THE SNOW TELESCOPE. 



A step in this direction was the horizontal tele- 

 scope, which the late Miss Snow had presented to 

 the Yerkes Observatory through the kind interest 

 and assistance of Dr. George S. Isham. It con- 

 sists of a coelostat, with a plane mirror 30 inches 

 in diameter, rotated by clockwork at such a rate 



FIG. 8. Coelostat and second mirror of Snow Telescope. 



as to keep the beam of sunlight, reflected from its 



silvered (front) surface, in a fixed position on a 

 second plane mirror standing above and south 

 of it. From this mirror the beam is reflected 

 nearly horizontally to a point 100 feet north, where 

 it falls on a 24-inch concave mirror of 60 feet focal 

 length, which forms a solar image about 6 l /i inches 



