14 



POPULAR SCIENCE MONTHLY 



Observatory provided the first requirement of this new work, namely, 

 a large solar image, having a diameter of seven inches as compared 

 with the two-inch image given by the Kenwood telescope. The con- 

 struction of a spectroheliograph large enough to photograph such an 

 image of the sun involved serious difficulties, but these were finally 

 overcome. The Eumford spectroheliograph, designed to meet the 

 special conditions of the new work, was constructed in the instrument 



Fig. 6.— The Sun showing the Calcium Flocculi {H„ Level). 1903, August 12, 8h 52 m . C.S.T. 



shop of the Yerkes Observatory, and is now in daily use with the forty- 

 inch telescope (Fig. 5). 



In this instrument the solar image is caused to move across the 

 first slit by means of an electric motor, which gives the entire telescope 

 a slow and uniform motion in declination. The sun's light, after 

 passing through the first slit, is rendered parallel by a large lens at the 

 lower end of the collimator tube. The parallel rays from this lens 

 fall upon a silvered glass mirror, from which they are reflected to the 

 first of two prisms, by which they are dispersed into a spectrum. 



