchi's photographs show the corona extending to a distance of at least 175,000 miles from the surface of the Sun. Therefore probably what Bruhns calls the base of the corona was in reality only the prominence * The following table shows the position occupied by the years 1851 and 1860 in this report, as com pared with the year 1848 (max- imum next preceding 1851), 18- f i6 (minimum next following 1851) and 1867, minimum next following 1860 : 1848 1851 1856 1860 1867 Days of Days without observation. spots. 278 321 332 312 193 195 New groups observed. 930 141 34 211 25 A comparison of the three tables given in these notes and the text will afford some idea of the irregularities existing in the various waves of Sun-spots. region, and the inner corona was that which he describes as varying in breadth or height from nearly one- half to a quarter of a degree that ia from about 800,000 to about 400,000 miles. De la Rue gives a somewhat similar general description of the co- rona seen in 1 860. Pie remarks that it was extremely bright near the Moon's body, and of a silvery white- ness. The picture of the corona by Feilitsch (given at page 343 of my book on the Sun) accords with these descriptions. On the whole, the eclipse of 1860 affords evidence according well with the theory we have been considering, except as regards the brightness and the color of the corona, which corres- pond more closely with what was observed in July, 1878, with the lus- ter and color of the corona in 1870 and 1871. In this respect, it is sin- gular that the eclipse of 1867, which occurred (see preceding note) when the Sun-spots were fewer in number, presented a decided contrast to that of 1860, the contrast being, how- ever, precisely the reverse of that which our theory would require, if the color and brightness of the co- rona be considered essential features of any law of association. Herr Grosch, decribing the corona of 1867, says, "There appeared around the Moon a reddish glimmer- ing light similar to that of tho aurora, and almost simultaneously with this, (I mean very shortly after It) the co- rona." It is clear, however, from what follows, that tho reddish light was what is now corumonly called the inner corona, wnioh in July, 1878, when the Sun was m almost exactly the same condition as regards the spots, was peariy white and intensely bright. "T'ais reddish glimmer," he proceeds, " which surrounded the Moon with a border of the breadth of at most live minutes " (about 140,000 miles) u was not sharply bounded in any part, but was extremely diffused and less distinct in the neighborhood of the poles.'' Of the outer corona, 3ft THE SUN; ITS CONSTITUTION, ETC. he remarks that " its apparent height amounted to about 280,000 miles op- posite the solar poles, but opposite the eolar equator to about 670.000 miles. Its light was white. This white light was not in the least ra- diated itself, but it had the appear- ance of rays penetrating through it ; or rather as if rays ran over it, forming symmetrical pencils diverg- ing outward, and passing far beyond the boundary of the white light. These rays had a more bluish appear- ance, and might best be compared to those produced by a great electro- magnetic light. Their similarity to these, indeed, was so striking, that under other circumstances I "should have taken them for such, shining at a great distance. The view of the corona I have described is that seen with the naked eye. . . In the white light of the corona, close upon the Moon's edge, there appeared sev- eral dark curves. They were sym- metrically arched toward the east and west, sharply drawn, and re- sembling in tint lines drawn with a lead pencil upon white paper. . . Beginning at a distance of one min ute (about 26,000 miles), they could be traced up to a distance of about nine minutes (some 236,000 miles) from the Moon's edge." Almost all the features observed in this case correspond closely with those noted and photographed during the eclipse of December, 1871. In other words, the corona seen in 1867, when the Sun was passing through the period of least solar disturbance, closely resembled the corona seen in J871, when the Sun was nearly in its stage of greatest disturbance. Even the spectroscopic evidence obtained in 1871 and July, 1878, maybe so ex- tended as to show with extre.ne probability what would have been seen in 1867 if spectroscopic analysis had then been applied. We cannot doubt that the reddish inner corona, extending to a height of about 140,000 miles, would have been found under Bpectroscopic analysis to shine in part with the light of glowing hydrogen, as the reddish corona of 1871 did. The white corona of July, 1878, on the contrary, shone only with such light as comes from glowing solid or liquid matter. Here then, again, the evidence is unfavorable to our theory; for the corona in 1867 should have closely resembled the corona of 1878, if this theory were sound. It would be idle, I think, to seek for farther evidence cither in favor of the theory we