276 HISTOKY OF ASTRONOMY. 



ceive a pinion at one end and a handle at the other. The 

 pinion fits a rack which encircles the rail; while the 

 handle and also the operator move round with the dome, 

 which is accomplished by the peculiar construction of the 

 observer's seat. This is a Small flight of stairs, having 

 an angle of elevation suited to the sweep of the eye-piece, 

 so that each step makes a convenient seat. The frame is 

 of wrought iron ; the string pieces are secured to the base 

 of the dome, and the bottom of the stairs rests upon two 

 wheels, in which grooves are made to fit a circular iron 

 rail which is secured to the floor. A circular table is 

 substituted for the ordinary reading steps. It is sup- 

 ported upon legs, with rollers, and is secured at each end 

 to the bottom steps of the observer's seat so as to revolve 

 with it- 

 Three stout beams rest upon the brick walls across the 

 center of the octagon, making a support for the pedestal 

 of the telescope. This pedestal is a drum of boiler iron, 

 three feet in diameter, and the same in -height. It is lined 

 with brick like a well, and covered with a smooth, round 

 flag-stone, projecting an inch over the iron. The mahog- 

 any frame of the telescope, having four feet with adjust- 

 ing screws, stands upon this stone. 



The telescope is an achromatic refractor of eight inches 

 aperture, and ten and a half feet focal length, made by 

 Henry Fitz. It has six negative eye^pieces, magnifying 

 from 60 to 480 times. The stand is made of cast iron, 

 excepting the circles, which are of brass ; and a clock is 

 attached to the telescope for keeping the object in the 



