43 



cumstance of tlie telescope admitting of being shifted to dif- 

 ferent parts of the circle i the number of microscopes used, 

 and the firmness of their position in the pier; and the great 

 knowledge, skill and assiduity of Mr. Pond, the Astronomer 

 Roj-al, all promise very important results for Astronomy. 



There is, however, one circumstance to be noticed, respect- 

 ing this method of observing, of some importance, and which 

 bears particularly on tlie question, whether any of the fixed 

 stars have a visible parallax. 



In the mode of ascertaining the north polar distance of an 

 object by the mural circle, it is requisite to know the north 

 polar distances of certain fixed stars with the changes from 

 precession, effects of the semi annual equation, aberration, nur 

 tation and refraction. If some of these stars be also affected 

 by annual parallax, it is obvious that if no notice be taken of 

 this, the north polar distance required will be inexact. It 

 may be said that the same correction being obtained by dif- 

 ferent stars, will shew that no such annual parallax exists so 

 as to be sensible. This point certainly might be ascertained 

 in this manner b}' a sufficiently numerous set of observations. 

 Still, as it may be suggested, that many of the fixed stars 

 may have small sensible annual parallaxes, observations, 

 which will point out only the difl'crences of these, are not 

 so proper as those by which the whole quantity would be 

 pointed out. This may perhaps be better understoood by 

 considering what would have taken place had this mode ol 



observing been used before the discovery of the aberration 



II 2 



