ASTRONOMICAL OBSERVATORIES. 267 



cular room in the rotunda, 17 feet in diameter, is in- 

 tended for a library, and communicates directly with the 

 observer's rooms in the north and south wings. The 

 square brick equatorial pier, four feet in diameter, rises 

 through the middle of the room without touching the 

 flooring or ceiling, and is capped with a cylindrical 

 granite block nearly 6 feet in diameter, and 15 inches 

 thick. The pier contains a Tecess, having double glazed 

 doors, and a space of dead air on all sides, for the recep- 

 tion of a clock, to be connected with an electro-chrono- 

 graph. The pier is also surrounded by the book-shelves, 

 which are entirely detached from it. 



The observer's rooms are in the north and south wings, 

 and are each 21 by 14 feet, and have each a slit in the 

 roof two feet wide, the north one having a corresponding 

 pier for prime vertical observations. 



The transit room, 18 by 14 feet, in the east wing, has 

 two slits, the eastern one having a corresponding pair 

 of piers for the meridian circle, and the other a single 

 pier for the use of portable instruments. The entrance 

 hall, 14 by 11 feet, in the center of the building, opens 

 directly into all the rooms except the library. 



The foundation for the dome of the equatorial room 

 consists of circular segments of planks, firmly secured 

 together, and bolted to the walls below. Upon this, 

 and directly over the middle of the inner wall, are 

 screwed twelve segments of a circular cast-iron rail, 

 three inches wide, with a circular channel three eighths 

 of an inch deep. Between this and a corresponding 