originally proposed to discuss, or against it: for the evi- dence of the eclipse of 1867 disposes finally of the theory in that form. I may note in passing that the eclipse of 1868 gave evidence almost equally unfa'vorable to the theory, while the evidence given by the eclipse of 1869 was neutral. It will be desirable, however, to consider, before conclud- ing our inquiry, the evidence obtained in 1871 and in 1878, in order that we mny see what, after all, that evi- dence may be regarded as fairly prov- ing with regard to coronal variations. First, however, as 1 have consid- ered t\vo eclipses which occurred when the Sun spots were decreasing in number namely, thcae of 1842 and 1851, midway (roughly speaking) between the crest and hollow of the Sun-spot waveon its descending slope, it may be well to consider an eclipse which was similarly sit-iated with re- spect to the ascending slope of a Sun- spot wave. I take, then, the eclipse of 1858, as seen in Brazil by Liais. The picture drawn by this observer is one of the most remarkable views of the corona ever obtained. It is given at page 339 of my book on the Sun. Formerly it was the custom to deride this drawing, but since the eclipse of 1871, when the corona was photographed, it has been admitted that Liais's drawing may be accepted as thoroughly trustworthy. It shows a wonderfully complex corona, like that of 1871, extending some 700,- 000 miles from the Sun, and corres- ponding in all respects with such a corona as our theory (if established) THE SUN; ITS CONSTITUTION, ETC. would have associated with the stage of maximum solar disturbance. As in this respect the eclipse of 1858, when Sun spots were increasing, re- sembled those of 1842 and 1851> when Sun-spots were diminishing in number, we find no trace of any law of association depending on the rate of increase or diminution of solar disturbance. If we limited our attention to the eclipses of 1871 and of July, 1878, we should unquestionably be led to adopt the belief that the corona dur- ing a year of many spots differs mark- edly from the corona when the Sun shows few spots, or none. So far as the aspect of the corona is concerned, I take the description given by the same observer in both cases, as the comparison is thus freed as far as pos- sible from the effect of personal dif- ferences. Mr. Lockyer recognized in 1871 a corona resembling a star-like decora- tion, with its rays arranged almost symmetrically three above and three below two dark spaces or rifts at the extremity of a horizontal diameter. The rays were built up of innumera- ble bright lines of different length, with more or less dark spaces between them. Near the Sun this structure was lost in the brightness qf the cen- tral ring, or inner corona. In the tel- escope he saw thousands of interlac- ing filaments, varying in intensity. The rays so definite to the eye were not seen in the telescope. The com- plex structure of interlacing filaments could be traced only to a height of some five or six minutes (from 135,- 000 to 165,000 miles) from the Sun, there dying out suddenly. The spec- troscope showed that the inner co- rona, to this height at least (butRespi- ghi's spectroscopic observations prove the same for a much greater distance from the Sun), was formed in part of glowing gas hydrogen and the vapor of some as yet undetermined substance, shining with light of a green tint, corresponding to 1474 of Kirchhoff's scale. But also a part of the coronal light came from matter which reflected sunlight; for its spec- trum was the rainbow-tinted streak crossed by dark lines, which we ob- tain from any object illuminated by the Sun's rays. Ifc should be added that the photographs of the corona in 1871 show the three great rays above and three below, forming tho appear- ance as of a star-like decoration, de- scribed by Mr. Lockyer; insomuch as it is rather strange to find Mr. Lock- yer remarking that "the difference between the photographic and the visible corona came out strongly, . . .. and the non solar origin of the radial structure was conclusively estab- lished." The resemblance is, indeed, not indicated in the rough copy of the photographs which illustrates Mr. Lockyer's paper; but it is clearly seen in the photographs themselves, and in the fine engraving which has been farmed from them for the illus- tration of the volume which the As- tronomical Society proposes to issue ^some time in the present century, perhixps). Now in July, 1878, the corona pre- sented an entirely different appear- ance. Mr. Lockyer, in a telegram sent to the J)aity News, describes it as small, of pearly luster, and having indications of definite structure in two places only. Several long rays were seen ; but the inner corona was estimated as extending to a height of about 70,000 miles from the Sim's surface. The most remarkable change, however, was that which had taken place in the character of the corona's spectrum or, in other words, in the physical structure of the corona. The bright lines or bright images