74 



this comparison, the annual motions in north polar distance, 

 as given in the last catalogue of Dr. Maskelyne, have been 

 used. These certainly are in several instances inaccurate 

 from the proper motions used, and to this may be attributed 

 some of the differences between 1809 and 1813, but it is by 

 no means a sufficient explanation as to others. In the case 

 of /S Leonis, particularly, there appears a difference that I 

 cannot attempt to account for. Considerable differences be 

 tween the results of observations of the same star when se- 

 parated by several years have, however, been before ob- 

 served in several instances, and yet remain to be accounted 

 for. A comparison of the means of the results of the ob- 

 servations of Dr. Hamilton, at Armagh, M. Piazzi, at Pa- 

 lermo, and Mr. Pond, at Westbury made about the. sfime 

 period, (Phil. Trans. 1806) and of the present results of the 

 Greenwich, and of our instrument, furnishes a striking in- 

 stance. A comparison some years hence of the present results 



and of new ones obtained by the, same instruments will pyo- 



. uiJ ca ii 4*, V^ a= *^t 4- 



bably clear up this pomt. ., ,^ 



■It mav also be remarked that the observations in 1809 



were computed by Bradley's refractions, and also no, '^tt^^- 



tion was paid to the circumstance of parallax. The resujts 



of 1813 are from, observatibns made when the zenith dia- 



tjance^ from the, effects of parallax were greatest and! least. 



...jflence also perhaps may be explained part of the differences 



k) cQlunrin JP. 



