274 HISTORY OF PHYSICAL ASTRONOMY. 



and their subdivisions became a matter of great 

 consequence. A series of artists, principally Eng- 

 lish, have acquired distinguished places in the lists 

 of scientific fame by their performances in this 

 way ; and from that period, particular instruments 

 have possessed historical interest and individual 

 reputation. Graham was one of the first of these 

 artists. He executed a great Mural Arc for Halley 

 at Greenwich; for Bradley he constructed the Sector 

 which detected aberration. He also made- the 

 Sector which the French academicians carried to 

 Lapland ; and probably the goodness of this instru- 

 ment, compared with the imperfection of those 

 which were sent to Peru, was one main cause of 

 the great difference of duration in the two series 

 of observations. Bird, somewhat later 1 , (about 

 1750,) divided several Quadrants for public obser- 

 vatories. His method of dividing was considered 

 so perfect, that the knowledge of it was purchased 

 by the English government, and published in 1767. 

 Ramsden was equally celebrated. The error of 

 one of his best Quadrants (that at Padua) is said 

 to be never greater than two seconds. But at a 

 later period, Ramsden constructed Mural Circles 

 only, holding this to be an instrument far superior 

 to the quadrant. He made one of five feet dia- 

 meter, in 1788, for M. Piazzi at Palermo; and one of 

 eight feet for the observatory of Dublin. Trough- 

 ton, a worthy successor of the artists we have 

 1 Mont. iv. 337- 



