AIDS OF THE NEWTONIAN PERIOD. 471 



serving, by finding that Hevelius refused to adopt them because they 

 would make all the old observations of no value. He had spent a 

 laborious and active life in the exercise of the old methods, and could 

 not bear to think that all the treasures which he had accumulated had 

 lost their worth by the discovery of a new mine of richer ore. 



[2d Ed.] [Littrow, in his Die Wunder des Himmcls, Ed. 2, pp. 

 684, 685, says that Gascoigne invented and used the telescope with 

 wires in the common focus of the lenses in 1640. He refers to Phil. 

 Trans, xxx. 603. Picard reinvented this arrangement in 1667. T 



O 



have already spoken of Gascoigne as the inventor of the micrometer. 



Romer (already mentioned, p. 464) brought into use the Transit 

 Instrument, and the employment of complete Circles, instead of the 

 Quadrants used till then ; and by these means gave to practical astron- 

 omy a new form, of which the full value was not discovered till long 

 afterwards. 



The apparent place of the object in the instrument being so precisely 

 determined by the new methods, the exact Division of the arc into 

 degrees and their subdivisions became a matter of great consequence. 

 A series of artists, principally English, 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 Green- 

 wich ; for Bradley he constructed the Sector which detected aberra- 

 tion. He also made the Sector which the French academicians 

 carried to Lapland ; and probably the goodness of this instrument, 

 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 observatories. His method of dividing was con- 

 sidered so perfect, that the knowledge of it was purchased by the Eng- 

 lish government, and published in 1767. Ramsden was equally cele- 

 brated. 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 construct >d Mural Circles only, holding this to be a kind 01 

 instrument far superior to the quadrant. He made one of five feet 

 diameter, in 1788, for M. Piazzi at Palermo; and one of eight feet foi 

 the observatory of Dublin. Troughton, a worthy successor of the art 



1 Jlont. iv. 837. 



