222 HISTOKY OF ASTRONOMY. 



the roof, thus affording an uninterrupted view of the 

 celestial meridian from the southern to the northern 

 horizon. 



- 



f In the year 1840, Professor Bartlett visited the prin- 

 / cipal observatories in England, Scotland, Ireland, France, 

 Belgium, and Bavaria, and ordered three large instru- 

 ments, viz., an equatorial telescope, a transit instrument, 

 Vv and a mural circle. 



The equatorial, which was erected in the central tower, 

 was mounted by Mr. Thomas Grubb, of Dublin. The 

 telescope, made by Lerebours, of Paris, is a refractor of 

 eight feet focal length, and six inches aperture. It has a 

 position micrometer, furnished with an illuminating ap- 

 paratus for bright lines and dark field. The telescope is 

 moved by clock-work, so that the object under ex- 

 amination is easily kept in the center of the field of 

 view. 



In the east tower is a transit telescope, by Ertel. and 

 Son, of Munich. It has a clear aperture of five and a 

 quarter inches, with a focal length of seven feet, and is 

 supplied with all the appendages necessary to facilitate 

 the making of observations. There is in this tower a fine 

 sidereal clock, by Hardy. 



In the west tower is a mural circle, by Simms, of Lon- 

 don. It is cast in one entire piece of brass, instead of 

 the old mode of frame-work. Its diameter is five feet, 

 and the graduations are upon two bands, one of gold the 

 other of palladium. The telescope has a clear aperture 

 of four inches, and a focal length of five feet. It is pro- 