of the inner corona, according as it was examined through a slit or without one, were not seen in July, 1878, showing that no part, or at least no appreciable part, of its light came from glowing gaseous matter. But also the dark lines seen by Janssen in 1871 were wanting on this occasion, showing that the corona did not shine appreciably by reflect- 40 THE SUN; ITS CONSTITUTION, ETC. ing sunlight, The spectrum was, in fine, a continuous rainbow-tinted streak, such as that given by glowing solid or liquid matter. The inference clearly is, 1. That in July, 1878, the gaseous matter which had been present in the corona in 1871 was either entirely absent or greatly reduced in quantity; 2. The particles of solid or liquid, but, proba- bly, solid matter which, by reflecting sunlight, produced a considerable por- tion of the corona's light in 1871, were glowing with heat in July, It remains to be considered how science may hope to obtain more trustworthy evidence than we yet have respecting the corona and its changes of form, extent, luster, and physical constitution. In the case of the prominences, we have the means of making systematic observations on every fine, clear day. It has been, indeed, through observations thus effected by the spectroscopic method that an association has been m-o^ nized between the number, size, ami brilliancy of the prominences on the 1878, and shone in the main with this'one hand, and the number, size and inherent light ; and 8. The entire co- rona was greatly reduced in size in July, 1878, as compared with that which formed the "starlike decora- tion ' ' around the black body of the Moon in December, 1871 We cannot, however, accept the theory that such a corona as wasj other time. Of course, without the seen in 1871 invariably surrounds the aid of the spectroscope the corona, as Sun in years of great, disturbance, 'ordinarily seen during total eclipses. while the corona of July, 1873, is [must be entirely invisible when the the typical corona for years of small Sun is shining in full splendor. No activity of the Sun-spots on the other. But in the case of the corona we are as yet unable to make any observa- tions except at the time of total solar eclipse. It seems almost impossible to hope that any means can be de- for seeincr the corona at any solar disturbance. The generalization is flatly contradicted by the evidence which I have presented in the preced ing pages. It may be that such a corona as was seen in 1871 is com- mon in years of great disturbance just as spots are then more common, though not always present; while such a corona as was seen in July, 1878, is more common in years of small disturbance, just as days when the Sun is wholly without spots are then more common, though from time to time several spots, and some- times very large spots, are seen in such years. On the whole, I think the evidence I have collected favors rather strongly the inference that an association of this sort really exists between the corona and the Sun-spots. It would, however, be unsafe at pres- ent to generalize even to this extent ; while certainly the wide generaliza tion telegraphed to Europe from America as the great result of the eclipse observations in July, 1878, must unhesitatingly be rejected. one acquainted with even the merest elements of optics could hope to see the corona with an ordinary telescope at such a time. The spectroscope, again, would not help in the slight jst degree to show such a corona as was shhung in July, 1878; for the power of the spectroscope to show objects which under ordinary conditions are invisible, depends on the separation of rays of certain tints from the rays of all the colors of the rainbow, which make up solar light; and as the co- rona in July, 1878, shone with all the colors of the rainbow, and not with certain special tints, the power of the spectroscope would be thrown away on a corona of that kind. All that wo can ever hope to do is to discern the gaseous corona when, as in 1871, it is well developed, by spectroscopic appliances more effective for that purpose than any which have hith- erto been adoptedfor all which have as yet been adopted have, failed. Now, the difficulty of the problem 11 be recognized when we remem- THE SUN; ITS CONSTITUTION, ETC. 41 ber that the strongest tints of the corona' B light the green tint classi- fied as 1474 Kirchhoff has been specialty but ineffectually searched for in the Sun's neighborhood with the most powerful spectroscopic appli ances yet employed in the study of the colored prominences. In other words, when the light of our own air over the region occupied by the corona has been diluted as far as pos- sible by spectroscopic contrivances, the strongest of the special coronal tints has yet failed to show through the diluted spectrum of the sky. Again, we have even stronger evi- dence of the difficulty of the task in the spectroscopic observations made by Respighi during the eclipse of 1871. The instrument, or I should rather, perhaps, say the arrangement, which