The last of the five eclipses which we have grouped together for separate consideration was visible in Southern India and Australia, December 12, 1871. Some splendid photographs were secured by the English parties on the Malabar coast, showing, for the first time, the remarkable branching forms of the coronal emanations; but the most conspicuous result was Janssen's detection of some of the dark Fraunhofer lines, long vainly sought in the continuous spectrum of the corona. Chief among these was the D-line of sodium, the original index, it might be said, to solar chemistry. No proof could be afforded more decisive that this faint _echoing back_ of the distinctive notes of the Fraunhofer spectrum, that the polariscope had spoken the truth in asserting a large part of the coronal radiance to be reflected sunlight. But it is usually so drenched in original luminosity, that its special features are almost obliterated. Janssen's success in seizing them was due in part to the extreme purity of the air at Sholoor, in the Neilgherries, where he was stationed; in part to the use of an instrument adapted by its large aperture and short focus to give an image of the utmost brilliancy. His observation, repeated during the Caroline Island eclipse of 1883, was photographically verified ten years later by M. de la Baume Pluvinel in Senegal.[532] An instrument of great value for particular purposes was introduced into eclipse-work in 1871. The "slitless spectroscope" consists simply of a prism placed outside the object-glass of a telescope or the lens of a camera, whereby the radiance encompassing the eclipsed sun is separated into as many differently tinted rings as it contains different kinds of light. These tinted rings were simultaneously viewed by Respighi at Poodacottah, and by Lockyer at Baikul. Their photographic registration by the latter in 1875 initiated the transformation of the slitless spectroscope into the prismatic camera.[533] Meanwhile, the use of an ordinary spectroscope by Herschel and Tennant at Dodabetta showed the green ray of coronium to be just as bright in a rift as in the adjacent streamer. The visible structure of the corona was thus seen to be independent of the distribution of the gases which enter into its composition. By means, then, of the five great eclipses of 1860-71 it was ascertained: first, that the prominences, and at least the lower part of the corona, are genuine solar appurtenances; secondly, that the prominences are composed of hydrogen and other gases in a state of incandescence, and rise, as irregular outliers, from a continuous envelope of the same materials, some thousands of miles in thickness; thirdly, that the corona is of a highly complex constitution, being made up in part of glowing vapours, in part of matter capable of reflecting sunlight. We may now proceed to consider the results of subsequent eclipses.