Page:Popular Science Monthly Volume 60.djvu/254

246 above the photosphere is as great as 4,000 miles. The bright lines are identified as belonging to iron, titanium, chromium, hydrogen and other elements. The origin of some of the lines is unknown.

Although no other time may be so favorable for the study of the reversing layer as at total eclipses, the chromosphere and prominences may nevertheless be well studied on any clear day.

In connection with the eclipse of 1868 Janssen and Lockyer each independently discovered that by spectroscopic means the light of the chromosphere and prominences may be so separated from that of the sky as to become visible without an eclipse. The light from the region just outside the sun's limb is composed of skylight and the light of the solar atmosphere. Each is about equally bright. When this combined light is passed through a prism, that due to the sky is spread out into a continuous surface, thus becoming much fainter, while that due to the chromosphere or prominence, from its gaseous nature, is collected into bright bands, which thus surpass the skylight in intensity and may be seen or photographed. This line of work has been

greatly extended by different scientists, notably by Hale, of this country, who, by a device known as the spectroheliograph, has succeeded in making, without an eclipse, photographs showing all the prominences surrounding the sun and the details of the solar surface at the same time. These photographs are made in monochromatic light. They represent what would be seen if the eye were sensitive to light of the wave-length of the K line only. Figures 3 and 4 show a great eruptive prominence photographed by Professor Hale, March 25, 1895. The interval between the two photographs was 24 minutes, during which time the prominence was thrown upward from a height of