ASTRONOMICAL CIRCLE. OQ j 



The advantages that have resulted from the excellent Method of ob- 

 jnethod persued at Greenwich, of observing constantly the serving, &c. 

 transits of a few stars, to obtain accurately their right ascen- 

 sions, induced me to follow the same method for determining 

 their declinations ; and for a considerable period I constantly 

 observed them on the meridian, whenever they passed at a 

 convenient hour; usually reversing the instrument in azimuth 

 at the end of every day's observation ; never considering any 

 observation as complete that had not its corresponding one in 

 a short interval of time. When this circumstance is not at- 

 tended to, 1 think, a great part of the advantage arising from 

 the circular construction is lost. 



The observations themselves will show, if they have been Accuracy of 

 made with the requisite care and attention to merit the notice ^^^ observa- 

 of astronomers ; for it is one of the many advantages ofcircular 

 instruments, that, from the observations made witli them, we 

 tnay infer with great precision not only tjie mean probable 

 error, but likewise the greatest possible error to which they 

 are liable. Frorp a careful comparison ot the errors of collima- Greatest error 

 tion, as deduced from different stars, I concluded that the "f coUimaiion. 

 greatest possible error was 2",5, and the mean error about l"; 

 and by a comparison with other observations with similar in- 

 struments, it will be seen that this supposition was well founded, 

 since nearly the same quantities are deduced by another method 

 to be considered hereafter. 



The polar distances are annexed to each observation: apoioj- 

 method which I borrowed from Mr. Wollaston, and which 

 is rendered veryeasy by employing his useful tables calculated 

 for that purpose. This practice of reducmg every day's obser- 

 vations cannot be too mucu recommended, as the labour of 

 calculating accumulated observations is thus rendered un- 

 necessary. 



When I had deduced the declinations of these stars from Comparison 



my own observations, continued long enough to divest them ^^^'^^ °^"" °^' 



•' ^ ° , ° servations. 



of ali error, except that arrising from defect in the divisions of 



the instrument. I was desirous ot comparing them with the 

 observations made by the o'.hers; and 1 have subjoined a com- 

 parison of them with all those wiiich 1 could procure, that 

 seemed entiticd to confidence. In the first column are the 

 observations made at Greenwich, as published in 1802 by — namely, at 

 the Astronomer Royal J the second column, contains a Cata- ^"^^^'"Y^^^' ^' 



' Armagh, at 



logue Palermo, and 