during mid totality showed the green image of the corona to a height of about 280 000 miles, did not show any green ring at all at the beginning of totality. In other words, so faint ia the light of the gaseous corona, even at its brightest part, close to the Sun, that the faint residual atmos- pheric light which illuminates the sky over the eclipsed Sun at the be- ginning of totality sufficed to oblite- rate this part of the coronal light. Whether with any combination specially directed to meet the difficul- ties of this observation, the gaseous corona can be rendered discernible, remains to be seen. I must confess my own hopes that the problem will ever be successfully dealt with are very slight, though not absolutely evanescent. It seems to me barely possible that the problem might be successfully attacked in the following way. Using a telescope of small size, for the larger the telescope the fainter is the image (because of great- er loss of light by absorption,) let the image of the Sun be received in a small, perfectly darkened came r a at- tached to the eye-end of the telescope. Now, if the image of the Sun were received on a smooth, white surface, we know that the prominences and the corona would not be visible. | And again, if the part of such a sur- face on which the image of the Sun itself fell, were exactly removed, we know (the experiment has been tried by Airy) that the prominences would not be seen on the ring of white sur- face left after such excision. Still less, then, would the much fainter image of the corona be seen. But, if 'this ring of white surface, illu minated in reality by the sky, by the ring of prominences and sierra, and by the corona, were examined through a battery of prisms (used without a slit) adjusted to any one of the known prominence tints, the ring of prom- inences and sierra would be seen in that special tint. If the battery . of prisms were sufficiently effective, and the tint were one of the hydro- gen tints, preferably, perhaps, the red we might possibly be able to trace the faint image of the corona in that tint. But we should have a better chance with the green tint cor- responding to the spectral line 1474 Kirchhoff. If the ring of white sur- face were replaced by a ring of green surface, the tint being as nearly that of 1474 Kirchhoff as possible, the chance of seeing the coronal ring in that tint would be somewhat in- reased ; and, still further, perhaps, if the field of view were examined through green glass of the same tint. It seems just possible that if prisms of triple height were used, through which the rays were carried three times, by an obvious modification of the usual arrangement for altering the level of the rays, thus giving a power of eighteen flint glass prisms of ;ixty degrees each, evidence, though slight perhaps, might be ob- tained of the presence of the sub- stance which produces the green line. Thus, variations in the con- . dition of the corona might be recog- nized, and any law affecting such variations might be detected. I must confess, however, that a consider- ation of the optical relations involved n the problem, leads me to regard THE SUN; ITS CONSTITUTION, ETC. the attempt to recognize any traces of the corona when the Sun is not eclipsed, as almost hopeless. It is clear that until some method for thus observing the corona has been devised, future eclipse observa- tions will acquire a now interest from the light which they may throw on the coronal variations, and their pos- sible association in some way, not as yet detected, with the Sun-spot period. Even when a method has been de- vised for observing the gaseous co- rona, the corona whose light comes either directly or by reflection from solid or liquid matter will still remain undiscernible save only during total eclipses of the Sun. Many years must doubtless pass, then, before the relation of the corona to the promi- nences and the Sun spots shall be fully recognized. But there can be no question that the solution of this problem will be well worth waiting for, even though it should not lead up (as it most probably will) to the solu- tion of the mystery of the periodic changes which affect the surface of the sun. II. THE FUEL OP THE SUN.* Mr.Williams's essay opens with the argument that Wollaston was wrong in regarding the atmospheres of the earth and other members of the solar system as limited. Mr. Williams at- taches great importance to this point, considering that if he is right, all our standard treatises on pneumatics and more years than have passed binct Mr. Williams's theory was advanced, is incoEsistent with Wollaston's opin- ion, and 6 till more obviously with the reasoning by which Wollaston at tempts to establish his opinion. The rather daring theory of Lu Sage at to the true cause of gravitation may be cited as an illustration of what is undoubtedly the case, that many be- fore Mr. Williams have regarded in- terplanetary and interstellar space as occupied by matter. As for the consequences of the opinion