396 HISTOKY OF ASTRONOMY. 



whose attachment is such as allows the tube to be 

 turned while the clock is in operation. 



In the west wing is placed the meridian circle, which 

 was made by "W. J. Young, of Philadelphia. It has an 

 excellent telescope of 4 inches aperture, and 5 feet focus, 

 with two circles 26 inches in diameter, one of which 

 reads by four verniers to two seconds of arc ; the other 

 is used simply as a finder. The instrument is supported 

 by marble piers, five feet high, firmly based on masonry. 



In the eastern wing is a sidereal clock by Harpur, 

 of Philadelphia ; and in the same room is the magnetic 

 register. Upon an inward projection of the eastern 

 wall of the center building, is mounted a prime vertical 

 transit instrument 20 inches in length, made by Dollond. 

 This is included in the dome containing the equatorial. 

 The cost of the building was $2,500, and that of the 

 instruments contained in it about $4,500. This ob- 

 servatory is in charge of Professor Joseph G. Harlan. 



