The corona appears under different forms, and has never been observed twice alike. Its dimensions are also subject to considerable variations. Sometimes it appears regular and very little extended, its distribution around the Sun being almost uniform; although in general it spreads a little more in the direction of the ecliptic, or of the solar equator. At other times it appears much larger and more complicated, and forms various wings and appendages, which in some cases, as in 1878, extend to immense distances; while delicate rays radiate in straight or curved lines from the spaces left in the polar regions between the wings. The corona has sometimes appeared as if divided by immense dark gaps, apparently free from luminous matter, and strongly resembling the dark rifts seen in the tails of comets. This was observed in Spain and Sicily during the total eclipse of the Sun in 1870. Different structures, forming wisps and streamers of great length, and interlaced in various ways, are sometimes present in the corona, while faint but more complicated forms, distantly resembling enormous solar protuberances with bright nuclei, have also been observed. As the Moon continues its eastward progress, it gradually covers the chromosphere and the solar protuberances on the eastern side of the Sun; while, at the same time, the protuberances and the chromosphere on the opposite limb gradually appear from under the retreating Moon. Then, the thin arc of the reversing layer is visible for an instant, and is instantly followed by the appearance of a point of dazzling white light, succeeded immediately by the apparition of Daily's beads on each side, and totality is over, with this third contact. The corona continues to be visible on the eastern side of the Sun for several minutes longer, and then rapidly vanishes. The thin solar crescent increases in breadth as the Moon advances; while, at the same time, the darkness and gloom spread over nature gradually disappear, and terrestrial objects begin to resume their natural appearance. Finally the limb of the Moon separates from that of the Sun at the instant of "fourth contact," and the eclipse is over.