maintained by Mr. Williams (most probably right), he is, I take it, quite mistaken in supposing them to be of great importance. lie finds the objections urged against his views, and Dr. Siemens's later ones, invalid when once the atmospheres of the heavenly bodies are regarded as unlimited. I have myself received more than one letter pointing out that this is so. Dr. Siemens himself is of course persuaded that it is. Hut the argument is based on the mis- taken idea that because there is no definite limit to a planet's atmos- phere (or if there is no such limit), the atmosphere which at any instant envelopes a planet is freely inter- changeable with the interplanetary atmosphere. But this would not be the case. Interchange could only take place in accordance with dy- namical laws, and these would not permit of more than an infinitesimal interchange between the atmosphere immediately surrounding a planet meteorology must be remodeled. 1 1 and the attenuated atmosphere be- yond. Mr. Williams recognizes this cannot, for my own part, see why. I doubt very much whether Dr. Wol- laston's paper has ever been h* Id to be of great importance, or whether it has as soon as he tries to set his perpetual solar machine working. "The Sun will carry its own special atmospheric * . i * l .* I . ever been regarded as demonstrated ; matter with it, but it cannot carry the that the planetary atmospheres are j whole of the interstellar medium. limited. Certainly the atomic theory, , There must be a limit graduated, no as it has been maintained for many! doubt, but still a practical limit at - j which its own atmosphere will leave . . azin "Knowledge.'; November 3 18 *From T*. A. Proctor's scientific magazine, behind, or pass through, the general 'Ihe atm ospheric matter." This ad mis- ^\^^ though convenient where it i. made, carries death with it to Mr. HUMBOLDT LIBRARY, No 4 1. THE SUN; ITS CONSTITUTION, ETC. 43 Williams's theory, for it leaves things praciically as they would be if Mr. Wollaston's theory were unques- tioned. Mr. Williams conceives the Sun as rushing along through space, gather- ing in the atmosphere of space as it goes, compressing that atmosphere with all the energy with which a normally limited atmosphere would be permanently compressed, and so by its gravitating energy producing intense heat, instead of th.it merely constant pressure which would natu- rally result in the case of a constant atmosphere. But neither the onward rush of the Sun through space, nor that swaying of the Sun around the common center of gravity of the solar system, which Mr. Williams regards as an all-important point in his theory, could produce any such effect. If we imagine the Sun with- out his atmosphere, drawing that at- mosphere in from surrounding space, he would unquestionably, in drawing it in, produce all the heat in which Mr. Williams believes. And that heat might be stowed away, so to speak, iti dissociating the aqueous vapor so gathered in, to be presently distributed as the elements recom- bined. But with that first ingather- ing of atmosphere would be the end of this particular source of solar heat. The heat thus stored could be given out, but no more, or only so much more as corresponded to the exceedingly slight interchange taking place at the outskirts of the solar atmosphere Mr. Williams speaks as if the whole of the long cylinder of interstellar atmosphere actually tra- versed by the Sun were gathered in and compressed to the full tension of the solar atmosphere. But this could not happen The Sun would travel through that atmosphere, losing from his own (and taking up from outside to replace) only so much as friction at the outskirts of his atmosphere would displace. If there could be any doubt, when the question is viewed as a hydrody- riarnical problem, that this is so, it should be removed by the considera- tion that were the processes con- ceived by Mr. Williams to take place, one side of the sun would in- evitably present an appearance differ- ing in the most striking manner from that of the other side. On the for- ward hemisphere, there would occur a constant ingathering of so much atmosphere as, when compressed by solar attraction, would produoa the heat which Mr. Williams' 3 theory requires for note that the mere state of compression does not caus3 heat, but only the forcible compression of vaporous matter which had been un- compressed. All the heat thus gen- erated on one side would be used up in dissociating the aqueous vapor of the atmosphere so gathered up. On the other hemisphere the converse process would be taking place. The dissociated gases would there rise, would combine, with intense emission of heat, an i the products the cin- ders left after the solar firing would be flung away in the wake of the advancing Sun. At least Mr. Wii- iams's theory requires that this ihould happen. Now, astronomers lave the power of observing at one season of the year the advancing side of the Sun, and six months later the retreating side; and they might fairly