of oxygen. The presence of these substances in the sun is hardly doubted, but their identification is difficult. A chief source of complication in research of this kind is the effect on the spectra of substances produced by differences of temperature and pressure. Excessive heat seems to dissociate the groups of atoms forming the molecules into simpler groups, and thus produces a different spectrum difficult to recognize. The labors of Lockyer, Huggins, Janssen, Draper, and others are directed toward overcoming these and other obstacles. 4. Physical Constitution of the Sun.-Since the first discovery by Galileo of those remarkable phenomena on the sun called sun spots-dark patches with an area frequently exceeding several times the surface of the earth-an immense variety of theories as to the probable constitution of the solar body has been brought forward by nearly every observer. Solar photography promises valuable aid in this research by enabling us to keep a permanent record of passing phenomena, ready at any time for deliberate measurement and comparison. One of the most important discoveries in connection with sun-spots, science owes to Dr. Alexander Wilson of Glasgow, who, in the year 1769, observed certain general and remark able features of sun-spots, which enabled him to establish the significance of these phenon. ena for a solution of the question as to the sun's physical constitution. These features are as follows: When a spot was near the middle of the sun, it was found to consist of a dark central part, called the nucleus or umbra, and around this was a comparatively brighter envelope, called the penumbra, and at such a time both parts were distinctly visible. But as the spot approached one border, the penumbra on the side nearest the observer became gradually more and more foreshortened, while the penumbra on the other side grew broader and broader, and at length, as the spot was disappearing-that is, passing the edge of the limb-the near side of the penumbra, as well as the dark central part, entirely vanished, nothing remaining except the opposite penumbra. When a spot made its appearance on the other side of the border, Wilson noticed the same phenomena in an opposite order, and soon discovered that they were nearly universal. It followed from these observations at once that every spot presents the appearance of a funnel-shaped opening in the sun's body, which, by the rotation of the latter, successively presented the described appearances. These observations have been abundantly confirmed by the photographic records of Messrs. De la Rue, Stewart, and Loewy. Schwabe showed, as the result of nearly 40 years' observations, that the number of groups of sun-spots is not the same from year to year, but has a maximum about every 10 or 11 years; and Gen. Sabine recorded the wonderful fact that the various epochs of maximum spot frequency are also those of maximum disturbance of our earth's magnetism. Here, then, we have a very curious bond of union between the sun and the planets of our system. It was next shown by Carrington that sun-spots have a proper motion of their ownthose near the solar equator moving faster than those near the poles. While spots are darker than the general surface of the sun, there are also frequently observed patches brighter than the general surface. These are called faculæ, and they generally accompany spots, most frequently in their wake; but they are only distinctly visible near the sun's limb, and lose their specific luminosity near the center of the sun's disk. Another phenomenon connected with our luminary is not less remarkable than sun-spots. This is the red flames, or protuberances, which were first observed surrounding the sun's disk on the occasion of a total eclipse, but which by ingenious methods of observation can now be rendered visible even when the sun is not eclipsed. This colored envelope, less brilliant than the photosphere, or light-giving surface, and having a mean height of 5,000 or 6,000 miles, is known as the chromosphere, and seems to consist mainly of incandescent hydrogen, jets of which are seen at times to be projected to a height of 200,000 miles." The velocity of these movements has been calculated to exceed at times 120 miles a second. Above the chromosphere there is a far deeper layer of cooler, sub-incandescent gases, among which is an unknown substance, which chiefly composes the outer portion, and is apparently lighter than hydrogen. These gaseous envelopes, extending together to 300,000 or even 500,000 miles above the photosphere, are now believed to cause the appearance called the corona, or white halo, which is seen to surround the dark body of the moon during an eclipse of the sun. If a spot be a hollow, as we have reason to suppose, it is only necessary to believe that there has been a descending current of this cold absorbing atmosphere to account for the want of luminosity. In like manner, on this hypothesis, a facula will be a portion of the luminous matter, which has been removed high up into the atmosphere, and which thus escapes the absorbing influence of the atmosphere. A spot may thus be supposed, to be produced by two currents-one ascending, and carrying the hot luminous matter up; the other descending, and carrying the cold atmosphere down. The photosphere is thus in a constant state of agitation like ebullition. Spots and their accompanying faculæ are an indication of the activity of those "convection currents" by which heat is brought to the surface to replace what has been radiated off. Their temporary prevalence then is held to be a sign of more than ordinary solar activity or expenditure of energy. This is palpably manifested on our globe in the greater magnetic disturbance that takes place when sun-spots are numerous, as Sunday. before mentioned. The diurnal range of the magnet freely suspended in the Kew