248 HISTORY OF ASTRONOMY. 



turned through a whole revolution by a single individual, 

 without any very great exertion, in thirty -five, seconds. 



The central pier for the support of the telescope is 

 of granite, and is in the form of ^ frustum of a cone 

 22 feet in diameter at the base, and 10 feet at the top. 

 It is 40 feet high, and rests on a wide foundation of 

 .grouting composed of hydraulic cement and coarse 

 gravel, 26 feet below the natural surface of the ground, 

 and is entirely detached from every other part of the 

 building. Upon the top of the pier is laid a circular 

 cap-stone, 10 feet in diameter, and 2 feet thick, on which 

 stands, by three bearings, the granite block, 10 feet in 

 height, to which the metallic bed-plate of the telescope 

 is firmly attached by bolts and screws. Five hundred 

 tons of granite were used in the construction of this 

 pier. 



Upon the east side of this tower is a small wing for 

 the accommodation of the transit circle and clock ; and 

 on the north side is a similar wing, designed for a transit 

 in the prime vertical. The house for the accommodation 

 of the observer is connected with the east wing. The 

 western wing is used for magnetic and meteorological 

 observations. This wing was erected in the years 

 1850-51, making the entire length of the building 160 

 feet, and adds greatly to the architectural beauty of the 

 observatory. In the small dome is placed the smaller 

 equatorial, of 5 feet focal length, and 4 and 1-8 inch 

 aperture, made by Merz, which is a remarkably fine 

 instrument. 



