The advance of photography : its history and modern applications (1911)

290 THE ADVANCE OF PHOTOGRAPHY the nature of the protuberances was solved. Jansen determined at the same time the exact position of these bright lines, and discovered that the gaseous substance was glowing hot hydrogen. He subsequently made the discovery that an eclipse was by no means necessary in order to detect the bright lines of the protuberances. They are seen on clear days if the slit of a spectroscope be directed on the sun's rim, and the changeable nature of these protuberances can every day be observed by the appearance and disappearance of these bright lines. Zollner of Leipzig even detected with the spectroscope a sudden burst of gas, also the sudden breaking away of gas clouds from their substratum, and their dispersion, all in the space of a few minutes. We add a copy of the Aden photographs, taken from Herr Schellen's work on spectral analysis. The first view (Fig. 118) gives us the eastern rim of the sun ; the western was covered by clouds. It is easy to recognize in it the large, horn-like protuberance, which has an elevation of 184,000 miles, and gives an idea with what immense force masses of gas are projected from the surface of the sun. It shows, further, the remarkable protuberance to the left, in which the masses of gas appear like powerful jets of flame driven sideways by a tempestuous wind ; a light region surrounding the protuberances forms the glowing hot stratum of vapour permanently surrounding the rim, named chromosphere. The second view (Fig. 119) gives a representation of the total eclipse as it was observed in India. Besides the protuberances seen at Aden, there is another on the western rim of the sun, which was quite covered by clouds at Aden. Photography was soon applied to the observation of total eclipses on a more magnificent scale. Thus, on the 7th of August 1869, hundreds of photographers were actively employed in observing the total eclipse of