xpect that regions where such oppo- site processes are at work on so gi- antic a scale would present a very ifferent appearance. But no one ias ever yet recognized the slightest difference between the side where the Sun is, as it' were, shovelling in fuel turned towards the Eanh during the spring of the northern hemi- sphere and the other side where he is shovelling out cinders. Both sides look exactly alike. There is another feature of Mr. Williams's theory which he specially defends against criticisms of mine. I had objected that bodies traveling around the Sun could never have come into existence as a result of ejections from the Sun. Granted, 44 THE Sl r N'; ITS CONSTITliriON, ETC. says Mr. Williams though that was ncTt exactly the way lie put it in "The Fuel of the Sun," I think if there were only simple ejections; but if, after matter has been ejected, it explodes like a rocket, "pretty generally all around," a ring of me- teors might be formed ; and he cites the behavior of the colored promi- nences of the Sun as showing that this actually happens. It is true they often, after shooting up from the Sun's surface, expand laterally, but there is nothing in this more than we see in every case in which gaseous matter is shot through a region of high pressure into * region of low pressure. The mauer shot to a height of pay 70,000 miles from the Sun's surface, should there explode laterally, so as thenceforward to cir- cle around him, the matter exploding must divide itself into opposite por- tions, each traveling from the point of explosion with a velocity of more than 240 miles per second. Nothing of this sort, cr approaching anywhere near this, has ever been seen. Moreover, what is there except expansive action to produce lateral motion at all in the ejected gases? and how can lateral expansion do more than extend the expanding matter until its density is equal to that of the atmosphere around it at the same level? In the case of terrestrial bomb-rockets there is an enclosing case which holds the explosive sub- stance until, on ignition, the gases are formed which, by their expan- sive action, drive out the particles of matter which form the luminous dis- play. The circumstances are there- fore favorable to the forcible expul- sion of matter. It is different in the case of the gaseous matter expelled from the Sun, when the outrush is over. For the glowing gas driven violently outward on these occasions, is not enclosed in any way. It is sim- ply (as the spectroscope shows) driven up as a stream of dense gas in a relatively rare atmosphere ; and as FOOU as it can (which is generally not before it reaches a higher and still rarer atmosphere; it expands lat- erally. There is nothing explosive about this action, any more than there is in the lateral expansion of cumulus clouds, or (which more nearly illus- trates the case) in the outspread of cloud above a volcano after each out- burst of the gases which had been imprisone'd within. If there were the enormous lateral velocities required by Mr. Williams's theory, the spec- itroscope would long ere this have re- vealedthem; butwhile it gives clear evidence of cyclones low down in the solar atmosphere, as ehown by mo tions toward and from the eyo at th- Sun's edge, it has never shown any trace of such motions in the glowing gas flung high above the Sun's sur- face. There is, however, much that is well worth studying in Mr. Williams's reasoning. His conclusions seem to me, for the most part, quite erroneous, but the evidence he quotes in their favor is deserving of the most careful examination. Mr. Williams considers that his views have been and are being adopted by other writers on astro- nomical and physical matters, " with- out corresponding acknowledgment"; and he tells us that in duo time "an appendix to the 'Fu-.l of the Sun'*' will be published (to a new edition. I trust), giving the particulars of such adoption. I doubt the wisdom of this. These questions of priority are lit only to occupy very small minds ; and I am sure Mr. Williams agrees with me in regarding all egotism as silly : even the appear- ance of it is a thing to be avoided. But if lie does what he proposes, he will have to be careful lest peradven- ture he should lind the boot unmis- takably on the other leg. lie has a clear case against Dr. Siemens, though I feel well assured Dr. Sie- mens was not aware, when he pub- lished his theory, how fully all that was sound in it, and a great deal also THE SUN; ITS CONSTITUTION, ETC. that is unround, had been anticipated by Mr. Williams. But in some other cases, where he hints a suspi cion that his views have been adopted without acknowledgment, he willn'nd priority ( valeat quantum valere debit, which is not saying much) with others. For instance, the theory that the larger placets are miniature suns, "surrounded by a sphere of vapor, the outside of which we see," he in- cludes among his startling conclu- sions, "utterly at variance with gen eral astronomical opinion when lie reached them." When