observatory, shows an unmistakable correspondence with the waxing and waning of the spotted area on the sun; and the frequency of aurora is found to be in perfect correspondence with prevalence of spots. It is natural to seek to connect cycles of weather with the spot-period of the sun, but nothing has yet been conclusively established. A coincidence has seemingly been made out between the recurrence of famines in southern India through deficient rain and the period of minimum spots; but the coincidence does not hold for other localities. Attempts have even been made to bring commercial crises and other recurring events into the spot-cycle. As to the cause of the periodicity of sun-spots, observations made at Kew seem to establish a connection between the behavior of spots and the proximity of prominent planets; and it may thus be found that the recurrence of certain planetary positions in some way determines the spot-period. It was thought that the transit of 1874 would furnish data for obtaining the sun's parallax to within 0.10, but the result has been disappointing. The distance obtained from the American photographs-213 in number-is 92,028,000 m., using the figures given by Col. Clark for the dimensions of the earth. The transit method of determining the sun's distance has been found to be not as accurate as it had for a long time been supposed; still a large number of thoroughly equipped expeditions observed the transit of 1882, and the results were generally satisfactory. Prof. Ball places the sun's dis tance at 92,700,000 m., and estimates the error to be not more than 300,000 m. Dr. Hastings, in 1879-80, conducted a series of experiments, which resulted in finding a slight difference between the spectra of the center and the limb of the sun, the difference being about the same as that between the spectra of a spot and the unbroken photosphere. From his investigations he formulated a theory of convection currents, starting from a lower level, where all the substances would be vaporized; as it rises heat is lost, and condensation and precipitation take place. This precipitation forms the granules. When a downward convection current is increased, there is a rush of vapors to that point, carrying along the precipitated clouds (or smoke) which at this point congregate and form a spot. During the total eclipse of 1883, May, the corona was carefully studied, and Dr. Hastings concludes that it is due mainly to diffraction phenomena, and that the corona is only a narrow belt. Janssen also finds in it a large amount of reflected light. In one coronal stream Tacchini discovered green and yellow bands, which are characteristic of comets. Huggins has been trying to obtain photographs of the corona without an eclipse, and it has been thought that he has gotten a true picture, at least as far as 8' from the sun's limb. Photographs of the corona taken near the maximum period of spots have been found alike, and those at the minimum period also alike, seeming to establish a connection between the spot periods and the corona. Prof. Langley, in 1882, conducted a series of experiments upon the summit of Mt. Whitney, from which he concludes that the heat radiation of the sun is much greater than has been supposed. In 1882 Dr. Siemens explained, before the Royal Soc. of Lordon, a new theory of the origin of solar heat: he supposes space to be filled with something more substantial than ether; or that oxygen, hydrogen, nitrogen, and some of their compounds exist in space in a highly rarefied condition. The attraction of the sun causes a constant inflow of this cosmical matter, and its rotation projects it out in a stream at the sun's equator. During the inflow these substances pass from their rarefied condition to one of greater compression and higher temperature, until, near the sun's surface, they ignite, developing great heat; and after a while they are thrown off at the equator into space, where they again become dissociated. On this hypothesis it is this constant inflow and outflow that keeps up the undiminished heat of the sun. SUN AND FIRE WORSHIP. All investigation tends to show that nature-worship was the basis of all polytheistic religions, and that the chief deities of the several mythologies were originally personifications of the sun, or of particutar influences of the sun. The original solar nature of Jupiter, Zeus, Odin, Baal, Amen Ra (see EGYPT), Indra, etc., can hardly be mistaken. See those heads; also SCANDINAVIAN MYTHOLOGY, PHENICIA; and for a full devolpment of the subject, Max Müller's essay on Compara tive Mythology (Oxford Essays; 1856). The actual sun, however, still continued an object of worship, more especially as in the abstract and more strictly personal gods, moral and intellectual attributes came to predominate over and obscure the physical (see HELIOS); and with the worship of the sun was more or less closely associated that of fire his representative on earth. See PARSEES, NEEDFIRE, BELTEIN. The most complete system of sun-worship that we have any account of is that existing in Peru when discovered by the Spaniards (1526). "Our northern natures can hardly comprehend how the sun, and the moon, and the stars were imaged in the heart of a Peruvian, and dwelt there; how the changes in these luminaries were combined with all his feelings and his fortunes; how the dawn was hope to him; how the fierce mid-day brightness was power to him; how the declining sun was death to him; and how the new morning was a resurrection to him; nay, more, how the sun, and the moon, and the stars were his persoual friends, as well as his deities; how he held communion with them, and thought that they regarded every act and word; how, in his solitude, he fondly imagined that they sympathized with him, and how, with outstretched arms he appealed to them against their own unkindness, or against the injus |