The Solar Prominences

Abstract

IT may interest some of your readers to hear that the bright lines of the hydrogen “flames” extending beyond the sun's disc can be seen with much less instrumental aid than has hitherto been considered indispensable. I have succeeded in seeing them quite unmistakably by the following very simple means. I fixed one of Mr. Browning's direct vision spectroscopes (having seven prisms) on a board which also carried a two-inch object-glass belonging to a good field telescope. I mounted the instrument thus arranged (shall I say as an altazimuth) on the back of an ordinary bed-room mirror, and directed it at the sun. The slit was set so as nicely to divide the D line, and a blue glass was generally interposed in front of the slit to sift the light. As the image of the sun traversed the slit at intervals, the flames appeared as bright prolongations of the F line extending beyond the sun's limb. It was also clearly seen at times that these prolongations were narrower than the F line and were not in the centre of it, also that they were frequently detached from the sun's limb, and sometimes they were not straight: appearances depending as is generally supposed on the velocity and pressure of the gas in the flame. The flames were also readily seen in the C line. In observing the solar spectrum I have found coloured glasses in front of the slit very useful to shut out as much as possible of the light from the parts of the spectrum not under observation. By using the spectroscope without its slit and collimating lens, and directing it towards the great nebula in Orion, it shows close together three bright images of the nebula exhibited on a continuous spectrum.