SPECTROHELIOGRAPH

An instrument for photographing the sun’s surface in light of any desired wave length. It is used for determining the position of the various elements of which the sun is composed, and the character of the solar prominences. The instrument was devised in 1889 by Profe or Hale of the University of Chicago, and consists of a spectroscope with a double slit in accordance with the suggestion made by Jan en in 1869. A sensitive _ photographic plate is placed behind the secondary slit, which serves to exclude all light except that of the desired wave length which is determined by the various adjustments of the instrument. The two largest spectroheliographs are located at the Yerkes and the Mount Wilson observatories. S (5/6) s (5/6)