he reached them I do not know, but I do know when he published them ; and I know- that several months before, in the winter of 1869, 1 advanced that theory in a series of lectures delivered at the Royal Institution, Manchester (in the | position of its essential points; svliabus of which the theory wsis cinnot believe either that I a stated in so many words), while for at least \\ ye~ar before that, the prob- ably intensely-heated condition of the giant planets had been dealt with in the MS. of the work afterward published under the title of "Other Worlds than Ours." Mr. Williams could not be expected to know about the Manchester lectures, but he must know enough of the conditions under which books are published to be well aware that the chapters on the giant planets in the middle of that work were written, and even in type, before his -'Fnel of the Sun " was published. The theory was announced by me long before. Not that it mat ters in the least, only : if such ques- tions are to be raised, we rmw as well raise them by the right tint III. THE FUEL, OF THE SUN.* A Reply, by W. M. Williams. I must ask leave to correct Mr. Proctor's total misapprehension of my theory when he describes me as sup- posing that the Sun, after having ob- tained his gravitation equivalent of * From ' Knowledge," I^uv. 1O, Ioo2, the universal atmospheric matter, generates more heat by merely com- pressing on one side and rarefying on the other the same unaltered kind of matter. This would be quite on a level with the customary paradox of the perpetual motioners, and closely resembling what or.e would get by a pair of reciprocating pistons com- pressing the air of one cylinder by the elastic expansion of the other. Mr. Proctor correctly represents my view of the effects of the original aggregation and condensation of at- mospheric matter about the Sun ; but as regards my attempt to solve the great problem of the maintenance 01 solar energy, he has not even crossed the threshold of the argument, and has evidently "taken as read" inyex- for I am inca- pable of explaining, or he of under- standing, what I intended to ex- pound. The threshold of the argument to which I allude, and at which Mr Proctor halts, is that the heat e* olved by this origin il .aggregation and corn pression would dissociate the atmos- pheric compounds (notably water va- por), and thereby store a reservoir of heat ; but beyond this, I have shown that the recombination and explosion of the whole of this is restrained by the limitation of radiation due to the "jacket" or envelope of the chroma- tosphere and outer atmosphere of the Sun ; this limitation determining the depth of the photosphere, or amount of surface combustion or recombina- tion. Mr. Proctor has not penetrated even this, the vestibule of the argu- ment. A step further brings us to that "swaying of the Sun around the cen- ter of gravity of the solar system which Mr. Williams regards as an all- important point of his theory," and of which point Mr. Proctor altogether fails to grasp the significance. I maintain that this produces the ir- regular angular or rotatory velocities of the different portions of the solar 46 THE SUN; ITS CONSTITUTION, ETC. photosphere which Carrington de- monstrated (the equatorial portions making a complete revolution in { 30 86 days, while those in latitude of about 5U revolve in 28-30 days), and that such irregularity, presuma- bly shared by the outer vapor jacket, must produce vortices or cyclones on and about both bordei s of the equa- torial solar zone; that these vortices must rip open that jacket thereabouts, and thus remove the restraint to com- bustion in such spots. The conse quence of this (as demonstrated by the laboratory researches of Deville, Bunsen, and others) must be explosive outburts in the trail of these vortices of a magnitude corresponding to themselves. This ripping open of the solar integuments, and conse- quent ejection of his dissociated en- trails, is what we observe in the spots and prominences. But what must follow the forma tion of this partial and local vacuum produced by such ejection? Evidently an inrush to restore the broken equi librium of general gaseous pressure. I need scarcely work out the pro- gressive steps of this restoration, first from the contiguous gaseous matter, then from the further distant, and finally from & portion of that cylin- der of interstellar atmospheric matter which by the solar translation in space is (as I m SECTION XXV. PERIODICITY OF THE SPOTS ........ 23 SECTION XXVI. THE SPOTS ARE CAVITIES IN THE SUN, . . . ; . 24 SECTION XXVII. How THE HEAT OF THE SUN REACHES THE EARTH, . . 25 SECTION XXVIII. I'HE QUESTION OF THE EXTINCTION OF THE SUN, . . 27 APPENDIX. FIRST. THE SUN'S CORONA AND His SPOTS. By RICHARD A. PKOCTOR, ........... 2g SECOND. THE FUEL OF THE SUN. By RICHARD A. PROCTOR, . 42 " THIRD. THE FUEL OF THK SUN. A REPLY by W. M. WILLIAMS, 45 14 DAY USE RETURN TO DESK FROM WHICH BORROWED LOAN DEPT. 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