SCIENCE AT THE UNIVERSITY OF CHICAGO. 803 



scope ever constructed, having a forty-inch objective made by 

 Alvan Clark & Sons. The focal length of the instrument is 

 sixty- four feet. The mounting is similar to that of the great Lick 

 telescope, but is heavier, more rigid, and improved. One impor- 

 tant advantage introduced for the first time in this mounting is 

 the system of electric motors, by means of which the various 

 motions are effected. By simply touching buttons upon a little 

 keyboard the astronomer may produce any one of ten different 

 results, changing the position of the instrument or of parts of the 

 observatory itself. In this simple way the great instrument may 



FIG. 10. YERKES OBSERVATORY, LAKE GENEVA. 



be moved, the clock may be started or stopped, the shutter of the 

 dome may be opened or closed, the dome itelf may be revolved, 

 or the floor may be made to rise and fall. The dome covering the 

 telescope is about ninety feet in diameter, with an observing slit 

 twelve feet wide extending from the horizon to beyond the zenith. 

 Two spectroscopic attachments are connected with the great 

 telescope: (a) a spectroheliograph for photographing the solar 

 chromosphere, prominences, and faculse by monochromatic light 

 combined with a large solar spectroscope for photographic and 

 visual study of solar phenomena ; (b) a stellar spectroscope 

 for photographic and visual investigation of stellar spectra, and 

 determination of motion in the line of sight. The world has a 

 right to expect results from such an instrumental equipment, and 

 the Department of Astronomy has in view important researches. 

 Among these are micrometrical measurement of double stars and 



