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POPULAR SCIENCE MONTHLY. 



motors provided for the purpose. When once directed toward the object 

 to be observed it will frequently happen that the lower end of the tele- 

 scope is far out of reach above the observer's head. For this reason the 



Fig. 5. 

 The korty-ixch telescope of the Yerkes Obseevatory. 



entire floor of the observing room, 75 feet in diameter, is constructed 

 like an electric elevator, which by throwing a switch can be made to 

 rise or fall through a distance of twenty-three feet. Thus the lower 

 end of the telescope is rendered accessible even for objects near the 



